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Four-stroke cycle used in gasoline/petrol engines: intake (1), compression (2), power (3), and exhaust (4). The right blue side is the intake port and the left brown side is the exhaust port. The cylinder wall is a thin sleeve surrounding the piston head which creates a space for the combustion of fuel and the genesis of mechanical energy.

A four-stroke (also four-cycle) engine is an internal combustion (IC) engine in which the piston completes four separate strokes while turning the crankshaft. A stroke refers to the full travel of the piston along the cylinder, in either direction. The four separate strokes are termed:

  1. Intake: Also known as induction or suction. This stroke of the piston begins at top dead center (T.D.C.) and ends at bottom dead center (B.D.C.). In this stroke the intake valve must be in the open position while the piston pulls an air-fuel mixture into the cylinder by producing a partial vacuum (negative pressure) in the cylinder through its downward motion.
  2. Compression: This stroke begins at B.D.C, or just at the end of the suction stroke, and ends at T.D.C. In this stroke the piston compresses the air-fuel mixture in preparation for ignition during the power stroke (below). Both the intake and exhaust valves are closed during this stage.
  3. Combustion: Also known as power or ignition. This is the start of the second revolution of the four stroke cycle. At this point the crankshaft has completed a full 360 degree revolution. While the piston is at T.D.C. (the end of the compression stroke) the compressed air-fuel mixture is ignited by a spark plug (in a gasoline engine) or by heat generated by high compression (diesel engines), forcefully returning the piston to B.D.C. This stroke produces mechanical work from the engine to turn the crankshaft.
  4. Exhaust: Also known as outlet. During the exhaust stroke, the piston, once again, returns from B.D.C. to T.D.C. while the exhaust valve is open. This action expels the spent air-fuel mixture through the exhaust port.

Four-stroke engines are the most common internal combustion engine design for motorized land transport,[1] being used in automobiles, trucks, diesel trains, light aircraft and motorcycles. The major alternative design is the two-stroke cycle.[1]

History

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Otto cycle

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Main article: Otto cycle
See also: Otto engine
An Otto Engine from 1880s US Manufacture

Nikolaus August Otto was a traveling salesman for a grocery concern. In his travels, he encountered the internal combustion engine built in Paris by Belgian expatriate Jean Joseph Etienne Lenoir. In 1860, Lenoir successfully created a double-acting engine that ran on illuminating gas at 4% efficiency. The 18 litre Lenoir Engine produced only 2 horsepower. The Lenoir engine ran on illuminating gas made from coal, which had been developed in Paris by Philip Lebon.[2]

In testing a replica of the Lenoir engine in 1861, Otto became aware of the effects of compression on the fuel charge. In 1862, Otto attempted to produce an engine to improve on the poor efficiency and reliability of the Lenoir engine. He tried to create an engine that would compress the fuel mixture prior to ignition, but failed as that engine would run no more than a few minutes prior to its destruction. Many other engineers were trying to solve the problem, with no success.[2]

In 1864, Otto and Eugen Langen founded the first internal combustion engine production company, NA Otto and Cie (NA Otto and Company). Otto and Cie succeeded in creating a successful atmospheric engine that same year.[2] The factory ran out of space and was moved to the town of Deutz, Germany in 1869, where the company was renamed to Deutz Gasmotorenfabrik AG (The Deutz Gas Engine Manufacturing Company).[2] In 1872, Gottlieb Daimler was technical director and Wilhelm Maybach was the head of engine design. Daimler was a gunsmith who had worked on the Lenoir engine. By 1876, Otto and Langen succeeded in creating the first internal combustion engine that compressed the fuel mixture prior to combustion for far higher efficiency than any engine created to this time.

Daimler and Maybach left their employ at Otto and Cie and developed the first high-speed Otto engine in 1883. In 1885, they produced the first automobile to be equipped with an Otto engine. The Daimler Reitwagen used a hot-tube ignition system and the fuel known as Ligroin to become the world's first vehicle powered by an internal combustion engine. It used a four-stroke engine based on Otto's design. The following year, Karl Benz produced a four-stroke engined automobile that is regarded as the first car.[3]

In 1884, Otto's company, then known as Gasmotorenfabrik Deutz (GFD), developed electric ignition and the carburetor. In 1890, Daimler and Maybach formed a company known as Daimler Motoren Gesellschaft. Today, that company is Daimler-Benz.

Atkinson cycle

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This 2004 Toyota Prius hybrid has an Atkinson-cycle engine as the petrol-electric hybrid engine
The Atkinson Gas Cycle
Main article: Atkinson cycle

The Atkinson-cycle engine is a type of single stroke internal combustion engine invented by James Atkinson in 1882. The Atkinson cycle is designed to provide efficiency at the expense of power density, and is used in some modern hybrid electric applications.

The original Atkinson-cycle piston engine allowed the intake, compression, power, and exhaust strokes of the four-stroke cycle to occur in a single turn of the crankshaft and was designed to avoid infringing certain patents covering Otto-cycle engines.[4]

Due to the unique crankshaft design of the Atkinson, its expansion ratio can differ from its compression ratio and, with a power stroke longer than its compression stroke, the engine can achieve greater thermal efficiency than a traditional piston engine. While Atkinson's original design is no more than a historical curiosity, many modern engines use unconventional valve timing to produce the effect of a shorter compression stroke/longer power stroke, thus realizing the fuel economy improvements the Atkinson cycle can provide.[5]

Diesel cycle

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Main article: Diesel cycle
Audi Diesel R15 at Le Mans

The diesel engine is a technical refinement of the 1876 Otto-cycle engine. Where Otto had realized in 1861 that the efficiency of the engine could be increased by first compressing the fuel mixture prior to its ignition, Rudolf Diesel wanted to develop a more efficient type of engine that could run on much heavier fuel. The Lenoir, Otto Atmospheric, and Otto Compression engines (both 1861 and 1876) were designed to run on Illuminating Gas (coal gas). With the same motivation as Otto, Diesel wanted to create an engine that would give small industrial companies their own power source to enable them to compete against larger companies, and like Otto, to get away from the requirement to be tied to a municipal fuel supply.[citation needed] Like Otto, it took more than a decade to produce the high-compression engine that could self-ignite fuel sprayed into the cylinder. Diesel used an air spray combined with fuel in his first engine.

During initial development, one of the engines burst, nearly killing Diesel. He persisted, and finally created a successful engine in 1893. The high-compression engine, which ignites its fuel by the heat of compression, is now called the diesel engine, whether a four-stroke or two-stroke design.

The four-stroke diesel engine has been used in the majority of heavy-duty applications for many decades. It uses a heavy fuel containing more energy and requiring less refinement to produce. The most efficient Otto-cycle engines run near 30% thermal efficiency.[clarification needed]

Thermodynamic analysis

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The idealized four-stroke Otto cycle p-V diagram: the  intake (A)  stroke is performed by an isobaric expansion, followed by the  compression (B)  stroke, performed as an adiabatic compression. Through the combustion of fuel an isochoric process is produced, followed by an adiabatic expansion, characterizing the  power (C)  stroke. The cycle is closed by an isochoric process and an isobaric compression, characterizing the  exhaust (D)  stroke.

The thermodynamic analysis of the actual four-stroke and two-stroke cycles is not a simple task. However, the analysis can be simplified significantly if air standard assumptions[6] are utilized. The resulting cycle, which closely resembles the actual operating conditions, is the Otto cycle.

During normal operation of the engine, as the air/fuel mixture is being compressed, an electric spark is created to ignite the mixture. At low rpm this occurs close to TDC (Top Dead Centre). As engine rpm rises, the speed of the flame front does not change so the spark point is advanced earlier in the cycle to allow a greater proportion of the cycle for the charge to combust before the power stroke commences. This advantage is reflected in the various Otto engine designs; the atmospheric (non-compression) engine operates at 12% efficiency whereas the compressed-charge engine has an operating efficiency around 30%.

Fuel considerations

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A problem with compressed charge engines is that the temperature rise of the compressed charge can cause pre-ignition. If this occurs at the wrong time and is too energetic, it can damage the engine. Different fractions of petroleum have widely varying flash points (the temperatures at which the fuel may self-ignite). This must be taken into account in engine and fuel design.

The tendency for the compressed fuel mixture to ignite early is limited by the chemical composition of the fuel. There are several grades of fuel to accommodate differing performance levels of engines. The fuel is altered to change its self-ignition temperature. There are several ways to do this. As engines are designed with higher compression ratios the result is that pre-ignition is much more likely to occur since the fuel mixture is compressed to a higher temperature prior to deliberate ignition. The higher temperature more effectively evaporates fuels such as gasoline, which increases the efficiency of the compression engine. Higher compression ratios also mean that the distance that the piston can push to produce power is greater (which is called the expansion ratio).

The octane rating of a given fuel is a measure of the fuel's resistance to self-ignition. A fuel with a higher numerical octane rating allows for a higher compression ratio, which extracts more energy from the fuel and more effectively converts that energy into useful work while at the same time preventing engine damage from pre-ignition. High octane fuel is also more expensive.

Many modern four-stroke engines employ gasoline direct injection or GDI. In a gasoline direct-injected engine, the injector nozzle protrudes into the combustion chamber. The direct fuel injector injects gasoline under a very high pressure into the cylinder during the compression stroke, when the piston is closer to the top.[7]

Diesel engines by their nature do not have concerns with pre-ignition. They have a concern with whether or not combustion can be started. The description of how likely diesel fuel is to ignite is called the Cetane rating. Because diesel fuels are of low volatility, they can be very hard to start when cold. Various techniques are used to start a cold diesel engine, the most common being the use of a glow plug.

Design and engineering principles

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Power output limitations

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The four-stroke cycle
1=TDC
2=BDC
 A: Intake 
 B: Compression 
 C: Power 
 D: Exhaust 

The maximum amount of power generated by an engine is determined by the maximum amount of air ingested. The amount of power generated by a piston engine is related to its size (cylinder volume), whether it is a two-stroke engine or four-stroke design, volumetric efficiency, losses, air-to-fuel ratio, the calorific value of the fuel, oxygen content of the air and speed (RPM). The speed is ultimately limited by material strength and lubrication. Valves, pistons and connecting rods suffer severe acceleration forces. At high engine speed, physical breakage and piston ring flutter can occur, resulting in power loss or even engine destruction. Piston ring flutter occurs when the rings oscillate vertically within the piston grooves they reside in. Ring flutter compromises the seal between the ring and the cylinder wall, which causes a loss of cylinder pressure and power. If an engine spins too quickly, valve springs cannot act quickly enough to close the valves. This is commonly referred to as 'valve float', and it can result in piston to valve contact, severely damaging the engine. At high speeds the lubrication of piston cylinder wall interface tends to break down. This limits the piston speed for industrial engines to about 10 m/s.

