On heat engines
Almost every time people find out that I have a diesel-powered car, they will ask why I would want—why I would pay more—for such a thing. I usually start by describing the fuel mileage I get, and how I like the extra torque at low RPM it affords me; this explanation satisfies most inquisitors. Even more, however, diesel engines appeal to my aesthetic sense: I like things that are elegant.
In a gasoline engine, fuel and air are mixed before they are injected into the cylinder, compressed, and ignited by the spark plug. A diesel engine compresses only air; when the piston reaches its highest point, fuel is injected and spontaneously combusts because compression has raised the temperature of the air above the flash point of the fuel. Put another way, a gasoline engine uses the physical relationship of temperature and pressure in a gas in one direction: to push the piston down after ignition. A diesel engine uses that relationship twice: once to heat the air enough to ignite the fuel, and again to push the piston down, producing power.
So I hope the dealer finishes fixing my car today; the one they lent me is nice, but the sound of it starting just doesn’t bring me the same thermodynamically-inspired smile.
