Which of the following engines ignites fuel through compression rather than via a spark?

The correct answer is the Diesel Engine. Diesel engines operate on the principle of compression ignition, where air is compressed to a very high pressure, creating a significant rise in temperature. When diesel fuel is injected into this highly compressed and heated air, it ignites spontaneously without the need for a spark plug. This process is efficient and allows diesel engines to achieve higher thermal efficiency and greater torque at lower RPMs compared to gasoline engines, which rely on spark ignition.

In contrast, spark ignition engines, including gasoline engines, utilize a spark plug to ignite a fuel-air mixture at a specific point in their cycle. Electric engines differ fundamentally from combustion engines as they do not involve any fuel combustion process at all, thus having no need for either spark or compression ignition. Understanding these distinctions is key for grasping the mechanics and operational principles of various engine types.