After graduation, Diesel returned to Paris and joined Linde's refrigeration company, managed by his former professor, Carl von Linde. He initially worked as a designer and project manager, gaining experience in practical engineering and business operations. This also allowed him to stay in the city where he was born and raised for a significant part of his childhood.

Diesel's exceptional performance led to his appointment as the director of Linde's manufacturing plant in Paris. This leadership role further honed his management skills and provided him with greater autonomy in engineering projects.

Diesel moved to Berlin to manage Linde's research and development activities. This move allowed him to focus on his own inventions and research interests more fully, including the development of a new type of engine.

Diesel patented his theoretical design for a new type of heat engine. This patent outlined the fundamental principles of the Diesel engine, including high compression ratios and the direct injection of fuel. This was a pivotal moment, marking the beginning of his engine's development.

Diesel collaborated with Maschinenfabrik Augsburg-Nürnberg (MAN) and Krupp to build and refine his engine design. This collaboration was crucial for the practical development of the engine, as these companies provided the resources and expertise necessary to overcome the considerable engineering challenges.

After years of intensive development and experimentation, the first functional Diesel engine was successfully tested in Augsburg. This marked a major breakthrough in engine technology and validated Diesel's theoretical concepts.