Natural gas injection to the four-stroke engine as fuel is a direct route of fuel distribution system. With pretreatment of natural gas, it gains the quality condition that meets fuel standards. Regular four-stroke engines present in automobiles use nitromethanol, dimethylether, gasoline, biodiesel and diesel liquid fuel. When gaseous fuel counts, liquefied petroleum gas obtained from petroleum refinery in the process of rectification of crude used in domestic and medium-heavy vehicles. The above fuels storage, vehicle filling and utilizing systems are developed with safety factors and designed for specific mechanical engines.
Two more fuels that are gaseous, compressed natural gas and hydrogen are in the queue for automobile four-stroke engines. A study says that when compressed natural gas is ignited in the combustion chamber of a four-stroke engine 325 chemical reactions take place at an instant. Similarly, when hydrogen is combusted it undergoes 23 chemical reactions. These two fuel well suitable for compression ignition engines with storage kits of less weight. This helps the performance of the engines and vehicle by the dropped weight of the hydrogen storage kit and mainly to the torque produced by the engine.
Compression system of gaseous fuel described by and named as
- Premixed compression ignited combustion
- Active thermo-atmosphere combustion
- Premixed direct injection combustion
- Lean homogeneous combustion
- Multiple stage combustion
- Compression ignited homogeneous charge combustion
- Homogeneous charge compression ignition
- Active radical combustion
The above methods all work on same theory containing the concept of increasing thermal efficiency. The drawbacks and benefits are based on the factors in each method that are evaluated by fuel rich zones, time delay of ignition, composition ratio of fuel and air, temperature generated during combustion, particulate emission, NOx compounds formation and knocking.