The dual fuel engine works on compression ignition principle. At first the air-fuel is drawn into the engine cylinder which is highly compressed in the cylinder. Next step is the ignition process. But this fuel (also called gaseous fuel) is not a good compression ignition fuel. Hence a small amount of diesel (called as pilot fuel) is injected, which acts as a catalyser to the ignition process. As the fuel is ignited due to the temperature rise, the whole air-fuel mixture ignites and rapid combustion takes place. Due to this rapid combustion the pressure inside the cylinder is increased causing the piston to move and produce engine power.
The sudden increase in the dual fuel engine causes knocking problem, which can be controlled by injecting a definite quantity of diesel fuel.
One intresting fact about the dual fuel engine is that the combustion takes place as a CI engine fashion, but the propagation of the flame front is just like the SI engine.The air standard efficiency for any engine is given by, the ratio of Heat added minus heat rejected to total heat added.
The mathematical formula for the efficiency is given as,
The efficiency of the dual fuel engine lies between the Otto and Diesel cycle.
When the rc (cut-off ratio) is equal to 1, it becomes an otto engine and when the rp (pressure ratio) is equal to 1, it becomes a diesel engine.
- Less fuel usage i.e., as the cost of diesel fuel is more converting an engine to work on air and a small amount of diesel is economical.
- Spark plug and ignition system is not required.
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