. . is ignition. Diesel injector sprays fuel into air heated by compression. This allows diesels to use crude, less volatile fuel. Such fuel is cheaper and yields more energy per gallon.

On the negative side, the injection process causes a sort of explosion which causes diesel engines to be noisy, and the crude fuel results in high levels of air polution, in particular, particulate, some of which may be cancer causing. They also smell real bad. I refer to diesel Mercedes (of which there still are some around here) as "stench cars".

Diesel was popular for awhile with "Volvo liberals", ecofreaks and other self appointed "counter culture" types because they were sure there would still be diesel during gasoline shortages. Air polution and health problems just didn't come up - they were just as good at self serving denial as today's SUV drivers. Fortunately that generation of vehicles is all in the junk yards by now.

Herr Diesel himself was a victim of the diesel engine. He just couldn't understand why the government of Germany was supressing his efforts to market his invention, so he got on a channel ferry to go sell it in England. The passenger list was short one Kraut at the other side. The German government had already decided that the low volutility of diesel fuel made it ideal for uboats, and if Herr Diesel didn't have the sense to keep his mouth shut, they would help.