Hydrogen assisted jet ignition for near elimination of NOx and cyclic variability in the S.I. Engine

The performance of a combustion initiation system for the Otto cycle engine is described which uses a pre-chamber of 1.5% main chamber clearance volume, fuelled with minute quantities of hydrogen. The order of magnitude faster flame kernel growth, obtained with hydrogen mixtures compared with hydrocarbon fuels, provides enhanced jet momentum from a small proportion of the total charge energy, and active radicals and intermediate species which assist in initiating combustion in mixtures significantly leaner than the lean flammability limit with normal ignition. The performance results demonstrate the ASTM CFR engine working at up to 70% maximum torque with NO x emissions close to ambient levels. The hydrogen assisted jet ignition, HAJI, use to achieve this also confers extremely stable combustion with coefficients of variation of peak cylinder pressure and specific work per engine cycle reduced by 50 to 80% from those normally achieved with this engine. This allows increased thermal efficiency at ultra lean operation, at relative air/fuel ratios of around 2, and about two numbers increase in the highest useful compression ratio. There is no lean limit of combustion within the range of usable engine torque. Operation with relative air/fuel ratios of 5 have been achieved. With methanol as the main chamber fuel, the results presented here demonstrate an improvement in maximum indicated thermal efficiency of 15 per cent simultaneously with the low NO x emissions. The hydrocarbon emissions remain high which is a characteristics of this research engine.