A Technical Review of Optimisation Natural Gas SI Engine with employing EGR rate.

The research on alternative fuels for internal combustion engine has become essential due to depletion of petroleum products and its major contribution for pollutants, where Natural gas is one of the most promising fuel alternatives for the future. Compressed natural gas (CNG) has long been used in stationary engine as well as a transport engine fuel. There are various methods which use the compressed natural gas in IC engine with little modification. It is revealed that the performance characteristics are lower while the emission characteristics of CO, CO2 HC are better for Natural gas compared to petrol or diesel. The compression ratio has a large influence on the engine performance, combustion, and emissions. However, the brake thermal efficiency is increased with a compression ratio up to a limit of 12 at high engine loads. The maximum cylinder gas pressure is increased with increase in the compression ratio. The exhaust hydrocarbon (HC) and carbon monoxide emissions decreased with increase in the compression ratio, while the exhaust nitrogen oxide (NOx) emission is increased with increase in the compression ratio. In this study, a natural gas spark-ignition engine employing cooled exhaust gas recirculation (EGR) strategy in a high pressure inlet condition was optimized. Both engine compression ratio and start of combustion timing were optimized in order to obtain the lowest fuel consumption accompanied with high power and low emissions. It was found that cooled EGR can significantly reduce NOx emission at high compression ratio conditions.