How does higher compression ratio affect an engine's efficiency?

A higher compression ratio in an engine enhances its thermal efficiency. This improvement occurs because increasing the compression ratio allows the engine to extract more energy from the fuel-air mixture during combustion. When the mixture is compressed to a smaller volume before ignition, it results in a more complete combustion process, which leads to a higher pressure and temperature inside the combustion chamber, allowing for more energy to be converted into useful work.

Higher thermal efficiency means that the engine can extract more energy from the same amount of fuel, leading to an increase in overall performance and fuel economy. This principle is consistent with the thermodynamic theory that states that the efficiency of a heat engine increases as its compression ratio increases, up to a certain point. Beyond that limit, diminishing returns may occur due to factors like engine knock or the need for higher-octane fuels, but in general, the impact on efficiency remains positive up to optimal levels.

In contrast, a decrease in efficiency, no significant impact, or increased noise levels are not associated with higher compression ratios; instead, those scenarios would relate more to different engine characteristics or design limitations.