Gasoline engines work by compressing a mixture of fuel and air, then igniting it using a spark plug. But compress the mixture too much and it can prematurely self-ignite, which causes destabilizing engine knock. Diesel’s invention avoids that problem by compressing only the air, and more so, making it hot enough to ignite the fuel when it’s injected. This allows the engine to be more efficient: the higher the compression, the less fuel is needed.
