The Effect of CNG Conversion in Reducing the Exhaust Emissions of Inner-City Vehicles
In the present article, the emission analysis of a bi-fuel spark ignition engine is investigated. A sample car is used for experimental tests. The car is originally gasoline-fuelled. It is converted to a bi-fuel vehicle by installing necessary components. After conversion, it may run both on natural gas and gasoline. The exhaust emissions are measured before conversion, and are assumed as the base emission values. After the conversion, similar emission tests are carried out for both gasoline and natural gas conditions with closed-loop and open-loop gas supplying systems. The effects of conversion parameters on emission values are fully discussed. It is understood that the gas/air mixer plays a significant role in emission values of a converted engine. Furthermore, determination of ? parameter, which is the ratio of actual to stochiometric air/fuel ratio, is very important. The results of closed-loop and open-loop conditions are compared. The influence of ignition timing on the emission values is discussed. It is known that natural gas needs more timing advance than gasoline in order to have complete combustion. The optimum timing advance for natural gas is obtained through laboratory experiment. This optimum value may differ from one engine to another one. The emissions of the converted vehicle are compared with the base emission values for a series of engine speeds. It is observed that the exhaust pollutants of the converted vehicle in CNG operation decrease in comparison with the base emission values. The scientific reasons are presented to validate the results.