Rudolf Diesel invented his world-changing engine in the 1890s. What shocking fuel did he originally design it to run on?

Peanut oil could power Diesel’s engine

Rudolf Diesel’s engine was not tied to the petroleum fuel now associated with its name. At the 1900 Paris Exposition, an engine of his design was demonstrated running on peanut oil. The striking point was not that every diesel engine was meant to burn peanuts, but that the design could work with a plant-based oil.

Compression lets the fuel ignite

A diesel engine first squeezes air inside its cylinder until the air becomes very hot. It then sprays in fuel, which ignites from that heat—no spark plug required. That combustion method gave Diesel room to consider different fuels, provided they could be injected and burned effectively.

Peanut oil was therefore a practical demonstration of fuel flexibility, not a claim that it was the sole or ordinary fuel for the engine. Petroleum-based diesel eventually became the familiar choice, but Diesel’s experiment showed that the engine’s basic principle could also turn an agricultural product into working power.

A different idea of where fuel could come from

That possibility mattered especially where crops were easier to obtain than petroleum. In principle, a region could use oil from locally grown plants to run machinery. The memorable detail is that the engine’s name points to the inventor, not to an exclusive fuel: one of its early demonstrations ran on an oil pressed from peanuts.