Influence of engine operating conditions on combustion parameters in a spark ignited internal combustion engine fueled with blends of methane and hydrogen

Abstract

An experimental study of the effects of hydrogen and methane proportions, Compression Ratio (CR) and equivalence ratio (∅) on the Knock Occurrence Crank Angle (KOCA), the Combustion Duration (ΔθCD) and the compression Polytropic coefficient (n) is carried out in this paper. These parameters were estimated through an alternative method that uses the average engine indicator diagram and the first derivative concept. The tests were conducted in a 2 kW Cooperative Fuel Research Engine (CFR) wherein the effect of inlet pressure on KOCA was also studied. To evaluate these effects, a factorial design of experiment and an one-factor Analysis of Variance (ANOVA) were conducted. According to the statistical analysis the evaluated engine operating conditions significantly influence the combustion parameters; however, the analysis revealed that the inlet pressure does not influence KOCA. Moreover, validated empirical correlations to estimate KOCA, ΔθCD and Critical Compression Ratio (CCR) as a function of engine operating conditions were proposed. It was demonstrated that actual Mass Fraction Burned (MFB) curves can be fitted with a = 2.8 and m = 2.4 which are the so-called efficiency and form factors of the Wiebe function, respectively. These values for hydrogen and methane mixtures are different from the values widely used for conventional fuels, i.e. a = 5.0 and m = 2.0. In the present study, the compression polytropic coefficients as a function of engine operating conditions were reported and were found to be ranging from 1.21 to1.25.