Why Are Diesel Engines Fuel-efficient?

It is well known that diesel engines are fuel-efficient, so the question is: Why are diesel engines so fuel-efficient? Some people say that it is because of the high calorific value of diesel, the design of small cylinder diameter and large stroke, and the high compression ratio. But fundamentally, it is because of the compression ignition combustion method of diesel engines. All factors that make diesel engines fuel-efficient are based on compression ignition.

Compression ignition can improve the thermal efficiency of diesel engines in the following aspects, thereby reducing fuel consumption:

1. Compression ignition requires a higher compression ratio

The so-called compression ignition is to compress a large amount of air violently so that its temperature exceeds the auto-ignition temperature of diesel, so that diesel can ignite itself. If you want to compress air to a very high temperature, you need a large compression ratio. For internal combustion engines, the greater the compression ratio, the higher the thermal efficiency and the more fuel-efficient it is. Because the greater the compression ratio, the greater the pressure in the compression stroke cylinder, the greater the thrust on the piston when doing work, and the more energy converted.

2. Compression ignition can reduce pumping loss

Pumping loss is the power lost when the engine inhales and exhausts. When the engine inhales, it needs to suck air into the cylinder, and when it exhausts, it needs to push the exhaust gas out of the cylinder. This seemingly simple process will consume a lot of power at a high engine speed of several thousand revolutions per minute. The characteristics of compression ignition of diesel engines determine that its pumping loss is naturally lower than that of gasoline engines.

3. Compression ignition is naturally equipped with lean combustion function

Lean combustion is a technology that uses very little fuel to maintain engine operation when the power demand is not very large, which can reduce fuel consumption. Diesel engines are naturally equipped with the ability of lean combustion, because of the combustion method of compression ignition of diesel engines, when working, you can spray as much fuel as you want, as long as the temperature in the cylinder is high enough, you can ignite and work, which is an innate advantage.

So the most fundamental factor for diesel engines to save fuel is the compression ignition method.