Both diesel and gasoline engines have been used in automobiles since the late nineteenth century. Today, gasoline engines are used to power most passenger cars and trucks whereas diesel engines are used mainly in large commercial vehicles and heavy duty trucks. This is because diesel engines provide an immense amount of power from a dead stop, which is a necessity when moving a heavy load. However, most diesel engines yield poor acceleration characteristics, which makes them less fitted for use in the average passenger car.  Most people can pick out a diesel engine a mile away because of it’s loud and aggressive growl compared to a gasoline engine. The principles of how both engines work are almost exactly the same, but the actual engine operation is quite different.

Diesel and gasoline engines operate almost exactly the same way. Both engines utilize the four stroke cycle through the use of valves, pistons, and a crankshaft. What makes these engines so different from one another is that conventional gasoline engines use a spark ignition system while diesel engines run using compression ignition. Spark ignition uses an electrical spark from a spark plug to ignite the compressed air/fuel mixture in the combustion chamber. Compression ignition engines (diesel engines) simply use the heat created by compression to ignite the air/fuel mixture rather than a spark. The ignition is typically triggered by the injection of fuel into the combustion chamber. The fuel systems on diesel powered vehicles are much more complex than on a gasoline vehicle because diesel fuel systems often need to hold thousands of pounds of fuel pressure to operate properly. Diesel engines also have much higher compression ratios than gasoline engines, which is why they are able to produce a huge amount of power from a stop.

The differences between spark ignition and compression ignition leads to another difference in they way diesel and gasoline engines operate. A regular spark ignition gasoline engine controls it’s speed and power output by a throttle valve. The throttle valve is operated by the driver through the accelerator pedal, and controls the amount of air that is allowed to enter the engine. The engine computer uses sensors to send more fuel to the engine to compensate for the larger amount of air. On a diesel engine, the fuel system is responsible for regulating engine speed. As the driver depresses the accelerator pedal, more fuel is injected into the combustion chambers, resulting in an increase in engine speed.

Performance characteristics are also a major difference between diesel and gasoline engines. Diesel engines are designed to produce a large amount of power at relatively low engine speeds, which makes them ideal for towing and hauling. Gasoline engines provide steady acceleration through a wide power band, which makes them perfect for the everyday passenger car. Diesel engines have been used in passenger cars as well because of their high fuel economy ratings. However, diesels are louder, rougher, and have a much smaller power band when compared to a gasoline engine.