Intake/exhaust port flow

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The output power of an engine is dependent on the ability of intake (air–fuel mixture) and exhaust matter to move quickly through valve ports, typically located in the cylinder head. To increase an engine's output power, irregularities in the intake and exhaust paths, such as casting flaws, can be removed, and, with the aid of an air flow bench, the radii of valve port turns and valve seat configuration can be modified to reduce resistance. This process is called porting, and it can be done by hand or with a CNC machine.

Waste heat recovery of an internal combustion engine

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An internal combustion engine is on average capable of converting only 40-45% of supplied energy into mechanical work. A large part of the waste energy is in the form of heat that is released to the environment through coolant, fins, etc. If somehow waste heat could be captured and turned to mechanical energy, the engine's performance and/or fuel efficiency could be improved by improving the overall efficiency of the cycle. It has been found that even if 6% of the entirely wasted heat is recovered it can increase the engine efficiency greatly.[8]

Many methods have been devised in order to extract waste heat out of an engine exhaust and use it further to extract some useful work, decreasing the exhaust pollutants at the same time. Use of the Rankine Cycle, turbocharging and thermoelectric generation can be very useful as a waste heat recovery system.

Supercharging

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One way to increase engine power is to force more air into the cylinder so that more power can be produced from each power stroke. This can be done using some type of air compression device known as a supercharger, which can be powered by the engine crankshaft.

Supercharging increases the power output limits of an internal combustion engine relative to its displacement. Most commonly, the supercharger is always running, but there have been designs that allow it to be cut out or run at varying speeds (relative to engine speed). Mechanically driven supercharging has the disadvantage that some of the output power is used to drive the supercharger, while power is wasted in the high pressure exhaust, as the air has been compressed twice and then gains more potential volume in the combustion but it is only expanded in one stage.

Turbocharging

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A turbocharger is a supercharger that is driven by the engine's exhaust gases, by means of a turbine. A turbocharger is incorporated into the exhaust system of a vehicle to make use of the expelled exhaust. It consists of a two-piece, high-speed turbine assembly with one side that compresses the intake air, and the other side that is powered by the exhaust gas outflow.

When idling, and at low-to-moderate speeds, the turbine produces little power from the small exhaust volume, the turbocharger has little effect and the engine operates nearly in a naturally aspirated manner. When much more power output is required, the engine speed and throttle opening are increased until the exhaust gases are sufficient to 'spool up' the turbocharger's turbine to start compressing much more air than normal into the intake manifold. Thus, additional power (and speed) is expelled through the function of this turbine.

Turbocharging allows for more efficient engine operation because it is driven by exhaust pressure that would otherwise be (mostly) wasted, but there is a design limitation known as turbo lag. The increased engine power is not immediately available due to the need to sharply increase engine RPM, to build up pressure and to spin up the turbo, before the turbo starts to do any useful air compression. The increased intake volume causes increased exhaust and spins the turbo faster, and so forth until steady high power operation is reached. Another difficulty is that the higher exhaust pressure causes the exhaust gas to transfer more of its heat to the mechanical parts of the engine.

Rod and piston-to-stroke ratio

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The rod-to-stroke ratio is the ratio of the length of the connecting rod to the length of the piston stroke. A longer rod reduces sidewise pressure of the piston on the cylinder wall and the stress forces, increasing engine life. It also increases the cost and engine height and weight.

A "square engine" is an engine with a bore diameter equal to its stroke length. An engine where the bore diameter is larger than its stroke length is an oversquare engine, conversely, an engine with a bore diameter that is smaller than its stroke length is an undersquare engine.

Valve train

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The valves are typically operated by a camshaft rotating at half the speed of the crankshaft. It has a series of cams along its length, each designed to open a valve during the appropriate part of an intake or exhaust stroke. A tappet between valve and cam is a contact surface on which the cam slides to open the valve. Many engines use one or more camshafts "above" a row (or each row) of cylinders, as in the illustration, in which each cam directly actuates a valve through a flat tappet. In other engine designs the camshaft is in the crankcase, in which case each cam usually contacts a push rod, which contacts a rocker arm that opens a valve, or in case of a flathead engine a push rod is not necessary. The overhead cam design typically allows higher engine speeds because it provides the most direct path between cam and valve.

Valve clearance

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Valve clearance refers to the small gap between a valve lifter and a valve stem that ensures that the valve completely closes. On engines with mechanical valve adjustment, excessive clearance causes noise from the valve train. A too-small valve clearance can result in the valves not closing properly. This results in a loss of performance and possibly overheating of exhaust valves. Typically, the clearance must be readjusted each 20,000 miles (32,000 km) with a feeler gauge.

Most modern production engines use hydraulic lifters to automatically compensate for valve train component wear. Dirty engine oil may cause lifter failure.

Energy balance

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Otto engines are about 30% efficient; in other words, 30% of the energy generated by combustion is converted into useful rotational energy at the output shaft of the engine, while the remainder being lost due to waste heat, friction and engine accessories.[9] There are a number of ways to recover some of the energy lost to waste heat. The use of a turbocharger in diesel engines is very effective by boosting incoming air pressure and in effect, provides the same increase in performance as having more displacement. The Mack Truck company, decades ago, developed a turbine system that converted waste heat into kinetic energy that it fed back into the engine's transmission. In 2005, BMW announced the development of the turbosteamer, a two-stage heat-recovery system similar to the Mack system that recovers 80% of the energy in the exhaust gas and raises the efficiency of an Otto engine by 15%.[10] By contrast, a six-stroke engine may reduce fuel consumption by as much as 40%.

Modern engines are often intentionally built to be slightly less efficient than they could otherwise be. This is necessary for emission controls such as exhaust gas recirculation and catalytic converters that reduce smog and other atmospheric pollutants. Reductions in efficiency may be counteracted with an engine control unit using lean burn techniques.[11]

In the United States, the Corporate Average Fuel Economy mandates that vehicles must achieve an average of 34.9 mpg‑US (6.7 L/100 km; 41.9 mpg‑imp) compared to the current standard of 25 mpg‑US (9.4 L/100 km; 30.0 mpg‑imp).[12] As automakers look to meet these standards by 2016, new ways of engineering the traditional internal combustion engine (ICE) have to be considered. Some potential solutions to increase fuel efficiency to meet new mandates include firing after the piston is farthest from the crankshaft, known as top dead centre, and applying the Miller cycle. Together, this redesign could significantly reduce fuel consumption and NOx emissions.

Top dead center, before cycle begins 1 – Intake stroke 2 – Compression stroke
Starting position, intake stroke, and compression stroke.
Fuel ignites 3 – Power stroke 4 – Exhaust stroke
Ignition of fuel, power stroke, and exhaust stroke.

See also

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References

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General sources

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  • Hardenberg, Horst O. (1999). The Middle Ages of the Internal combustion Engine. Society of Automotive Engineers (SAE). ISBN 978-0-7680-0391-8.
  • scienceworld.wolfram.com/physics/OttoCycle.html
  • Cengel, Yunus A; Michael A Boles; Yaling He (2009). Thermodynamics An Engineering Approach. N.p. The McGraw Hill Companies. ISBN 978-7-121-08478-2.
  • Benson, Tom (11 July 2008). "4 Stroke Internal Combustion Engine". p. National Aeronautics and Space Administration. Retrieved 5 May 2011.
[edit]
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Four-stroke engine

View on Grokipedia
from Grokipedia
A four-stroke engine is an that completes a power cycle through four distinct strokes within the cylinder: , during which the piston moves downward to admit the air-fuel mixture; compression, where the piston rises to compress the mixture; power, in which ignition expands the combusted gases to drive the piston downward; and exhaust, expelling the spent gases as the piston rises again. This configuration requires two full revolutions per cycle, distinguishing it from two-stroke engines by enabling separate phases for and , which improves and reduces fuel waste. The cycle, formalized as the , was first successfully demonstrated in a practical by German Nikolaus August in 1876, building on theoretical principles outlined earlier by Alphonse Beau de Rochas in 1862 but achieving viable implementation through compressed charge ignition. Otto's design marked a pivotal advancement in reciprocating engines, supplanting less efficient predecessors and enabling widespread adoption in gasoline-powered vehicles, motorcycles, small aircraft, and generators due to its balance of power output, , and durability. Key characteristics include the use of poppet valves for precise timing of and exhaust, spark ignition for controlled in spark-ignition variants, and adaptability to both spark-ignition () and compression-ignition (Diesel) principles, though the four-stroke framework remains foundational for high-performance applications like automotive where emissions control and fuel economy are paramount. Despite competition from electric and alternative systems, four-stroke engines dominate global transportation, powering over 90% of light-duty vehicles as of recent assessments, underscoring their engineering robustness and scalability from single-cylinder lawnmower units to multi-cylinder V-configurations in high-output racing engines.

History

Invention and early development

The theoretical basis for the four-stroke cycle was first articulated by French engineer Alphonse Beau de Rochas, who patented the principle on January 16, 1862, outlining , compression, power, and exhaust strokes for improved efficiency in gas engines, though he constructed no working prototype. This concept built on earlier single-stroke designs like Étienne Lenoir's 1860 atmospheric engine but emphasized compression to enhance thermodynamic performance. German engineer Nikolaus August Otto pursued practical internal combustion engines from the early 1860s, initially developing a failed compressed-charge in 1861 and later partnering with Eugen Langen to produce a more efficient free-piston atmospheric engine in 1864. By 1876, at the Gasmotoren-Fabrik Deutz in , Otto engineered the first viable four-stroke engine, achieving its initial successful run in early March of that year; this compressed-charge design operated on , delivering about 3 horsepower at 180 RPM with significantly higher —around 12-15%—compared to prior engines' 4%. The engine featured a horizontal single-cylinder configuration with slide valves and electric ignition, patented later in 1876 after resolving challenges. Early development focused on stationary applications for factories and farms, with Deutz producing over 50 units by 1884, incorporating refinements like improved carburetion for liquid fuels. Otto's innovation displaced steam engines in many low-power uses due to its compact size, lower fuel consumption, and elimination of boilers, though initial models suffered from low speed and vibration issues addressed in subsequent iterations. Legal disputes over the , including claims referencing Beau de Rochas' work, were ultimately upheld in Otto's favor in , enabling widespread licensing across .

