Diesel is not car fuel and oil mixed together, it's not a type of "gas," it is a lower-grade petroleum distillate used in DIESEL ENGINES which has a much higher flashpoint and whose fumes are non-explosive as opposed to gasoline's. Diesel engines use "compression-ignition" (the heat of highly compressed air in the combustion chamber) to ignite a very fine mist of diesel fuel. Used in heavy-duty trucks, generators, pumps, etc. for their higher specific torque (vs. gasoline) and greater fuel efficiency. Modern diesels are very clean, efficient, smooth, and quieter.
My Ford/Chevy/Dodge truck has a diesel engine which runs on diesel fuel. Neato!