In regards to normal modern vehicles there are two main types of engines available, the two main types are either a petrol combustion engine or a diesel compression engine. To explain the differences we must first explain the similarities of both engine types. We will use a four cylinder engine as the basis as it is common in both petrol and diesel configurations.
In both diesel and petrol engines the following holds true. Both engine types convert burning fuel into mechanical energy through a common series of explosions inside the combustion chambers. These explosions force the rotation of the crank which in turn, by design, force another piston in the line up into the bore of the next cylinder in the firing order to repeat the process over and over again resulting in the rotation of the engine, this rotation of the engine is centered on the engines crankshaft which in turn is bolted to the gearbox, or transmission as it is sometimes called, this converts the power into energy used to move the vehicle.
Both engine types use a four stroke combustion cycle consisting of:
- An intake stroke in which the intake valves open and allow fresh air into the combustion chamber while the piston moves down in the cylinder.
- A compression stroke in which the piston travels back up the cylinder once the valves are closed compressing the air.
- A combustion stroke in which the newly compressed air mixed with fuel and then ignited creating a small explosion in the cylinder forcing the piston back down the cylinder bore.
- And an exhaust stroke where the exhaust valves open and the piston travels back up the cylinder bore to expel the exhaust from the last combustion.
The main difference between a petrol engine and a diesel engine is the way they perform the process of combustion. On the petrol engine the air and fuel are mixed at the intake stage and the fuel is atomised and ignited with the use of a spark plug while does what its name implies, creates a spark in the combustion chamber in order to ignite the fuel and air mixture. On a diesel engine there are no spark plugs, the ignition process is accomplished by the compression of the air itself, because of the higher compression of diesel engines by design the air when compressed reaches temperatures high enough to ignite when fuel is introduced into the cylinder at a specific time in the combustion cycle. This results in the the two different types of engines arriving at the same outcome, just simply arriving there by different means.
The basic design of the engines stays the same regardless of the manufacturer, the intake systems and fuel delivery systems do vary but at the end of that day the internal process is the same for all.
