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Natural gas composition depends on when and where it is recovered. Variations of composition affect the performance of combustion systems and the accuracy of delivered energy in fiscal gas metering. This paper presents a methodology to determine combustion properties of natural gases (higher heating value, Wobbe index and the stoichiometric air-fuel ratio). A pseudo-gas formulation is used to determine a composition of the most influent constituents of the natural gas. The pseudo-composition is then determined by solving a nonlinear system of equations using thermal conductivity at three levels of temperature and the carbon dioxide concentration. The tested natural gases are chosen to represent typical European gases as well as to account for large variations of individual components. The error on the combustion properties is less than 0.5% for the most of the examined gases and below 1% for gases with high carbon dioxide fractions.

Based on a thermodynamic approach, an analysis of a dual fuel combustion, in this particular case Syngas-Diesel, in a CI engine is presented. The influence of fuel substitution on combustion characteristics and engine performances are highlighted. Ignition delay (ID) and combustion models were developed to compute combustion characteristics and exhaust gas emissions. The paper focuses on three combustion stages, each described by a Wiebe law. The developed model ascertains experimental values of the Rate Of Heat Released (ROHR) at different loads and at various substitution rates of diesel fuel. Moreover, an Arrhenius equation law is used to predict NOx emissions. Good agreement with experimental data has been achieved between predicted and experimental data.