Diesel Engines vs. Gasoline Engines

Diesel engines and gasoline engines are quite similar. Both are internal combus­tion engines which convert the chemical energy of fuel into mechanical energy. Internal combustion engines covert fuel into energy through a series of small explosions or combustions. The major difference between diesel and gasoline is how these explosions occur. In a gasoline engine, fuel is mixed with air, compressed by pistons and ignited by sparks from spark plugs. In a diesel engine, the air is compressed first, and then the fuel is injected.

This series of explosions or combustions is called the injection process. Most car engines use port injection or a carburetor. A port injection system injects fuel just prior to the intake stroke (outside the cylinder). A carburetor mixes air and fuel long before the air enters the cylinder.


Diesel engines use direct fuel injection, where diesel fuel is injected directly into the cylinder. The injector on a diesel engine is its most complex component and must withstand the temperature and pressure inside the cylinder and still deliver the fuel in a fine mist. Getting the mist circulated in the cylinder so that it is evenly distributed is also a problem, so some diesel engines employ special induction valves, pre-combustion chambers or other devices to swirl the air in the combustion chamber or otherwise improve the ignition and combustion process.

Some diesel engines contain a glow plug. When a diesel engine is cold, the compression process may not raise the air to a high enough temperature to ignite the fuel. The glow plug is an electrically heated wire, similar to the hot wires seen in a toaster, that heats the combustion chambers and raises the air temperature when the engine is cold so that the engine can start. Smaller engines and engines that do not have such advanced computer control use glow plugs to solve the cold-starting problem.

Mechanics aren’t the only difference between diesel engines and gasoline engines. There’s also the issue of the fuel itself. The upcoming posts will give other differences between diesel and gasoline engines while continuing to illustrate how a diesel engine works. As always continue reading our blog learn more about diesel engines.

Steven Lynch


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