Key thermodynamic cycles

The serves as the ideal thermodynamic model for spark-ignition four-stroke engines, consisting of four processes: isentropic compression from bottom dead center to top dead center, constant-volume heat addition via spark ignition, isentropic expansion driving the downward, and constant-volume heat rejection during exhaust. This cycle approximates the operation of gasoline engines, where fuel-air mixture is compressed to a ratio typically between 8:1 and 12:1 before ignition to avoid autoignition knock. The of the ideal Otto cycle is given by η = 1 - (1/r)^{γ-1}, where r is the and γ ≈ 1.4 for air-fuel mixtures; higher r increases efficiency but is limited by material strength and risks. In contrast, the Diesel cycle models compression-ignition four-stroke engines, featuring isentropic compression, constant-pressure heat addition as fuel injects into hot compressed air, isentropic expansion, and constant-volume heat rejection. Diesel engines achieve compression ratios of 14:1 to 25:1, enabling higher efficiencies through greater expansion work extraction without pre-ignition issues, though for identical r, Otto efficiency exceeds Diesel due to earlier heat addition timing. The ideal Diesel efficiency formula is η = 1 - (1/r)^{γ-1} \cdot \frac{ρ^γ - 1}{γ(ρ - 1)}, with ρ as the cutoff ratio (volume at end of heat addition over compressed volume); real Diesel engines convert 35-45% of fuel energy to work, outperforming Otto's 25-30% under practical loads. Variations like the modify the process for improved efficiency in four-stroke engines, particularly hybrids, by extending the expansion stroke beyond the compression stroke via late valve closure, reducing pumping losses but sacrificing . Patented in 1882, modern implementations in engines like Toyota's Prius achieve effective expansion ratios up to 1.5 times the geometric , yielding efficiencies 5-10% higher than standard at part loads through over-expansion. The , a supercharged Atkinson variant, further boosts air to compensate for volumetric inefficiency.

Commercial adoption and engineering milestones

Following the successful demonstration of Nikolaus Otto's four-stroke engine in March 1876, commercial production commenced at N.A. Otto & Cie (later ) for stationary applications, where the engines powered industrial machinery, gas works, and early electric generators using as fuel. These low-speed, large-displacement units, typically single-cylinder, achieved widespread adoption in by the early due to their superior efficiency over prior atmospheric engines. Engineering adaptations for higher speeds enabled vehicular use; in 1885, and developed a compact, high-revving four-stroke engine producing 0.5 horsepower at 900 rpm for Daimler's Reitwagen , marking the first mobile application. The following year, Karl Benz installed a similar single-cylinder four-stroke unit (954 cc, 0.75 horsepower) in his Patent-Motorwagen, patented on January 29, 1886, recognized as the first practical automobile. This transition from stationary to transport roles spurred rapid commercialization, with Benz producing about 25 units by 1893. Key milestones included multi-cylinder designs for smoother operation; Wilhelm Maybach constructed the first production four-cylinder four-stroke engine in 1890 for Daimler applications. Valve train advancements followed, with overhead (OHC) configurations appearing in 1902 on the Marr Auto Car's , allowing higher revs and better breathing. Overhead valve (OHV) pushrod systems, patented in 1902 by Buick engineer Eugene Richard (awarded 1904), improved efficiency in mass-produced engines like the 1904 Ford Model B, Ford's first four-cylinder offering. Aviation adoption accelerated development; the ' 1903 Flyer featured a custom inline four-cylinder four-stroke engine delivering 12 horsepower, enabling the first powered flight on December 17, 1903. By the , four-stroke engines dominated automotive production, exemplified by the 1908 Ford Model T's 177 ml inline-four, which facilitated mass adoption with over 15 million units built until 1927, transforming personal transport. These advancements in cylinder configuration, geometry, and established the four-stroke cycle as the foundational technology for internal combustion through the mid-20th century.

Operating Principle

The four strokes

The four-stroke cycle of a reciprocating internal combustion engine comprises intake, compression, power, and exhaust strokes, executed over two full crankshaft revolutions to convert chemical energy in fuel into mechanical work. This sequence ensures separation of gas exchange and combustion processes, enabling higher efficiency compared to two-stroke designs by reducing short-circuiting of fresh charge with exhaust gases. In spark-ignition engines operating on the Otto cycle, the process begins with the piston at top dead center (TDC). Intake stroke: The descends from TDC to bottom dead center (BDC) while the valve opens, creating a partial that draws the air-fuel mixture into the through the intake port. The valve remains closed during the subsequent strokes to isolate the contents. , typically 80-90% in naturally aspirated engines, determines the mass of charge inducted, influenced by manifold design and position. Compression stroke: With both valves closed, the piston rises from BDC to TDC, compressing the air-fuel mixture to increase its temperature and pressure, preparing it for ignition. Compression ratios in gasoline engines range from 8:1 to 12:1, balancing efficiency gains against knock propensity. The work input during this stroke is recovered partially in the expansion phase, per the Otto cycle thermodynamics. Power stroke: Near TDC, the ignites the compressed mixture, causing rapid that elevates pressure to 50-100 bar, forcing the downward to BDC and delivering to the via the . This expansion stroke produces the net positive work of the cycle, with peak pressures occurring 10-15 degrees after TDC for optimal . In diesel four-stroke engines, ignition occurs via compression heating without a spark, accommodating higher ratios up to 20:1. Exhaust stroke: The piston ascends from BDC to TDC with the exhaust open, expelling products through the exhaust port to the manifold. Residual exhaust gas fraction, around 5-10%, affects subsequent cycle efficiency and emissions. Valve overlap—brief simultaneous opening of and exhaust valves near TDC—scavenges residuals and initiates , tuned via phasing for specific engine speeds. The cycle repeats, with timing controlled by the synchronized to rotation at half speed.

Cycle variations and mechanics

The governs the operation of most spark-ignition four-stroke engines, featuring isentropic compression followed by constant-volume heat addition via spark ignition, isentropic expansion, and constant-volume heat rejection. This cycle achieves thermal efficiencies typically around 30% in practical applications due to limitations in compression ratios, limited to 8:1 to 12:1 to avoid knocking. In contrast, the applies to compression-ignition four-stroke engines, where heat addition occurs at constant pressure after high compression ratios of 14:1 to 25:1, enabling auto-ignition of without spark. This configuration yields higher thermal efficiencies, often exceeding 40% in heavy-duty variants, as the greater extracts more work from gases before exhaust. The , patented by James Atkinson in 1882, deviates from the by extending the expansion stroke relative to compression through delayed intake valve closure, which reduces effective compression volume and pumping losses while preserving a longer power stroke for improved thermodynamic efficiency. Modern engines achieve this via , operating in Atkinson mode under light loads for fuel economy gains of up to 10-15% over standard cycles, though at reduced output. The , introduced by in 1957, employs early or late intake valve closing combined with supercharging to limit trapped air mass during compression, mimicking Atkinson's expansion advantage while compensating for power loss through . This results in elevated expansion ratios and efficiencies approaching those of Atkinson designs, particularly in boosted applications, with shifts altering the intake event to refrigerate the charge and lower peak temperatures.

Thermodynamic Analysis

Ideal vs. real cycle efficiency

The ideal , which models the four-stroke under air-standard assumptions, posits reversible adiabatic compression and expansion processes, instantaneous constant-volume heat addition during , and constant-volume heat rejection, with the as an exhibiting constant specific heats. These assumptions yield a of η=1−1rγ−1\eta = 1 - \frac{1}{r^{\gamma-1}}, where rr is the volumetric and γ≈1.4\gamma \approx 1.4 is the ratio of specific heats for air. For practical compression ratios of 8 to 12 in engines—limited by knock to avoid auto-ignition—this formula predicts efficiencies of approximately 56% to 60%. Real four-stroke engines achieve brake thermal efficiencies of 25% to 35% for gasoline spark-ignition variants and up to 40% to 45% for compression-ignition diesel types, reflecting substantial deviations from ideal conditions due to irreversibilities, non-ideal gas behavior, and parasitic losses. Indicated thermal efficiency, measured at the crankshaft before mechanical deductions, reaches 35% to 40% in optimized spark-ignition engines but is eroded by factors such as variable specific heats (reducing effective γ\gamma to below 1.3 at combustion temperatures exceeding 2000 K), chemical dissociation of combustion products, and incomplete fuel-air mixing. Key losses include heat transfer to cylinder walls and coolant (20% to 30% of fuel energy, exacerbated by finite combustion duration and surface-area-to-volume ratios), mechanical friction from piston rings, bearings, and valvetrain (5% to 10% penalty on indicated work), and pumping work during throttled intake and exhaust strokes (up to 10% at part load in spark-ignition engines). Additional reductions stem from blow-by gases escaping past rings (1% to 3% fuel loss), incomplete combustion (2% to 5% at low loads), and exhaust residuals diluting the charge. Diesel cycles benefit from higher compression ratios (14 to 22), approaching ideal efficiencies closer to 65%, but still incur analogous losses scaled by their constant-pressure heat addition.
Loss MechanismTypical Magnitude (% of Fuel Energy)Primary Cause
Heat transfer20–30Conduction to walls during finite-rate and expansion
Mechanical friction5–10Viscous drag in lubricated contacts, valvetrain inertia
Pumping5–10 (part load)Throttling and backpressure in /exhaust
Incomplete combustion/blow-by3–8Finite mixing, crevice volumes, ring leakage
These disparities underscore that while the ideal cycle provides a thermodynamic benchmark, real efficiency is constrained by material limits, , and , with advancements like and turbocharging mitigating but not eliminating the gap.

