Natural gas as Alternate fuel:
Natural gas is produced from gas wells or tied in with crude oil production. Natural gas (NG) is made up primarily of methane (CH4) but frequently contains trace amounts of ethane, propane, nitrogen, helium, carbon dioxide, hydrogen sulphide, and water vapour. Methane is the principal component of natural gas. Normally more than 90% of natural gas is methane.
Natural gas can be compressed, so it can stored and used as compressed natural gas (CNG).
CNG requires a much larger volume to store the same mass of natural gas and the use of very high pressure on about 200 bar or 2,900 psi.
Advantages of CNG:
1. Natural gas is safer than gasoline in many respects.
2. The ignition temperature for natural gas is higher than gasoline and diesel fuel.
3. Natural gas is lighter than air and will dissipate upward rapidly if a rupture occurs.
4. Gasoline and diesel will pool on the ground, increasing the danger of fire.
5. Compressed natural gas is non-toxic and will not contaminate groundwater if spilled.
6. Compressed natural gas is a largely available form of fossil energy and therefore non-renewable.
7. It is a cleaner fuel than either gasoline or diesel as far as emissions are concerned. Fuel Characteristics of CNG:
The octane rating of natural gas is about 130,meaning that engines could operate at compression ratio of up to 16:1 without “knock” or detonation. Many of the automotive makers already built transportation with a natural gas fuelling system and consumer does not have to pay for the cost ofconversion kits and required accessories. Mostimportantly, natural gas significantly reduces CO2emissions by 20-25% compare to gasoline becausesimple chemical structures of natural gas (primarilymethane – CH4) contain one Carbon compare to diesel(C15H32) and gasoline (C8H18). Like methane and hydrogen is a lighter than air type of gas and can beblended to reduce vehicle emission by an extra 50%.Natural gas composition varies considerably over tim eand from location to location. Methane content istypically 70-90% with the reminder primarily ethane, propane and carbon dioxide. At atmospheric pressure and temperature, natural gas exists as a gas and has low density. Since the volumetric energy density(joules/m3) is so low, natural gas is often stored in a compressed state (CNG) at high pressure stored in pressure vessels.
CNG Ideal operation:
Injection methods of Natural Gas engine
There are four methods to inject the NG into the engine cylinder. First type is gas mixer / carburetor injection, second type is the single point injection, third type is multi point injection and fourth type is direct injection. The illustration of the four methods of NG injection is shown in Fig.