spontaneously, generating the downward power stroke of the piston.- A gasoline engine compresses air and fuel at a ratio of 8:1 to 12:1 (on
average), while a diesel engine compresses at a ratio of 14:1 to as high as
25:1. The higher the compression ratio of the diesel engine, the better the
combustion efficiency. Why? Because as the combustion ratio increases, the
temperature increases, and the diesel fuel is burned more completely and
efficiently. - Gasoline engines generally use either carburetion (in which the air and fuel is
mixed long before the mixture enters the engine cylinder), or fuel injection (in
which case the fuel is injected at the intake stroke, outside of the cylinder). In
contrast, diesel engines use direct fuel injection. The diesel fuel is injected
directly into the engine’s cylinder when the piston is at the top of the
compression stroke (TDC).
Diesel Fuel vs. Gasoline
Those of you who have compared diesel fuel and gasoline know that they are
quite different. They smell differently, and diesel fuel is heavier and oilier.
Diesel fuel has a higher energy density than gasoline. A quick chemistry lesson
illustrates this fact:
- 1 gallon (3.8 liters) of diesel fuel contains approximately 155 × 106 joules or
147,000 btu of energy. - 1 gallon of gasoline contains 132 × 106 joules or 125,000 btu of energy.
In short, you get more bang for your buck out of a gallon of diesel fuel than
you do from a gallon of gasoline.