Performance and emissions of hydrogen-diesel dual direct injection (H2DDI) in a single-cylinder compression-ignition engine

Abstract

Hydrogen-diesel dual direct-injection (H2DDI) is successfully implemented in a compression-ignition engine, which is developed to circumvent the pre-ignition and knocking limitations inherent to port fuel-injection hydrogen engines. An automotive-size single-cylinder common-rail diesel engine was modified to fit an additional high-pressure hydrogen injector in the cylinder head. The engine is operated at intermediate load with constant fuel-energy input using an energy-substitution principle – the diesel injection duration is decreased as the hydrogen amount is increased while adjusting the diesel injection timing to fix the combustion phasing. The results show that, at early hydrogen injection timings, the heat release rate and engine-out emissions show trends indicating premixed combustion whereas later injection timings exhibit hydrogen mixing-controlled combustion behaviour. At 50% hydrogen substitution ratio and optimised direct injection timing of 40 ⁰CA bTDC, the uncompromised indicated efficiency of 47% is achieved while the combustion-induced noise is decreased by 6 dB and the engine-out NOx emission is kept below 11 g/kWh.