Diesel engine
Both the Diesel engine, and the Akroyd engine run the same kind of fuel, petroleum oil, which has led to a dispute about whether or not the Diesel engine is based upon the Akroyd engine. The fact that the Diesel engine's operating principle differs from the operating principle Rudolf Diesel describes in his essay "Theory and Construction of a Rational Heat Motor" further contributed to this. The Akroyd engine was the first functional internal combustion engine that could use petroleum oil as fuel. It was operational in 1891, six years before the Diesel engine first ran. However, after the Diesel engine had proven successful, "Diesel engine" became the synonym for an engine that ran on any sort of petroleum oil. "Oil engines" that used the Akroyd operating principle were called "Semi-Diesel", and the name "Akroyd", which had been associated with oil engines, fell out of use. Therefore, Herbert Akroyd Stuart sought to replace the term Diesel engine with Akroyd engine in the early 20th century.