2 STROKE VS. 4 STROKE Engines
A simple explanation by Jonas Borchert
The 2-stroke engine has a Bore (diameter of cylinder) measure of 66.4mm and a stroke length of 72.0mm giving it the combustion chamber fuel capacity of Bore x Stroke= 66.4mm x 72.0mm = 478.1 cm3 In the engine specisications we also find that the compression ratio varies between 8.9~10.6 : 1, which means that the volume of air in the cylinder (when the piston is at its lowest point) is 8.9~10.6 times greater than the volume when the piston is at its highest point (In the compression stroke). We notice that the 2-stroke engine uses ports at the side of the cylinder instead of valves that are placed at the top of the combustion chamber. This indicated less material needed to build the 2-stroke engine, it is lighter and is able to have a larger combustion chamber fuel capacity as there is now more space in the combustion chamber.
Bore x Stroke= 77.0mm x 53.6mm= 412.7cm3 where the 4-stroke engine has a Bore measure of 77.0mm and a Stroke length of 53.6mm. Due to the smaller combustion chamber fuel capacity the 4-stroke engine has been fitted with a compression ratio of 13.5 : 1, leading to a greater volume and density of air than the 2-stroke engine when the piston is at its highest point. The compression ratio for the 2-stroke varies between 8.9~10.6 : 1, which means that the volume of air in the cylinder (when the piston is at its lowest point) is 8.9~10.6 times greater than the volume when the piston is at its highest point.
The 2 stroke
4 stroke engine fuel capacity
Now that we have the engine specifications for Bore Measure, Stroke length and Compression Ratio- we can solve for the Swept Volume and Clearance Volume through the formula above. This formula is used to calculate the compression ratio in internal and external combustion engines:
Cr=(Vs+Vc)÷Vc
Cr = Compression RatioVs = Swept Volume (calculated by using the formula:
Vs (swept volume) = π x r2 x stroke, where r is the radius of the cylinder).
Swept volume or cc = Cubic centimeters measured from the area between when the piston is at the very botom and very top of its travel inside the cylinders, multiplied by the amount of cyclinders.
Vc= Clearance Volume when the piston is at TDC (minimum volume of space at the end of the compression stroke).
Note: TDC = Top Dead Center (top of stroke)BDC= Bottom Dead Center (bottom of stroke)