What is the typical compression ratio for a diesel engine?

The typical compression ratio for a diesel engine generally falls between 14:1 and 25:1. This higher compression ratio is a fundamental characteristic of diesel engines, which allows them to achieve the necessary cylinder temperatures for fuel ignition without the need for spark plugs. The increased compression is essential for the efficient combustion of diesel fuel, which is denser and requires higher pressures to ignite compared to gasoline.

This range is indicative of the diesel engine's design, where higher compression leads to better thermal efficiency and power output. The ability to operate under high compression supports the diesel cycle's principles, which leverage thermodynamic efficiency to extract maximum energy from the fuel.

In contrast, lower compression ratios, as suggested in the other options, do not reflect the typical characteristics of diesel engines, while saying it varies greatly depending on the model introduces more variability than is common for diesel engine design, which tends to be more standardized concerning compression ratios.