What is Engine Power?

The power developed by the engine mainly depend upon three factors:

1. The amount of air which can be passed throgh the combustion chamber per minute- Volumetric Efficiency

2. The completness with which air can be mixed with fuel and burnt- Thermal Efficiency

3.  How well the chemical energy of the burning fuel can be converted into mechanical work at the crankshaft- Mechanical Efficiency

Volumetric Efficiency:

It desribes how well the gas has passed the engine.It require minimum obstruction of gas flow both in and out.  Valve timing also plays an important role. Its also impotant to keep the fuel-air mixture temperature low at inlet as hot gas is more dense than cold one thus cylinder will carry a smaller mass of mixture.

Engines with higher volumetric efficiency will run at higher RPM and produce more overall power.There are few standard way to improve volumetric efficiency  like larger valve or multiple valve.

Thermal Efficiency:

The highest possible compression ratio which can be used without knocking (detonation) and the minimum loss of heat to the combustion walls are the two main requirements for thermal efficiency. For both reasons the combustion chamber needs to be as compact as possible as its surface area will be less thus leass heat loss also the compact chamber has less distance to travel hence mixture burns  quicker reducing knocking risk and due to proper burning less emission too.

Mechanical Efficiency:

The desigs of the mechanical parts of the engine all have a bearing on how well the result of the burning of the fuel equates to the turning of crankshaft. The loss of some efficiency due to the increased effort of turning multiple crankshafts against more valve springs is offset by the inherent advantages of the overhead cam design.