Compressed Natural Gas Direct Injection: Comparison Between Homogeneous and Stratified Combustion

Abstract

Due to abundance of natural gas, the use of natural gas for automotive use, particularly for internal combustion engine (ICE), is more practical and cheaper than their future successors. Even though natural gas is a cleaner fuel than other fossil fuels and has a higher octane number and can lead to higher thermal effiency, its low carbon number makes it less attactive as compared to gasoline and diesel. Based on its potential, an engine referred to as compressed natural gas direct injection engine (CNGDI) was designed, developed and tested to operate on compressed natural gas (CNG) as monofuel directly and centrally injected into the engine. Computational and experimental works have been performed to investigate the viability of the design. Computational flid dynamics (CFD) simulations and experimental works with homogenous combustion showed that the results were in good agreement. From experimental works, it is found that combustion characteristics could be improved by using a stratifid charge piston confiuration with some drawback on performance. In terms of exhaust emissions, stratifid confiuration causes slight increase in the emission of CO, CO2 and NOx, which highlight a need for further study on this issue.