Losses and performance factors

In real four-stroke engines operating on the , efficiency deviates from the ideal thermodynamic prediction due to several irreversible losses, primarily frictional dissipation, gas pumping work, to surroundings, and incomplete . Frictional losses arise from mechanical interactions such as piston ring-cylinder wall contact, crankshaft bearings, and valve train components, consuming 5-15% of indicated power depending on engine speed and load; these increase quadratically with rotational speed due to viscous drag and account for higher specific fuel consumption at elevated RPMs. Pumping losses, unique to four-stroke cycles, stem from the net work required for and exhaust strokes, exacerbated in spark-ignition engines by to control load, which creates a sub-atmospheric pressure and positive exhaust backpressure, resulting in a negative loop on the pressure-volume diagram that can consume up to 10-20% of gross indicated work at part . losses occur via and from hot combustion gases to walls, crowns, and heads, with rates peaking during the power stroke; these typically dissipate 20-30% of , influenced by thermal boundary layers and metal temperatures around 500-600 , reducing the effective . Additional losses include blow-by gases escaping past piston rings into the crankcase (1-5% of intake charge) and incomplete combustion from finite flame speeds and quench layers near walls, leading to unburned hydrocarbons and chemical energy losses in exhaust (5-10% of fuel input). Performance factors mitigating these include higher compression ratios (typically 8:1 to 12:1 in gasoline engines), which boost thermal efficiency per the relation η = 1 - (1/r)^{γ-1} (where γ ≈ 1.4 for air-fuel mixtures) by expanding gases closer to adiabatic conditions, though limited by autoignition knock to avoid pre-ignition. Optimized air-fuel ratios near stoichiometric (14.7:1 for gasoline) minimize incomplete combustion, while advanced ignition timing advances peak pressure for better work extraction, and longer stroke-to-bore ratios reduce relative heat transfer surface area, enhancing efficiency by 2-5% in opposed-piston designs. Variable valve timing reduces pumping losses by 5-10% at part loads through late intake valve closing, akin to Atkinson cycle extensions. Overall, these factors yield brake thermal efficiencies of 25-35% in modern automotive four-stroke engines under optimal conditions, far below the 60% ideal Otto limit at r=10.

Design and Engineering Principles

Core components and assembly

The cylinder block serves as the foundational structure of a four-stroke engine, typically from , housing the cylinders where pistons reciprocate and supporting the via main bearings. It integrates the below the cylinders to contain lubricating oil and often includes coolant passages for thermal management. Pistons, usually constructed from lightweight aluminum alloys, fit snugly within the cylinders and are equipped with rings to seal gases, scrape from walls, and facilitate heat transfer. Each piston connects to a via a wrist pin, allowing pivotal motion, while the rod's lower end attaches to the crankshaft throw with a bearing for high-load . Forged connecting rods transmit the explosive forces from , converting the piston's into the crankshaft's rotary output. The , forged from high-strength steel with counterweights for balance, rotates within the block's main bearings, transforming reciprocating forces into for propulsion. The , bolted atop the block with a for sealing, encloses the and houses elements including intake and exhaust valves. These valves, made of heat-resistant alloys, control charge admission and exhaust expulsion, held closed by coil springs against machined seats. Assembly begins with installing the into the cylinder block's bearings, followed by attaching connecting rods to its throws. Pistons, fitted with rings and pinned to rods, are then inserted into and secured to the . The is positioned with a multi-layer or composite and torqued to specifications, integrating ports for , exhaust, and spark ignition. The valvetrain assembly varies by configuration: in overhead valve (OHV) designs, the camshaft mounts in the block, actuating valves via lifters, pushrods, and rocker arms in the head; overhead cam (OHC) places the directly in the head for shorter, stiffer paths using tappets or finger followers. The , driven by timing chain or belt from the at half speed, profiles lobe shapes to dictate , lift, and duration essential for efficient four-stroke operation. Precision alignment during assembly ensures synchronization, preventing valve-piston interference.

Valve train and timing systems

The valve train, also known as the , comprises the mechanical assembly responsible for opening and closing the and exhaust in a four-stroke engine to regulate the admission of the air-fuel mixture and expulsion of gases. Core components include the , which features eccentrically shaped lobes that dictate valve lift and duration; cam followers or tappets that transmit motion from the ; pushrods and rocker arms in certain configurations; typically made of high-strength steel or alloys; coil springs to return to their seats; and hydraulic lash adjusters or solid lifters to maintain precise clearance. These elements ensure operate in synchrony with the , with the driven at half speed via a timing chain, belt, or gears to match the four-stroke cycle. Valve train architectures vary by camshaft placement relative to the valves. In overhead valve (OHV) designs, also termed pushrod engines, the camshaft resides in the engine block, actuating valves in the cylinder head via pushrods and rocker arms; this configuration offers compact head design, lower production costs, and superior low-speed torque due to optimized leverage, though it incurs higher inertial mass limiting maximum engine speeds to around 6,000-7,000 rpm. Overhead camshaft (OHC) systems position the camshaft in the head for direct or near-direct valve actuation, subdivided into single overhead camshaft (SOHC) for both intake and exhaust valves or dual overhead camshaft (DOHC) with separate cams per valve type; OHC variants enable higher rev limits exceeding 8,000 rpm, improved airflow via straighter ports, and potential for four valves per cylinder, albeit at increased complexity and cost. DOHC engines, common in high-performance applications since the 1980s, facilitate independent control of intake and exhaust phasing for enhanced across rpm ranges. Timing systems govern the precise phasing of valve events relative to piston position, with intake valves typically opening 10-20° before top dead center (BTDC) on the stroke and closing 40-70° after bottom dead center (ABDC), while exhaust valves open 40-70° before bottom dead center (BBDC) on the power stroke and close 10-20° after top dead center (ATDC) to optimize filling and scavenging without excessive overlap that risks charge dilution. Fixed timing suits basic engines but compromises efficiency; (VVT) addresses this by dynamically adjusting phase, lift, or duration using mechanisms like vane-type phasers actuated by engine oil pressure or electric motors, improving low-end by up to 10-15% and fuel economy by 5-10% via optimized timing maps. Pioneered in production by Alfa Romeo's Twin Cam in the for mechanical advance and refined electronically in Honda's system introduced in 1989, VVT has proliferated, with systems like BMW's (1992) and Toyota's (1996) demonstrating causal links to broader power bands and reduced emissions through better combustion control.

Boosting and airflow optimization

Forced induction, commonly referred to as boosting, enhances the power output of four-stroke engines by elevating intake manifold pressure above atmospheric levels, thereby increasing the mass of air (and consequently fuel) per cycle. This is achieved through devices that compress incoming air, with turbochargers utilizing exhaust gas energy to drive a turbine-linked compressor, recovering otherwise wasted thermal energy from the exhaust stream. Superchargers, in contrast, are mechanically driven by the engine crankshaft via belts or gears, providing immediate boost response without reliance on exhaust flow but incurring direct parasitic power losses typically ranging from 10 to 20 percent of engine output. In diesel four-stroke engines, turbocharging is particularly prevalent due to their higher exhaust temperatures and compression ratios, enabling boost pressures up to 3-4 bar in modern heavy-duty applications, which can yield brake thermal efficiencies exceeding 45 percent under optimized loads. Turbocharger efficiency hinges on matching and maps to operating conditions, with advancements like variable geometry turbines (VGT) adjusting vane angles to reduce lag and broaden the curve across RPM ranges. For instance, VGT systems in automotive diesels can minimize turbo lag to under 0.5 seconds at low speeds while preventing overboost at high loads, improving by up to 30 percent compared to fixed-geometry units. Twin-scroll turbochargers further optimize airflow by separating exhaust pulses from banks, preserving and enhancing low-end by 15-20 percent in inline-four s. Superchargers, often positive displacement types like or compressors, excel in high-RPM power delivery for spark-ignition s, as seen in applications achieving 50 percent power increases without intercooling, though they demand robust internals to withstand risks from elevated charge temperatures. Airflow optimization complements boosting by minimizing restrictions and maximizing , defined as the ratio of actual air mass ingested to the theoretical maximum. In naturally aspirated or boosted four-stroke cycles, manifold runner length and diameter are tuned for inertial ram charging via , where optimal lengths (typically 20-40 cm for automotive engines) align pressure waves to augment cylinder filling at target RPMs, potentially boosting by 5-10 percent. Variable-length manifolds, employing rotary valves or sliders, switch geometries to adapt across engine speeds; for example, systems in production gasoline engines extend runners at low RPM for and shorten them at high RPM for power, achieving up to 12 percent gains in bandwidth. Valve timing optimization via variable valve timing (VVT) systems, such as cam phasers or multi-profile cams, dynamically adjusts intake valve closing to exploit the Atkinson-like cycle for efficiency or Otto cycle for power, reducing pumping losses by 5-7 percent in boosted setups. Intercoolers, or charge air coolers, are integral to boosted airflow management, densifying compressed air by 10-15 percent per 50°C temperature drop, mitigating knock in gasoline engines and enabling higher boost levels without efficiency penalties from excessive heat. Exhaust manifold design, including log-style versus tubular headers, further aids boosting by equalizing pulse timing, with tuned exhaust systems recovering 2-5 percent of energy for turbo drive while optimizing backpressure to under 1.2 times intake pressure. Overall, integrated boosting and airflow strategies can elevate specific power output to over 100 kW/L in downsized engines, though they introduce challenges like increased thermal stresses requiring materials such as Inconel alloys for durability.

Structural ratios and durability

The bore-to-stroke ratio in four-stroke engines defines the relative dimensions of the bore to the stroke length, influencing mechanical stresses, , and operational limits. Oversquare configurations (bore exceeding stroke) reduce for a given rotational speed, mitigating inertial loads on reciprocating components and enhancing high-RPM durability by lowering peak accelerations. Undersquare designs (stroke exceeding bore), common in torque-oriented applications, elevate —calculated as 2×stroke×RPM/602 \times \text{stroke} \times \text{RPM} / 60 in meters per second—potentially accelerating through increased side and bearing forces, though they favor low-end power. Empirical studies identify an optimal bore-to-stroke ratio near 0.93 for balancing power output, , and emissions while preserving structural integrity under cyclic combustion pressures. The length-to-stroke ratio further modulates durability by governing angulation relative to the wall. Ratios above 1.5 (longer rods) minimize lateral thrust forces during the compression and power strokes, reducing skirt scuffing, wall abrasion, and demands, thereby extending in high-load scenarios. Lower ratios amplify these side loads due to greater rod angularity, increasing frictional losses and fatigue risks in rings and liners, particularly in stroker modifications where stroke extensions without proportional rod lengthening degrade wear resistance. This geometric factor interacts with limits, conventionally capped at 20-25 m/s for automotive durability to avoid excessive inertial stresses on the and bearings, with modern forged components permitting up to 30 m/s in contexts before reliability declines. Overall engine durability hinges on these ratios' integration with and finite element of the block and head, where thin-wall cast aluminum designs demand precise stress distribution to resist from peak pressures exceeding 100 bar. Cyclic loading from induces in critical junctions like caps, with ratios optimizing load paths to achieve 200,000-500,000 km lifespans in passenger vehicle applications under standard duty cycles. Advanced simulations confirm that deviations from balanced ratios exacerbate harmonics, accelerating crack in high-mileage operation absent robust .

