The dual fuel engine works on diesel cycle. As the name suggests two fuels come into use.The gaseous fuel, which is the primary fuel (usually air/natural gas) is first compressed and then the pilot fuel(small quantity of liquid fuel) is injected for the rapid combustion. The total working of the engine is described under the working heading. Thus as two fuels are being used for the engine power this is called dual fuel engine.

The dual fuel engine is the combination of both Otto and diesel engine. Firstly going to the concept, the otto cycle is constant volume cycle and diesel cycle is constant pressure cycle. Now, these cycles are theoretically enough correct but in practice they become unreal.

For the chemical reaction to take place during the combustion process, some time interval is required. Hence the combustion process doesn’t occur at constant volume.

Also Read: What will happen If we use Petrol in Diesel Engine or Vise Versa?

Likewise in diesel cycle, due to uncontrolled combustion, the process doesn’t take place at constant pressure. Thus dual cycle which is also called as limited pressure cycle is a combined Otto and diesel cycle.


In the dual cycle, some amount of heat is added at constant volume and some at constant pressure. (Qs) as shown in the diagram is heat addition.

                          dual fuel engine

1-2: reversible adiabatic compression

2-3: constant volume heat addition

3-4: constant pressure heat addition

4-5: reversible adiabatic expansion

5-6: constant volume heat rejection

Working Of The Dual Fuel Engine-