The concept of compression ratio, explained here, is one which is a prime factor in deciding the efficiency of any car engine. Compression is squeezing something, so that, it occupies a smaller volume. Ratio is the proportion between two quantities or numerical values. The basic unit of an assembly is a combustion chamber, piston combination. Compression ratio is a proportion which denotes the degree of compression achieved in an internal or external combustion engine, when the driving pistons compress the air-fuel mixture in every engine stroke. It is a ratio of air-fuel mixture volume when a piston is at the end of its up-stroke, to the air-fuel mixture volume at the end of its down stroke in a combustion chamber. It is a measure of air-fuel mixture compression and density achieved in every engine stroke. Let us see what are the various factors associated with a car engine compression ratio and see how it’s calculated.
Before one can understand what is a compression ratio in more details, one must first understand how a car engine works and what role do the combustion chamber and piston assembly play in it. The combustion chamber is a cylinder, which is fed with a mixture of air and vaporized combustion fuel. A piston is placed inside the combustion chamber and it makes up and down movements, according to pressure applied. The air-fuel mixture fed inside the combustion chamber is ignited, when you turn on the ignition of the car. The explosive combustion sets the piston moving up and every time it comes down, it compresses air-fuel mixture again, igniting it. The thrust provided by the combustion of fuel is transformed into the movement of car crankshaft, which ultimately drives the wheels! So, better the compression ratio, better is the density of air fuel mixture achieved during each compression and better is the efficiency of the engine in burning fuel.