On the improvement of performance and pollutant emissions of a spark ignition engine fuelled by compressed natural gas and hydrogen

This paper presents the results of an experimental and a theoretical investigation made by simulations on a Renault HR09DET spark ignition engine, four-stroke, 3-cylinders, multipoint fuel injection fuelled successively by gasoline and compressed natural gas and hydrogen. The simulation model, developed with the AVL Boost program was calibrated using the experimental data obtained for a spark ignition engine fuelled with gasoline. The experimental data obtained on an engine test bench were compared with simulation results for gasoline and compressed natural gas fuelling. The simulation model allowed the addition of hydrogen in parallel with the fuelling by natural gas. The results highlight the advantages and disadvantages of operating a spark ignition engine with hydrogen enrichment of natural gas, in terms of regulated emissions as unburned hydrocarbons (HC), carbon monoxide (CO) and nitrogen oxide emissions (NOx). As the amount of hydrogen in the mixture increases, up to 20%–30% volumetric fractions an extend in the combustion limits occurs associated to consistent reductions up to 65% for HC and 55% for CO. A slight decrease by an average of 15% occurs in NOx emissions for stoichiometric mixtures compared with gasoline. Considering the higher-octane number for Compressed Natural Gas (CNG) and hydrogen, the engine efficiency can be significantly improved by increasing the compression ratio up to the knock limit.