Fuel and Combustion

Fuel types and compatibility

Four-stroke engines operate using either spark-ignition or compression-ignition principles, with fuel types tailored to each mechanism. Spark-ignition variants predominantly utilize , a volatile mixture refined to specific ratings (typically 87-93 AKI for automotive applications) to prevent under compression ratios of 8:1 to 12:1. , consisting of heavier s with cetane numbers of 40-55, powers compression-ignition four-stroke engines, which achieve ratios of 14:1 to 25:1, relying on auto-ignition from rather than sparks. Cross-compatibility is absent; injecting diesel into a gasoline engine fails to ignite without a spark and risks injector clogging, while in a causes incomplete and potential hydraulic lock from low . Gasoline engines exhibit broad compatibility with ethanol blends up to E10 (10% ethanol by volume), as evidenced by manufacturer certifications for unleaded fuels meeting ASTM D4814 standards, though higher blends like E15 or demand corrosion-resistant materials (e.g., fuel lines) and recalibrated fuel systems to mitigate and . Small engines, such as those in lawn mowers or outboards, perform optimally on ethanol-free to avoid hygroscopic ethanol attracting water, leading to in carburetors and reduced . Diesel engines tolerate biodiesel blends up to B20 (20% fatty acid methyl esters) without significant modifications, provided fuels meet ASTM D975 specifications, but higher percentages increase emissions and require upgraded seals to counter solvent effects. Alternative fuels like , , and offer potential for four-stroke engines but necessitate engine redesigns for compatibility. Methanol, with its high octane (108-110) and oxygen content, suits dual-fuel or dedicated spark-ignition setups, enabling operation but demanding larger fuel tanks due to lower (20 MJ/kg vs. 44 MJ/kg for ) and anti-corrosion additives. Compressed (CNG) or (LPG) integrates via port injection in engines, reducing CO2 by 20-30% but requiring high-pressure storage and timing adjustments for slower flame speeds. in modified four-strokes yields zero carbon emissions but poses challenges from high flame speeds causing backfiring and the need for reinforced pistons against . Biofuels and synthetic e-fuels expand options, yet empirical tests confirm that unmodified engines risk durability loss from altered and , underscoring the primacy of petroleum-derived fuels for standard applications.

Ignition and combustion processes

In spark-ignition four-stroke engines operating on the , ignition occurs near the end of the compression stroke when the delivers a high-voltage electrical discharge across its electrodes, creating a plasma kernel that initiates of the premixed air-fuel charge. This spark is timed to fire typically 10 to 40 degrees of crankshaft rotation before top dead center (BTDC), allowing the process to begin while the is still rising, thereby maximizing development during the subsequent power stroke. Advancing the increases peak cylinder and output by aligning heat release more closely with the expansion stroke, though excessive advance risks engine knock due to auto-ignition of end gases. Combustion proceeds as the initial kernel expands rapidly, transitioning from laminar to turbulent influenced by in-cylinder flow structures such as swirl and tumble, with speeds reaching 20 to 50 meters per second under typical operating conditions. The process approximates constant-volume heat addition in the ideal , where chemical energy release elevates temperatures to approximately 2,000–2,500 K and pressures to 50–100 bar, driving the downward and converting into mechanical work. Incomplete or misfires can occur if the air-fuel ratio deviates significantly from stoichiometric (around 14.7:1 for ), with lean mixtures slowing and rich mixtures quenching the front. Turbulence generated by intake flow and piston motion enhances mixing and flame area, accelerating burn rates and reducing combustion duration to 1–2 milliseconds at wide-open throttle, but excessive turbulence can entrain unburned hydrocarbons into crevices, contributing to cycle-to-cycle variability in burn efficiency. Ignition timing optimization, often via electronic control units adjusting for load, speed, and temperature, balances power, efficiency, and emissions; for instance, retarding timing by 5–10 degrees reduces peak temperatures and NOx formation while potentially increasing hydrocarbon emissions from slower, cooler burns. In diesel four-stroke variants, ignition relies on compression-induced auto-ignition rather than spark, with fuel injected directly into high-temperature air (above 700 K at 15–20:1 compression ratios), leading to stratified diffusion flames rather than premixed propagation.

Emissions formation and mitigation

In four-stroke spark-ignition engines, the primary exhaust emissions consist of unburned hydrocarbons (HC), carbon monoxide (CO), nitrogen oxides (), and particulate matter (PM), with (CO2) as a combustion byproduct. These form mainly during the power stroke, where incomplete or high-temperature reactions in the deviate from ideal fuel oxidation. HC arises from quenching at cold cylinder walls, crevice entrapment of fuel-air mixture, and incomplete vaporization of fuel droplets, leading to unburned fuel exiting via the exhaust stroke. CO results from oxygen-deficient local zones in the , where fuel partially oxidizes to CO rather than fully to CO2 due to insufficient mixing or short residence times at high temperatures. NOx formation predominantly occurs via the thermal Zeldovich mechanism, where atmospheric nitrogen (N2) and oxygen (O2) react at peak combustion temperatures exceeding 1800 K (about 1500°C), producing nitric oxide (NO) that partially converts to NO2 post-combustion; supplemental pathways include prompt NOx from hydrocarbon radicals and fuel-bound nitrogen, though the latter is minimal in typical gasoline. PM, primarily in direct-injection variants, stems from rich fuel zones forming soot precursors during diffusion flames, though levels remain lower than in diesel engines due to premixed combustion dominance. Mitigation strategies integrate in-cylinder controls and aftertreatment. Precise air-fuel ratio (AFR) management near (14.7:1 for ) via electronic fuel injection minimizes HC and CO by ensuring sufficient oxygen for oxidation while avoiding excess air that quenches flames. (EGR) dilutes intake charge with 5-15% recirculated exhaust, lowering peak combustion temperatures by 200-300 K to suppress via reduced O2 availability and specific heat increase, though it can elevate HC and CO if unoptimized. Three-way catalytic converters, standard since the , achieve over 90% simultaneous reduction of CO (to CO2), HC (to CO2 and H2O), and (to N2) under closed-loop AFR control using oxygen sensors; they employ , , and on monoliths to facilitate reactions at 400-800°C. Advanced variants include close-coupled positioning for faster light-off and particulate filters for direct-injection engines to trap PM, oxidizing it via additives. Lean-burn configurations with adsorbers or (SCR) further enable efficiency gains but require urea injection for hydrolysis in diesel-like applications.

Applications and Performance

Automotive and transportation uses

The four-stroke engine has been the predominant powerplant in passenger automobiles since Karl Benz fitted a single-cylinder four-stroke engine to his Patent-Motorwagen in 1886, marking the first practical automobile. This design, based on Nikolaus Otto's 1876 cycle, enabled reliable operation with compression ratios yielding thermal efficiencies up to 30% in modern variants. By the early , multi-cylinder four-stroke engines powered mass-produced vehicles like the starting in 1908, establishing the as the standard for personal transportation due to its balance of and fuel economy. Today, nearly all -powered passenger cars employ four-stroke Otto-cycle engines, with market projections indicating internal combustion propulsion, predominantly four-stroke, retaining about 41.8% revenue share in passenger vehicles as of amid trends. In commercial transportation, four-stroke diesel engines dominate heavy-duty trucks and buses for their superior and efficiency from higher compression ratios, typically 14:1 to 22:1. These engines, operating on the four-stroke invented by in 1892, power the majority of global freight and public transit fleets, with virtually 100% of European diesel trucks using four-stroke configurations featuring turbocharging and direct injection. Diesel four-strokes achieve better fuel economy than counterparts, contributing to their prevalence in applications requiring long-haul durability, though they produce higher emissions necessitating aftertreatment systems. In the United States, medium- and heavy-duty trucks rely on four-stroke diesels from manufacturers like and , supporting logistics that move over 70% of freight by ton-miles. Four-stroke engines have increasingly supplanted two-strokes in , particularly since the , driven by stricter emissions regulations and demands for smoother power delivery. Yamaha's YZ400F in 1998 pioneered competitive four-stroke bikes, leading to widespread adoption where four-strokes now constitute the standard for off-road and street models due to reduced oil consumption and lower unburnt emissions. Modern four-stroke engines, often liquid-cooled and , offer power outputs from 50 to over 200 horsepower in sport variants, with global market growth projected at 4.1% to 6.1% CAGR through 2034, largely featuring four-stroke designs. This shift reflects the four-stroke's inherent efficiency advantage, consuming only every other compared to two-strokes, resulting in up to 50% better economy in equivalent displacements.

Industrial and marine implementations

Four-stroke engines are extensively employed in industrial settings for stationary power generation, where variants predominate and achieve capacities up to 18 MW per unit, supporting combined heat and power systems with high reliability for continuous operation. Diesel models from manufacturers like provide ratings from 429 to 597 kW (575 to 800 hp) at 1800–2000 rpm, powering applications in oil and gas extraction, pipeline transport, and emergency backup generators, valued for their durability under variable loads. These engines often feature inline or V configurations, with displacements ranging from 4.4 L in compact units like the C4.4 (up to 150 kW) to larger 18 L blocks for heavy-duty tasks in and . In marine environments, four-stroke engines serve primarily as medium-speed and sources, offering power outputs from 221 kW to over 10 MW, suitable for ferries, supply vessels, and offshore support ships where quieter operation and lower emissions relative to two-strokes are advantageous. The 31, recognized for peak thermal efficiency exceeding 50% in its class, delivers 4.6–10.4 MW across 8- to 16- configurations at 720–750 rpm, enabling flexibility including diesel and dual-fuel options for reduced lifecycle costs. Similarly, MAN's L27/38 series provides 2.1–3.69 MW for , emphasizing long overhaul intervals and adaptability to heavy fuels. Overall marine four-stroke power spans 2 kW to 25 MW, with inline-6 to V-20 layouts optimized for control and compliance with emission standards like IMO Tier III.

