The compression ratio is the ratio of the volume of the cylinder measured before the piston is compressed to the volume after its fully compression. A compression ratio can create impact on the mechanical energy and fuel consumption of the engine. Let’s discuss the engine compression ratio in more detail and find out how it affects your car’s performance and efficiency.
What is Compression Ratio?
In combustion engines, fuel is ignited in a closed cylinder with a piston attached at one end. Compression ratio is basically the ratio of volume of the cylinder when the piston is fully compressed or relaxed. To measure compression ratio, before piston compression volume is divided by after compression volume. If the compression ratio value is five, it means that a mixture of air and fuel is compressed to one-fifth of its original length. The ratio value is dependent upon the cylinder capacity. However, a cylinder should never be used at its fullest, as it can cause engine knocking.
Working Principle
The compression ratio in diesel and petrol engines works more or less similar. The only difference that can impact it is the viscosity of fuel.
Petrol engines have a lower compression ratio in comparison to diesel engines. Air and fuel are mixed in a ratio of 10:1 to 14:1 inside the combustion chamber of the engine. A spark is used as a source of ignition that burns homogenous mixture instantly and completely. Other technologies like: indirect injection, direct injection, common-rail direct injection and compression ignition can also be used for sparking.
Static vs Dynamic Compression Ratio
The compression ratio of engines are of two types: status and dynamic. Static compression ratio (SCR) is a volume of the cylinder when the piston is at full crank. Whereas, dynamic compression ratio (DCR) is a volume of the cylinder measured when the piston is at its lowest crank.
The major difference between status and dynamic compression ratio is substantial. Static compression ratio is calculated by dividing cylinder volume and intake of fuel. Whereas, dynamic compression ratio is obtained by calculating dimensions of an engine. Moreover, SCR is capable of changing its values during combustion which dynamic ratio can not. Therefore, the value of SCR is always higher than DCR.
Higher Compression Ratio and Engine
The compression ratio creates a direct and significant impact on combustion engines. The first impact is on the thermodynamic cycle as the compression ratio is responsible for increasing temperature and pressure inside the cylinder.
Furthermore, increased pressure and temperature will cause a fire inside the chamber to reach the piston more rapidly without letting heat escape. Therefore, a higher compression ratio is capable of creating more horsepower by using a lesser amount of fuel. It also burns all the fuel trapped in the periphery combustion chamber increasing fuel efficiency even more.
Latest Development in Compression Ratio
The latest development in compression ratio used is in the form of variable compression ratio engines. Older petrol and diesel engines can work on the optimum compression ratio that they are designed for. However, the variable compression ratio engine can change its compression ratio while driving. The first variable engine was introduced in the year 2019.
This was all about the engine compression ratio. If you are interested in driving a car with a variable compression ratio engine, browse through these used cars for sale in the UAE.
Stay tuned to UAE’s top auto blog for more information on compression ratio.
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