Diesel VS gas

How does an engine work?

First of all, it is important to know how a car engine works. There are 4 cycles in its operation.

1)      Admission: The cylinder comes down and sucks air via the admission valves.

2)      Compression: The exhaust valves are closed. The piston comes up and compresses the gases. In a gas engine, these gases are made of a mix of air and fuel. However, in a Diesel engine, there is only air.

3)      Combustion: In a gas engine, the compressed gases are lit up by a spark created by a spark plug and a flame spreads. In a Diesel engine, the fuel is injected and because of the thermodynamic conditions in the combustion chamber (pressure and temperature), it ignites immediately without the intervention of a spark plug. In both cases, the combustion causes an increase in pressure and temperature that pushes the piston down.

4)      Exhaust: When going back up, the piston pushes the burned gases via the exhaust valves.

How are Diesel engines able to be more fuel efficient than gas engines?

There are many factors that influence global engine efficiency in Diesel engines.

First, Diesel has higher energy density than gas. In short, it means that 1 L of Diesel produces more energy in MJ (megajoule) than 1 L of gas. However, Diesel tends to gel more easily than gas which can be problematic for starting the engine in cold weather. To prevent this, our fuel filter heaters and oil pan heaters are affordable, easy to install solutions.

Then, the compression rate of a Diesel engine is higher. Earlier, we explained that ignition in such engines depends on the pressure and temperature inside. So, the higher the compression rate, the higher the efficiency.

The combustion chamber of Diesel engines also helps fuel efficiency. Indeed, there are less heat exchanges with the cylinder and the cooling fluid in a Diesel engine because of its bowl shaped piston. This represents a gain in useful energy over gas engines.

By design, Diesel engines do not need a throttle body like gas engines do. A throttle body is a kind of valve whose function is to regulate the air present in the cylinder by making the pressure drop and let the necessary air in for combustion in a stoichiometric mix. It also provokes a loss of charge at the admission (the entrance is blocked and the piston sucks the air while descending). Therefore, the engine struggles to fill itself and this has a negative impact on its efficiency. Diesel engines do not need a throttle body since there is always more air than necessary inside the engine to burn a certain quantity of fuel. This difference in architecture prevents the loss of charge at the admission found in gas engines.

Like we mentioned earlier, every Diesel engines work with a ‘’poor’’ fuel mix. Most gas engines, on the other hand, work with a stoichiometric fuel mix (however, this is beginning to change). The reason that most gas engines work with such a mix is because it is the only way the exhaust gases depolluting system will treat the fuel that arrives to it.

Finally, fuel efficiency in Diesel engines is helped by the fact that every Diesel engine is supercharged. A supercharged engine lets more air in the cylinder. So, for a determined engine rotation speed, it is able to burn more gas than a non-supercharged engine.

This concludes our first entry in our newest blog. Tell us your questions, comments, opinions in the Comments section!