Today's SI engines typically operate at which range of compression ratios?

The correct range of compression ratios for today’s spark ignition (SI) engines is between 8:1 and 11.5:1. This range is standard for most modern gasoline engines, as it balances efficiency and performance. Higher compression ratios can lead to better thermal efficiency and increased power output. However, they also require higher-octane fuels to prevent knocking or pre-ignition, a concern that engineers address through combustion chamber design and fuel management systems.

Engines in this compression ratio range are optimized for a combination of power, efficiency, and emissions control. As technology has advanced, many manufacturers have been able to design engines that operate effectively at these ratios while still meeting stringent environmental regulations.

Other ranges listed do not reflect the current technologies in SI engine designs; for example, lower ranges such as 6:1 to 9:1 and 5:1 to 7:1 are typical of older engines or those designed for specific low-performance applications. The 10:1 to 14:1 range, while it may apply to high-performance engines, is generally not typical for the average modern SI engine, as it would necessitate special considerations for fuel type and engine knock.