What effect does increasing the compression ratio have on combustion efficiency?

Increasing the compression ratio in an engine generally enhances combustion efficiency, but only up to a certain point. As the compression ratio rises, the engine can extract more energy from the fuel-air mixture by compressing it more, leading to a higher temperature and pressure before ignition. This results in a more complete combustion process and improves overall thermal efficiency.

However, it's important to note that this increase in efficiency is not limitless. Beyond a specific threshold, further increases in the compression ratio can lead to issues such as knocking or pre-ignition. These problems occur when the fuel ignites prematurely due to excessive compression, ultimately reducing efficiency and potentially damaging the engine.

Thus, while a higher compression ratio can lead to increased combustion efficiency, there's an optimal range where benefits are reaped before diminishing returns or negative consequences occur.