RP-1 would work even better. A kerosene fuel developed in the 1950s as a more efficient alternative to alcohol-based rocket fuels, RP-1 powered the Soyuz and Falcon 9 spacecrafts. "It's a close relative of diesel fuel, so there is no real problem using it in diesel engines," Martinez-Sanchez says. "The only special thing about RP-1 is a lower volatility and a higher viscosity, so the engine might not run well on cold days," he says.