Power output and efficiency metrics

Brake mean effective pressure (BMEP) serves as a key metric for assessing power output in four-stroke engines, representing the average effective pressure on the that yields the measured brake power for a given displacement. For naturally aspirated four-stroke engines, BMEP typically ranges from 8 to 12 bar, while turbocharged variants achieve 15 to 25 bar or higher in optimized designs, enabling specific power outputs exceeding 100 horsepower per liter in modern automotive applications. Diesel four-stroke engines exhibit comparable or slightly higher BMEP values, often 15 to 25 bar under boost, reflecting their capacity for sustained high-pressure combustion. Brake thermal efficiency (BTE), the ratio of brake work output to fuel energy input, quantifies fuel conversion effectiveness in four-stroke cycles. four-stroke engines achieve BTE of 25% to 40%, with downsized turbocharged models reaching 35% to 40% through elevated compression ratios (up to 12:1 or more), direct injection, and that minimize pumping losses and enable operation. Diesel counterparts attain 35% to 45% BTE, benefiting from compression ratios of 16:1 to 20:1 and inherently higher expansion ratios that extract more work from combustion heat. Advanced prototypes, incorporating technologies like modifications or exhaust heat recovery, have demonstrated BTE exceeding 45% in both fuel types under controlled conditions. Brake specific fuel consumption (BSFC), expressed in grams of fuel per , inversely correlates with efficiency and highlights operational economy. Four-stroke spark-ignition engines yield BSFC around 250 g/kWh at peak , whereas compression-ignition variants achieve approximately 200 g/kWh, underscoring diesel's superior part-load due to lower heat rejection and reduced throttling. These metrics improve with load, as BSFC minima occur near maximum where and completeness peak.
MetricGasoline Four-Stroke (Typical)Diesel Four-Stroke (Typical)
Brake Thermal Efficiency (%)25–4035–45
BSFC (g/kWh)~250~200
BMEP (bar, turbocharged)15–2515–25
Empirical data from testing confirm these ranges, though real-world variability arises from factors like air-fuel ratio, , and mean effective pressure (FMEP), which deducts 1–3 bar from indicated values in high-speed operation.

Advantages and Comparisons

Benefits over two-stroke engines

Four-stroke engines demonstrate higher than two-stroke engines primarily because their cycle dedicates separate strokes to and exhaust, enabling more complete trapping of the air-fuel charge and reducing scavenging losses where fresh mixture escapes unburned in two-stroke designs. This results in lower (BSFC), with four-stroke engines typically achieving thermal efficiencies 10-20% higher under comparable loads due to optimized and reduced pumping losses. In practical applications like outboard motors, four-stroke variants consume up to 50% less fuel at cruising speeds compared to carbureted two-strokes of similar displacement. Emissions from four-stroke engines are substantially lower, as they avoid the oil-fuel premixing required in two-strokes, which leads to incomplete combustion and elevated hydrocarbons (HC), carbon monoxide (CO), and particulate matter (PM). Two-stroke engines can emit approximately 10 times more pollutants per unit of power output due to inherent loop-scavenging inefficiencies that allow oil and unburned fuel to exit via the exhaust port. Comparative testing of spark-ignition engines confirms that four-strokes, especially with aftertreatment like catalytic converters, reduce HC and CO by 50-90% relative to unmodified two-strokes. Durability advantages stem from the four-stroke's pressurized system, which delivers independently of , ensuring consistent film strength on bearings, pistons, and cylinders even under varying loads—contrasting with two-strokes' reliance on volatile premixed that evaporates or dilutes unevenly, accelerating . This separation allows four-strokes to operate reliably for 2,000-5,000 hours before major overhaul in industrial uses, versus 500-1,000 hours for high-performance two-strokes, with reduced risks of from lubrication failure. Additionally, four-strokes provide smoother delivery and lower through even firing intervals, enhancing component longevity in prolonged duty cycles. Overall, these attributes make four-strokes preferable for applications demanding sustained operation, such as automotive and , where two-strokes' higher power density is offset by demands and regulatory restrictions on emissions.

Empirical comparisons to electric motors

Four-stroke internal engines (ICEs) typically achieve efficiencies of 25-40% in modern automotive applications, limited by thermodynamic constraints such as losses and incomplete , whereas electric motors convert over 90% of electrical input to mechanical output under optimal conditions. Well-to-wheel (WTW) efficiencies for four-stroke ICE vehicles range from 11-27%, reflecting upstream production losses, while electric vehicles (EVs) can reach 50-70% WTW when powered by efficient grids, though this drops significantly with coal-heavy mixes. In terms of power and torque delivery, electric motors provide maximum instantaneously from zero RPM due to their electromagnetic design, enabling superior low-speed acceleration without multi-gear transmissions, whereas four-stroke ICEs require RPM buildup to peak , often necessitating gearboxes for optimal performance across speed ranges. Gasoline's volumetric of approximately 12,700 Wh/kg vastly exceeds that of lithium-ion batteries at 200-300 Wh/kg, allowing ICE vehicles lighter storage for equivalent range, though EVs compensate partially through higher . Lifecycle greenhouse gas emissions analyses indicate EVs generally emit 50-70% less CO2 equivalent over their full lifecycle compared to gasoline four-stroke vehicles in regions with moderate grid decarbonization, but upfront battery manufacturing emissions—equivalent to 20,000-50,000 km of driving—can offset benefits in coal-dependent grids or short vehicle lifespans. Maintenance costs for EVs average 6.1 cents per mile versus 10.1 cents for vehicles, driven by fewer moving parts and no oil changes, though EV repairs can exceed costs by 30% when involving high-voltage components. Refueling a four-stroke takes 3-5 minutes for a full , compared to 20-60 minutes for 80% EV fast-charging sessions, limiting EV practicality for long-distance travel without extensive .

Environmental Considerations and Debates

Factual emissions profile

Four-stroke engines, whether spark-ignition (typically gasoline-fueled) or compression-ignition (typically diesel-fueled), emit exhaust gases dominated by (CO₂), (H₂O), (N₂), and residual oxygen (O₂), which account for approximately 99.5–99.9% of the molar exhaust content under stoichiometric or conditions. These major components arise from the oxidation of fuel hydrocarbons and atmospheric air during , with CO₂ formed via complete carbon oxidation and H₂O from hydrogen-oxygen reactions. Key pollutants include (CO) from incomplete carbon oxidation, unburned hydrocarbons (HC) or non-methane organic gases (NMOG) from fuel evaporation and incomplete , oxides () from high-temperature reactions between atmospheric and oxygen, and particulate matter (PM), which consists largely of (elemental carbon) with adsorbed organics in . In gasoline four-stroke engines, PM emissions are minimal without direct injection, typically averaging 3–12 mg per mile under driving cycles like FTP, while diesel four-stroke engines produce higher PM levels, with comprising over 50% of total PM mass due to diffusion-flame . For a typical gasoline-fueled passenger vehicle with a four-stroke engine, tailpipe CO₂ emissions average about 400 grams per mile, reflecting the carbon content of gasoline (approximately 87% by weight) oxidized during operation. With three-way catalytic converters standard since the 1980s, compliant modern engines limit CO to under 1 gram per mile, NMOG to 0.03–0.3 grams per mile (fleet averages), and NOx to 0.03 grams per mile under federal test procedures. Diesel four-stroke engines, prevalent in heavy-duty applications, exhibit higher NOx (up to 9–10 g/kWh without selective catalytic reduction) and PM (dominated by soot, reduced 99% from 1996 baselines via diesel particulate filters under Tier 4 standards implemented by 2015). Emission profiles vary with load and technology; for instance, rich-burn conditions elevate CO and HC, while diesel operation favors and formation due to higher temperatures and localized fuel-rich zones. Post-combustion controls like and aftertreatment systems have empirically reduced total pollutants by 70–99% in regulated fleets since the , though raw exhaust without mitigation shows +HC factors of 3.7–9.2 g/MJ in marine diesel examples.

Regulatory responses and technological counters

In response to rising concerns over air pollution from internal combustion engines, regulatory bodies implemented stringent emission standards targeting hydrocarbons (HC), carbon monoxide (CO), nitrogen oxides (NOx), and particulate matter (PM). In the United States, the Environmental Protection Agency (EPA), under the Clean Air Act Amendments of 1970, established initial federal standards for new light-duty vehicles effective from model year 1975, limiting CO to 15 g/mi, HC to 1.5 g/mi, and NOx to 3.1 g/mi, with progressive tightening through subsequent tiers such as Tier 2 (phased in 2004-2007) reducing NOx to 0.07 g/mi and non-methane organic gases to 0.075 g/mi. In the European Union, Euro 1 standards took effect for new passenger cars in 1992, followed by Euro 6 implementation from September 2014, which capped NOx at 60 mg/km for diesel and 80 mg/km for gasoline engines while introducing particle number limits of 6 × 10^11 per km for direct-injection gasoline engines. These regulations spurred adoption of exhaust aftertreatment systems, notably three-way catalytic converters (TWCs), mandated in the from 1981 for closed-loop control to enable simultaneous reduction of CO (up to 99% conversion), HC (up to 98%), and (up to 90%) under stoichiometric air- ratios near 14.7:1. (EGR) emerged as an in-cylinder control measure, diluting intake charge with 5-15% recirculated exhaust to lower combustion temperatures below 2,200 K and suppress formation rates, achieving 30-50% reductions in gasoline spark-ignition engines when combined with TWCs. (GDI), commercialized widely from the late 1990s, enabled stratified operation for improved and reduced CO/HC emissions by precise metering, though it increased PM necessitating downstream particulate filters (GPFs) compliant with 6 limits. Discrepancies between laboratory type-approval tests and real-world emissions, where NOx from diesel vehicles averaged 4.5 times lab limits under varied driving conditions, prompted regulatory refinements including the EU's Real Driving Emissions (RDE) protocol from 2017, enforcing on-road conformity factors up to 2.1 for NOx and requiring portable emissions measurement systems. Technological counters evolved accordingly, with advanced TWCs incorporating palladium-rhodium formulations for faster light-off (under 50 seconds to 50% efficiency) and EGR coolers to mitigate intake heating penalties, yielding overall fleet reductions of over 99% in CO and HC since 1970 baselines per EPA assessments. For PM from GDI engines, coated GPFs trap 80-90% of particles while minimizing backpressure, integrated into systems achieving Euro 6d compliance by 2021.

