USING A STAND ALONE MODEL TO INVESTIGATE KNOCK CRITERION IN AN SI GAS ENGINE FUELED WITH METHANE

Natural Gas has been widely considered as an alternative fuel for internal combustion, since it is a major source of fuel after crude oil products and is capable to meet low emission standards specially CO2. In this paper combustion phenomenon of natural gas in from of methane is studied in detail. Knock limits compression ratio and spark timing in SI engines; that would directly affects the thermal efficiency and output power and may be the cause of mechanical damage in engine. In this paper, a two zone thermodynamic model is developed using a chemical kinetics mechanism with 20 reactions and 15 chemical species for methane combustion. It is assumed that the flame, with adiabatic temperature is in equilibrium stage. The unburned zone is considered extensively to analyze the conditions that lead to knock. The “Knock Criterion” has been used to forecast the knock intensity. The influence of engine parameters such as spark advance, compression ratio and relative humidity of air intake is studied on knock phenomenon. The experimental engine results from reference works are used to validate the accuracy of our model.

Keywords:

Internal Combustion Engine , Methane , Knock , Two-zone Thermodynamic Modeling , Chemical Kinetics