Why does thermal efficiency increases with compression ratio?

As the compression ratio increases, the fuel mixture is sufficiently compressed thereby increasing the thermal efficiency, so that less fuel is required to produce the same amount of energy. Fuel consumption is reduced at higher compression ratios between 8 and 9.

What is the effect of compression ratio on thermal efficiency?

The thermal efficiency increases and the brake specific fuel consumption decreases with the increase of compression ratio. The higher compression ratio results in higher in-cylinder pressure and higher heat release rate as well as lower ignition delay.

What happens when you increase the compression ratio of an engine?

All things equal, engines with higher compression ratios require higher fuel octane. This is because a lower octane fuel may begin to ignite prior to the initiation of the spark event through the ignition system, a condition known as detonation or auto ignition.

Why does high compression make more power?

As the piston of each cylinder moves down the bore, the drop in pressure follows a distinctly different line. The 15:1 cylinder drops pressure much faster than its 2:1 counterpart because of its more rapid change in volume. From this you can see why a high-compression cylinder produces better power and fuel economy.

What is thermal efficiency in an engine?

Figure 1: The amount of work output for a given amount of heat gives a system its thermal efficiency. Heat engines turn heat into work. The thermal efficiency expresses the fraction of heat that becomes useful work.

How do you calculate thermal efficiency from compression ratio?

Thermal Efficiency for Otto Cycle In this equation, the ratio V1/V2 is known as the compression ratio, CR. When we rewrite the expression for thermal efficiency using the compression ratio, we conclude the air-standard Otto cycle thermal efficiency is a function of compression ratio and κ = cp/cv.

Why does higher compression make more power?

This occurs because internal combustion engines are heat engines, and higher compression ratios permit the same combustion temperature to be reached with less fuel, while giving a longer expansion cycle, creating more mechanical power output and lowering the exhaust temperature.

What is the volumetric efficiency of compression?

The volumetric efficiency of a compressor is defined as the ratio of actual volume sucked by the compressor at the inlet to the swept volume. volumetric efficiency is given by, η v = 1 + c − c ( P 2 P 1 ) 1 n.