Recent Developments

Efficiency and material advancements

Advancements in four-stroke engine efficiency have focused on optimizing thermodynamic cycles and combustion processes to approach theoretical limits. The , which employs early intake valve closure to achieve a higher than , has enabled gains in turbocharged spark-ignition engines by reducing pumping losses and mitigating knock, with experimental implementations showing brake specific fuel consumption improvements of up to 9% at 2000 rpm. In diesel applications, achieved a record brake of 53.09% in a four-stroke engine unveiled in 2024, surpassing prior benchmarks through advanced and turbocharging refinements. Gasoline engines have similarly progressed, with Toyota's M-series engines reaching approximately 40% via high and introduced in models from 2018 onward, while Delphi's gasoline direct-injection compression-ignition prototype demonstrated 43.5% efficiency in 2022 testing. Material innovations have supported these efficiency gains by enabling higher operating temperatures and reduced frictional losses. Ceramic thermal barrier coatings on pistons, typically 0.5 mm thick, have increased thermal efficiency by 7-10% in diesel engines by minimizing heat transfer to coolant, as evidenced in controlled tests where coated pistons raised peak efficiency at low speeds like 1000 rpm. Lightweight alloys, including advanced aluminum and magnesium composites for cylinder blocks and heads, have reduced engine mass by 10-20% in recent designs, improving overall vehicle efficiency without compromising durability. Enhanced cast iron alloys with improved thermal conductivity have further allowed sustained high-performance operation in turbocharged four-stroke engines deployed since 2020. Friction-reducing surface treatments, such as diamond-like carbon coatings on piston rings, contribute additional 2-5% efficiency uplifts by lowering mechanical losses, particularly in downsized engines prevalent in 2020-2025 automotive applications.

Alternative fuel integrations

Four-stroke engines, primarily spark-ignition (SI) and compression-ignition (CI) variants, have been modified to integrate s such as , (CNG), , and biofuels, enabling operation alongside or in place of conventional or diesel while addressing and emissions goals. These adaptations typically involve fuel system redesigns, including specialized injectors, vaporizers, or dual-fuel setups, alongside adjustments to compression ratios, , and materials for resistance. For instance, flex-fuel engines in SI four-stroke configurations use sensors to detect ethanol content and adjust fueling dynamically, supporting blends from E0 to (85% ). Such systems leverage ethanol's higher (around 108 for E85 versus 95 for ), permitting advanced spark timing for potential efficiency gains of up to 5-10% in knock-limited conditions, though lower (about 30% less than gasoline) increases volumetric fuel consumption by 20-30%. CNG integration in four-stroke SI engines often employs port injection or direct injection with high-pressure storage cylinders (200-250 bar), yielding lower particulate matter and emissions compared to equivalents due to methane's cleaner . Performance studies indicate (BSFC) can be 12-20% lower than across operating speeds, attributed to optimized air-fuel ratios and reduced throttling losses, though dedicated CNG designs may sacrifice some low-end without turbocharging. In dual-fuel modes, CNG substitutes up to 90% of diesel in CI four-stroke engines via low-pressure , maintaining power output while cutting CO2 by 20-25% on a well-to-wheel basis, as demonstrated in marine applications. Hydrogen-fueled four-stroke SI engines utilize direct injection during the compression stroke to mitigate backfire and pre-ignition risks inherent to hydrogen's wide flammability limits (4-75% in air) and high flame speeds (up to 2.7 m/s versus 0.4 m/s for ). These adaptations achieve thermal efficiencies exceeding 40% in prototypes, surpassing counterparts by 10-15% through operation and reduced heat losses, with zero tailpipe CO2 but elevated from higher combustion temperatures requiring . Yanmar's 2024 development of a hydrogen four-stroke engine for coastal power generation highlights ongoing commercialization, targeting 50-100 kW outputs with cryogenic or compressed storage integrations. Biofuel compatibility in four-stroke engines varies by type: (fatty acid methyl esters) blends up to B20 (20% ) in CI engines require minimal hardware changes beyond seal material upgrades to counter oxidation and issues, preserving over 5,000-10,000 hours with proper . SI four-stroke engines handle ethanol-derived s seamlessly in flex-fuel setups, while marine four-stroke designs from manufacturers like MAN Energy Solutions accommodate straight vegetable oils or hydrotreated vegetable oils without efficiency penalties beyond initial blending. , gaining traction in four-stroke marine engines, employs corrosion-resistant components and dual-fuel pilots, reducing lifecycle carbon footprints by up to 95% with green production, though storage challenges persist due to its hygroscopic nature. Overall, these integrations demand empirical validation of long-term wear, as alternative fuels can accelerate deposits or dilution without tailored .

