Stroke
1A: Piston at BDC
In the diagram the piston is at BDC (Bottom Dead Centre - meaning it is at the lowest point of travel within the cylinder). The air, petrol and oil mixture within the crankcase is forced into the cylinder and exhaust gases are driven out.
In the diagram the piston is at BDC (Bottom Dead Centre - meaning it is at the lowest point of travel within the cylinder). The air, petrol and oil mixture within the crankcase is forced into the cylinder and exhaust gases are driven out.
Stroke
1B: The Instroke
The piston moves upwards and covers the air intake and exhaust ports closing them.
The piston moves upwards and covers the air intake and exhaust ports closing them.
The charge of fresh air is compressed to about 5:1 (20%) of its original volume. The act of compressing the air heats it tremendously.
This happens on every upward stroke of
the piston.
Stroke
2A: Piston at TDC
Just as the piston reaches the uppermost portion of it's travel at Top Dead Centre (TDC) the spark plug is fired causing combustion of the compressed mixture within the cylinder. At the same time petrol and oil vapour is being drawn into the crank-case in preparation for the next stroke.
Just as the piston reaches the uppermost portion of it's travel at Top Dead Centre (TDC) the spark plug is fired causing combustion of the compressed mixture within the cylinder. At the same time petrol and oil vapour is being drawn into the crank-case in preparation for the next stroke.
Stroke
2B: Piston nearing BDC
During the downward stroke the exhaust port opens, and the cylinder is
swept clean of burnt fuel by fresh air from the inlet port. The petrol,
oil and air charge within the crank-case is compressed during this stroke
in preparation for the next stroke.
This entire cycle is repeated for every revolution of the crank shaft.
