Using natural gas/hydrogen mixture as a fuel in a 6-cylinder stoichiometric spark ignition engine

Hydrogen added to natural gas improves the process of combustion with the possibility to develop engines with higher performance and lower environmental impact. In this chapter, experimental analyses on multi-cylinder heavy duty engines, fuelled with natural gas-hydrogen blends, are reported. Theoretical aspects on engine performance are illustrated and a formula to evaluate the benefit of H2 addition on NG combustion is defined. Experimental data on the effects of air index and exhaust gas recycling on combustion with different NG/H2 blends are discussed followed by an experimental comparison of stoichiometric and lean-burn strategies on the European transient cycle for heavy duty emission certification. Results of the study indicate that a right metering of hydrogen into the natural gas and an optimization of the charge dilution provides not only a reduction in tailpipe CO2 emissions and a more complete combustion process with a lower formation of THC and CO, but also a possible increase in engine efficiency, avoiding abnormal combustion phenomena.