Correlations of wiebe function parameters for combustion simulation in SI engine fuelled with gaseous fuels

Combustion simulation in SI engine fuelled with unconventional gaseous fuels becomes more necessary in last years. The reason is because the use of e.g. biogases from anaerobic digester process or gasification of biomass to produce "green energy". From the view of energy balance of small CHP units, the SI engine seems to be most efficient appliance as a part of this unit. Through 1D, simulation of in-cylinder pressure a fast prediction of engine performance is possible. In this case, the Mass Fraction Burn (MFB) function can be used. The MFB reflect the amount of fuel burned throughout the combustion process in an internal combustion engine. SI engine combustion simulation by using a Wiebe function to represent the MFB is very often used in a 1D-engine code that allow for fast calculations and a good accuracy of results. This paper deals with calculations of Wiebe function coefficients based on experimental data of four stroke naturally aspirated SI engine fuelled with natural gas and simulated producer gas. The Wiebe function parameters are determined over a range of fuel compositions and air excess ratio by fitting the Wiebe function curve to the experimentally obtained MFB data from a single-zone Heat Release Rate (HRR) analysis.