Diesel engines are known for their superior fuel efficiency compared to petrol engines. This is because diesel fuel has a higher energy density than petrol, meaning that it contains more energy per unit of fuel. This results in diesel engines being able to extract more energy from each litre of fuel, leading to better fuel efficiency.
One of the reasons diesel engines are more fuel efficient than petrol engines is that diesel fuel has a higher calorific value. This means that it contains more energy per unit of volume than petrol. Diesel fuel is also more dense than petrol, which means that a given volume of diesel fuel contains more energy than the same volume of petrol. This means that diesel engines can extract more energy from each litre of fuel, leading to better fuel efficiency.
Another reason for the higher fuel efficiency of diesel engines is that they have a higher compression ratio than petrol engines. Diesel engines compress the air in the combustion chamber to a much higher degree than petrol engines, which results in a higher temperature and pressure when the fuel is injected. This high compression ratio and resulting high temperature and pressure in the combustion chamber lead to a more complete combustion of the diesel fuel, resulting in less wasted energy.
In addition, diesel engines typically have a leaner air-fuel mixture than petrol engines. This means that there is more air and less fuel in the combustion chamber, resulting in a more efficient combustion process. Diesel engines also use direct injection, which means that the fuel is injected directly into the combustion chamber, rather than into the intake manifold as in petrol engines. This results in more precise fuel metering, which also contributes to better fuel efficiency.
Finally, diesel engines also have a longer stroke than petrol engines. The stroke is the distance the piston travels from top dead center to bottom dead center. A longer stroke allows for a greater volume of air to be drawn into the engine and compressed, resulting in a more efficient combustion process. This contributes to the higher fuel efficiency of diesel engines.
In conclusion, diesel engines are more fuel efficient than petrol engines because diesel fuel has a higher energy density, diesel engines have a higher compression ratio, a leaner air-fuel mixture, direct injection, and a longer stroke. These factors all contribute to diesel engines being able to extract more energy from each litre of fuel, resulting in better fuel efficiency. As fuel efficiency is becoming more important for environmental reasons, the popularity of diesel engines is expected to continue to grow.