A Numerical Study on Effect of Ignition Timing and Mixing Ratio of Natural Gas Spark Ignition Engine on Engine Performance and Exhaust Emission Characteristics

Abstract

Interest in natural gas as an internal combustion engine fuel has been renewed due to its increasing domestic availability and stable price relative to other petroleum fuel sources. Natural gas, comprised mainly of methane, allows for up to a 25% reduction in engine out CO2 emissions due to a more favorable hydrogen-to-carbon ratio, relative to traditional petroleum sources. Traditional methods of injecting natural gas can lead to poor part-load performance, as well as a power density loss at full load due to air displacement in the intake manifold. Natural gas direct injection, which allows the fuel to be injected directly into the cylinder, leads to an improvement in the in-cylinder charge motion due to the momentum of the gaseous injection event. In this study, the potential improvement in thermal efficiency and emission characteristics of SI engines fueled with natural gas running with various ignition timing was investigated. The engine was tested at 1800 rpm, volume percent of propane in the methane propane blends ranged from 0 to 20%. Performance tests were performed via measuring brake thermal efficiency, brake specific fuel consumption, cylinder pressure and exhaust emissions (CO, THC, NOx). The use of natural gas as an alternative fuel is a promising solution. The potential benefits of using natural gas in SI engines are both economic and environmental. Chemical kinetic simulation of natural gas combustion has been carried out based on available literature data. Comparative results are given for various ignition timing and various mixing ratio, revealing the effect of ignition timing, and mixing ratio on engine performance and exhaust emissions.