“(Diesel) originally designed the diesel engine to run on peanut oil. Only later did petroleum become the standard. In a 1912 speech, Diesel said ‘the use of vegetable oils for engine fuels may seem insignificant today, but such oils may become, in the course of time, as important as petroleum and the coal tar products of the present time.’”
Source: https://www.reliableplant.com/Read/23464/History-lesson-diesel-engine