THE DIESEL ENGINE
An understanding of a diesel engine and what sets it apart from gas fueled engines.
DIESEL VS GAS ENGINES
There are a few differences between diesel engines and petrol or (gas) fueled engines. A diesel engine is a type of internal combustion engine that uses compression to ignite the air fuel mixture rather than a spark plug. They can be found, mainly in heavy duty machinery and vehicles and are sought after because they generally require less mantanence and are more efficient than a high displacement gas engines. Diesel engines also have a higher compression ratio in order to ignite the air and fuel mixture. Most petrol engines will have a compression ratio of anywhere from 8:1 to 12:1 while a diesel engine will have a compression ratio of about 15:1 all the way up to 23:1.
DIESEL FOUR STROKE
Most diesel engines will use a four stroke cycle which is what you would find on most internal combustion engines. A four stroke cycle simply means there are four phases that must occur inside the cylinder in order to make power. The first stroke opens the intake valve while the piston is traveling down into the cylinder allowing fuel in. Once the piston comes backs up, it can compress the air and fuel that was let in as it travels back up the cylinder during the compression cycle. Once the piston reaches the top, most non-diesel engines will use a spark plug to ignite the fuel and air mixture creating an explosion and forcing the piston back down, this is considered the power stroke. The final phase is the exhaust stroke and during this phase the engine must get rid of the left over emissions created by the power stroke. This piston travels back up and pushes out the emissions with the exhaust valve open on the cylinder head. This process is repeated for how ever many cylinder the engine may have.
DIESEL TWO STROKE
Some older engine like Detroit Diesel used a two stroke design instead of four. A two stroke engine has the same phases as the four stroke engine, however it accomplishes this in two strokes instead of four. During the intake phase the piston is moving down in the cylinder, as it does this it uncovers the inlet port and allows fresh air into the cylinder, forcing the exhaust gases out as the exhaust valve opens, known as scavenging. As the piston travels back up it covers the inlet port thus cutting off more air from entering the cylinder. Just before the piston reaches the top, or top dead center, the injector releases fuel into cylinder. With most diesel engines there is no spark plug to ignite the mixture but instead is ignited by the heat of the compressed air. The expanding force from the explosion forces the piston back down allowing the inlet port back open and opening the exhaust valve again.