ENGINES {Week 3}

What is the purpose of a glow plug on a diesel engine?
The purpose of the glow plug on a diesel engine is to heat up the combustion chamber before the pistons start to move, this is because in a diesel engine, the air and fuel mixture ignites in high compression and heat. The glow plug is there to assist in starting up the cycles and later on turns off when the combustion chamber is hot enough.

What is the difference between a two stroke and four stroke petrol engine?


2 Stroke Engine: In a two stroke engine, while the piston travels down on the first stroke, the piston head unblocks the exhaust port. The inlet port is blocked and the transfer port is opened which lets the air, fuel and oil mixture from the bottom of the cylinder travel upwards and come out through the transfer port and into the combustion chamber.

With the centrifugal force, the piston travels upwards, this is the second stroke. In this stroke, while the piston is travelling upwards, it now opens the inlet port, further on it blocks the exhaust and transfer ports. The fuel mixture gets compressed and is ignited by the sparkplug at TDC. This process is repeated over and over again.

 In a two stroke engine, when the inlet port opens, air with fuel and oil is directed to the big end of the con rod and crankshaft which is lubricated by the mixture.

4 stroke engine:  In a four stroke engine, there are four cycles.

Stroke 1: When the piston is travelling down to BDC, the inlet valve is open to let in the air and fuel mixture. This is the inlet stroke.

Stroke 2: The piston is travelling upwards to TDC. In this stroke, both the inlet and the exhaust valves are closed, this stroke is called the compression stroke. The mixture of fuel and air is getting compressed and the area is getting much smaller.

Stroke 3: Once the piston is fully up to TDC, the mixture is ignited with a sparkplug at the top of the cylinder head. This ignition causes and explosion, the force drives the piston down to BDC. Both valves remain closed. This is the combustion stroke.

Stroke 4: The piston is being driven upward again by centrifugal force. In this stroke, only the exhaust valve opens and while the piston is travelling upwards to TDC, the burnt gases are driven out of the combustion chamber.