References

  1. https://www.energy.gov/eere/vehicles/articles/internal-combustion-engine-basics
  2. https://www1.grc.nasa.gov/beginners-guide-to-aeronautics/internal-combustion-engine-otto-cycle/
  3. https://eaglepubs.erau.edu/introductiontoaerospaceflightvehicles/chapter/reciprocating-engine-propeller/
  4. https://accelleron.com/charge-magazine/how-nikolaus-august-otto-created-the-4-stroke-internal-combustion-engine
  5. https://www.invent.org/inductees/nicolaus-august-otto
  6. https://www.gracesguide.co.uk/Alphonse_Beau_de_Rochas
  7. https://www.leadingedgeonly.com/article/the-four-stroke-cycle
  8. https://stories.technik-museum.de/en/four-stroke-engine
  9. https://www.eia.gov/kids/history-of-energy/famous-people/otto.php
  10. https://www.thoughtco.com/nicolaus-otto-engine-design-4072867
  11. https://web.mit.edu/16.unified/www/FALL/thermodynamics/notes/node26.html
  12. https://www.purdue.edu/freeform/me200/wp-content/uploads/sites/29/2023/04/ME-200-Chapter-9.pdf
  13. https://dieselship.com/marine-technical-articles/motor-engineering-knowledge/a-comparison-study-of-otto-diesel-cycles-and-suitability-of-natural-gas/
  14. http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/diesel.html
  15. https://nap.nationalacademies.org/read/21744/chapter/16
  16. https://www.sciencedirect.com/science/article/abs/pii/S019689040600344X
  17. https://www.deutz.com/en/company/our-history/milestones/
  18. https://www.thoughtco.com/who-invented-the-car-4059932
  19. https://group.mercedes-benz.com/company/tradition/company-history/1885-1886.html
  20. https://www.gasenginemagazine.com/gas-engines/first-overhead-cam-engine-zmtz19jjzhur/
  21. https://mydigitalpublication.com/article/Overhead%2Bvalve%2Bengine/3206769/472945/article.html
  22. https://macsmotorcitygarage.com/henry-fords-first-4-cylinder-production-ca-the-1904-06-model-b/
  23. https://www.grc.nasa.gov/www/k-12/airplane/engopt.html
  24. https://www.grc.nasa.gov/www/k-12/airplane/ottoa.html
  25. https://dieselnet.com/tech/engine_efficiency.php
  26. https://www.enginelabs.com/?p=282495
  27. https://www.caranddriver.com/news/a15345875/what-is-the-atkinson-combustion-cycle-and-what-are-its-benefits/
  28. https://dieselnet.com/tech/engine_miller-cycle.php
  29. https://www.sciencedirect.com/science/article/abs/pii/S0196890405000622
  30. https://energyeducation.ca/encyclopedia/Four_stroke_engine
  31. https://www.energy.gov/sites/prod/files/2014/03/f8/deer11_edwards.pdf
  32. https://sites.lafayette.edu/egrs352-sp14-cars/energy-losses/
  33. https://www.mdpi.com/1996-1073/14/20/6656
  34. https://www1.grc.nasa.gov/beginners-guide-to-aeronautics/engine-thermodynamic-analysis/
  35. https://www.sciencedirect.com/science/article/pii/S2666691X20300063
  36. https://www.nap.edu/read/12924/chapter/6
  37. https://cefrc.princeton.edu/sites/g/files/toruqf1071/files/reitz_princeton-day1-hour3-2018.pdf
  38. https://fiveable.me/thermodynamics-ii/unit-14/four-stroke-two-stroke-engine-cycles/study-guide/7mUupC7ap1Zi5vFS
  39. https://fiveable.me/thermodynamics-ii/unit-14/engine-performance-parameters-efficiency/study-guide/MkznQsGGCpx5wVt0
  40. https://achatespower.com/stroke-to-bore/
  41. https://blog.amsoil.com/how-does-an-engine-work-combustion-components/
  42. https://www.theengineeringchoice.com/what-is-four-stroke-engine/
  43. https://dsportmag.com/the-tech/valvetrain-how-it-works/
  44. https://primesourceco.com/latest-news/what-are-the-different-parts-of-a-4-stroke-engine/
  45. https://www.enginebuildermag.com/2015/04/timing-components/
  46. https://www.gpp-india.com/blog/valvetrain-component-purpose-types-and-their-functionality
  47. https://www.jdpower.com/cars/shopping-guides/what-do-dohc-sohc-and-ohv-stand-for
  48. https://mechanics.stackexchange.com/questions/6327/ohv-vs-ohc-which-is-faster-in-speed-horse-power
  49. https://www.caranddriver.com/news/a15341425/variable-valve-timing-explained-an-appreciation-of-how-quickly-engines-operate/
  50. https://dieselnet.com/tech/air_vva.php
  51. https://x-engineer.org/turbocharging/
  52. https://accelleron.com/charge-magazine/the-fundamentals-of-turbocharging
  53. https://accelleron.com/charge-magazine/how-forced-induction-improved-internal-combustion-engines
  54. https://www.mdpi.com/1996-1073/15/8/2721
  55. https://www.sciencedirect.com/science/article/abs/pii/S0196890419303711
  56. https://onlinelibrary.wiley.com/doi/10.1155/2021/6673612
  57. https://www.sciencedirect.com/science/article/abs/pii/S0196890418308021
  58. https://www.sciencedirect.com/science/article/abs/pii/S0306261917310413
  59. https://www.enginebuildermag.com/2016/08/understanding-rod-ratios/
  60. https://www.enginebuildermag.com/2023/03/does-connecting-rod-length-matter/
  61. https://www.k1technologies.com/k1-blog/stroker-science-piston-speed-rod-angle-and-increased-displacement-explained/
  62. https://www.irjet.net/archives/V7/i5/IRJET-V7I5670.pdf
  63. https://www.sciencedirect.com/topics/engineering/engine-durability
  64. https://journals.pen2print.org/index.php/ijr/article/download/19404/19053
  65. https://www.uti.edu/blog/diesel/gas-vs-diesel-engines
  66. https://www.valvolineglobal.com/en-ksa/difference-between-diesel-and-petrol-engines/
  67. https://www.quora.com/How-does-4-stroke-diesel-engine-cycle-operation-different-from-a-4-stroke-gasoline
  68. https://engines.honda.com/support-and-service/fuel-recommendations
  69. https://extension.okstate.edu/fact-sheets/ethanol-gasoline-blends-and-small-engines.html
  70. https://www.husqvarna.com/au/learn-and-discover/what-type-of-fuel-does-a-lawn-mower-use-choosing-the-right-fuel-for-your-mower/
  71. https://www.energy.gov/eere/vehicles/national-laboratory-reports-relating-intermediate-ethanol-blends
  72. https://www.rivieramm.com/news-content-hub/news-content-hub/methanol-leads-the-pack-on-four-stroke-fuel-alternatives-72719
  73. https://www.sae.org/papers/behavior-a-small-four-stroke-engine-using-fuel-methanol-gasoline-mixtures-2003-32-0024
  74. https://www.intechopen.com/chapters/66638
  75. https://www.everllence.com/our-focus/future-technologies/future-fuels-engines
  76. https://www.uti.edu/blog/automotive/ignition-timing
  77. https://www.sae.org/papers/a-three-dimensional-study-flame-propagation-a-spark-ignition-engine-630487
  78. https://www.jstage.jst.go.jp/article/jsme1958/4/15/4_15_583/_article/-char/en
  79. https://www.researchgate.net/publication/356391373_Emission_formation_in_IC_engines
  80. https://pubs.acs.org/doi/10.1021/acsomega.2c02907
  81. https://nepis.epa.gov/Exe/ZyPURL.cgi?Dockey=9100S4W0.TXT
  82. https://www.osti.gov/servlets/purl/1394423
  83. https://dieselnet.com/tech/diesel_emiform.php
  84. https://theicct.org/stack/vehicle-nox-emissions-the-basics/
  85. https://www.mdpi.com/1996-1073/18/3/454
  86. https://dieselnet.com/tech/engine_egr_emissions.php
  87. https://www.sciencedirect.com/science/article/abs/pii/S2213343716301452
  88. https://aiche.onlinelibrary.wiley.com/doi/10.1002/ep.70012
  89. https://www.cycleworld.com/blogs/ask-kevin/four-stroke-engine-history-explained/
  90. https://www.futuremarketinsights.com/reports/passenger-vehicles-market
  91. https://bostechauto.com/blog/introduction-to-the-types-of-diesel-truck-engines/
  92. https://www.quora.com/Are-diesel-truck-engines-four-stroke-engines
  93. https://www.cummins.com/news/2023/05/23/what-diesel-engine-and-what-are-types-and-components-diesel-engine
  94. https://mechanics.stackexchange.com/questions/23865/why-do-heavy-vehicles-almost-always-use-diesel-engines
  95. https://global.yamaha-motor.com/stories/offroadmania/ch5/
  96. https://www.accio.com/business/trending-2024-motorcycles-4-stroke
  97. https://primesourceco.com/latest-news/the-difference-between-a-2-stroke-and-4-stroke-engine/
  98. https://www.epa.gov/sites/default/files/2015-07/documents/catalog_of_chp_technologies_section_2._technology_characterization_-_reciprocating_internal_combustion_engines.pdf
  99. https://www.cat.com/en_US/products/new/power-systems/industrial/industrial-diesel-engines/18375224.html
  100. https://www.epa.gov/stationary-engines/fact-sheet-final-air-toxics-standards
  101. https://www.cat.com/en_US/products/new/power-systems/industrial/industrial-diesel-engines/15969713.html
  102. https://www.man.eu/engines/en/products/marine/engines-for-commercial-shipping/commercial-shipping.html
  103. https://nautilusshipping.com/news-and-insights/15-accurate-differences-between-two-stroke-and-four-stroke-marine-engines
  104. https://www.wartsila.com/marine/products/engines-and-generating-sets/dual-fuel-engines/wartsila-31
  105. https://www.everllence.com/marine/products/four-stroke-engines/propulsion
  106. https://www.dieselduck.info/machine/01%2520prime%2520movers/diesel_engine/diesel_engine.02.htm
  107. https://hpwizard.com/bmep.html
  108. https://www.topspeed.com/most-powerful-four-cylinder-engines-ever-built/
  109. https://www.sciencedirect.com/science/article/pii/S0360128520300861
  110. https://saemobilus.sae.org/articles/thermal-efficiency-enhancement-a-gasoline-engine-2015-01-1263
  111. https://www.researchgate.net/publication/275258615_Thermal_Efficiency_Enhancement_of_a_Gasoline_Engine
  112. https://x-engineer.org/brake-specific-fuel-consumption-bsfc/
  113. https://mechanics.stackexchange.com/questions/25049/what-makes-two-stroke-engines-less-fuel-efficient-than-four-strokes
  114. https://www.uti.edu/blog/marine/2-stroke-vs-4-stroke
  115. https://pmc.ncbi.nlm.nih.gov/articles/PMC1247506/
  116. http://envirolink.govt.nz/assets/Envirolink/232-WCRC26.pdf
  117. https://www.researchgate.net/publication/350459522_Comparative_Studies_on_Control_of_Emissions_of_Two_Stroke_and_Four_Stroke_Spark_Ignition_Engines
  118. https://blog.amsoil.com/two-stroke-vs-four-stroke/
  119. https://inspenet.com/en/articulo/2-stroke-vs-4-stroke-engines-comparison/
  120. https://www.researchgate.net/publication/344860096_Comparison_of_the_Overall_Energy_Efficiency_for_Internal_Combustion_Engine_Vehicles_and_Electric_Vehicles
  121. https://www.performanceracing.com/magazine/columns/10-01-2021/make-case-ice-vs-electric-motors
  122. https://www.alphamotorinc.com/about/ev-vs-ice-transmission-technology-explained
  123. https://www.researchgate.net/figure/Theoretical-energy-density-of-different-batteries-and-gasoline_tbl1_358111375
  124. https://theicct.org/publication/a-global-comparison-of-the-life-cycle-greenhouse-gas-emissions-of-combustion-engine-and-electric-passenger-cars/
  125. https://www.mdpi.com/2032-6653/16/5/287
  126. https://www.rizontruck.com/blogarticle/ev-maintenance-vs-gas-and-diesel-understanding-the-differences/
  127. https://insideevs.com/news/721836/ev-repair-costs-vs-ice-q1-2024/
  128. https://tcg.engineer/striking-the-balance-where-function-meets-the-future-means-closely-examining-fueling-versus-electric-charging-stations/
  129. https://www.chargedfuture.com/ev-charging-vs-gas-refueling/
  130. https://pmc.ncbi.nlm.nih.gov/articles/PMC7108289/
  131. https://www.epa.gov/system/files/documents/2024-10/c03s02_2024-update_0.pdf
  132. https://dieselnet.com/tech/dpm.php
  133. https://www.epa.gov/system/files/documents/2023-01/new-motor-veh-air-poll-control-hd-eng-veh-stnd-frm-2022-12-20.pdf
  134. https://www.ncbi.nlm.nih.gov/books/NBK294260/
  135. https://link.springer.com/article/10.1007/s10098-014-0793-9
  136. https://www.epa.gov/greenvehicles/greenhouse-gas-emissions-typical-passenger-vehicle
  137. https://www.ecfr.gov/current/title-40/chapter-I/subchapter-C/part-86/subpart-S/section-86.1811-27
  138. https://www.ijmerr.com/uploadfile/2015/0409/20150409042911754.pdf
  139. https://www.crossco.com/resources/articles/what-are-tier-4-diesel-engine-standards/
  140. https://www.sciencedirect.com/science/article/abs/pii/S0378382007002160
  141. https://dieselnet.com/tech/engine_emission-control.php
  142. https://www.mdpi.com/2077-1312/11/2/413
  143. https://www.epa.gov/emission-standards-reference-guide/basic-information-about-emission-standards-reference-guide-road
  144. https://pmc.ncbi.nlm.nih.gov/articles/PMC9098155/
  145. https://www.meca.org/wp-content/uploads/resources/MECA_stationary_IC_engine_report_0515_final.pdf
  146. https://pubs.acs.org/doi/10.1021/acsomega.3c09052
  147. https://www.researchgate.net/publication/344395819_Emission_Reduction_in_Four-Stroke_SI_Engine_Using_EGR_and_Catalytic_Converter
  148. https://theicct.org/wp-content/uploads/2021/06/ICCT_RoadTested_201709.pdf
  149. https://www.epa.gov/sites/default/files/2020-07/documents/ic-engines_ria_final-rice-engines_2004-02.pdf
  150. https://www.sae.org/publications/technical-papers/content/13-02-02-0007/
  151. https://eureka.patsnap.com/blog/what-is-atkinson-cycle-engine/
  152. https://tanktransport.com/2024/04/diesel-engine-thermal-efficiency/
  153. https://www.mobilityengineeringtech.com/component/content/article/44117-sae-ma-03433
  154. https://iopscience.iop.org/article/10.1088/1757-899X/417/1/012021/pdf
  155. https://www.sae.org/papers/effects-ceramic-coatings-diesel-engine-performance-exhaust-emissions-910460
  156. https://www.automotive-technology.com/articles/new-trends-in-engine-and-engine-component-design
  157. https://australiansciencejournals.com/ajmet/article/download/2077/2175
  158. https://www.sciencedirect.com/science/article/pii/S2590174525000960
  159. https://afdc.energy.gov/vehicles/how-do-flexible-fuel-cars-work
  160. https://info.ornl.gov/sites/publications/files/pub54888.pdf
  161. https://journals.sagepub.com/doi/10.1177/1468087419833257
  162. https://www.researchgate.net/publication/289830922_Performance_analysis_of_a_4-stroke_SI_engine_using_CNG_as_an_alternative_fuel
  163. https://www.sciencedirect.com/science/article/abs/pii/S1364032115006255
  164. https://www.sciencedirect.com/science/article/pii/S2666352X25000755
  165. https://www1.eere.energy.gov/hydrogenandfuelcells/tech_validation/pdfs/fcm03r0.pdf
  166. https://pubs.acs.org/doi/10.1021/acsomega.3c05397
  167. https://www.yanmar.com/global/about/ygc/news/2024/01/09/128584.html
  168. https://extension.psu.edu/using-biodiesel-fuel-in-your-engine/
  169. https://www.sciencedirect.com/science/article/abs/pii/S0196890416307464
  170. https://www.man-es.com/marine/strategic-expertise/future-fuels/biofuel
  171. https://dieselnet.com/tech/fuel_biodiesel_comp.php
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