Experimental Characterisation of Combustion, Performance, and Emissions in a Hydrogen Opposed Piston Engine

Hydrogen has demonstrated significant potential in the adoption of zero-carbon fuels for conventional internal combustion engine platforms. However, with multiple H₂ICE technologies being adopted across wider platforms, several limitations have been observed, including abnormal combustion phenomena such as pre-ignition and backfire, as well as modifications in engine operating regimes. These complications arise from the distinct combustion characteristics of hydrogen compared to carbon-based fuels, necessitating careful optimisation to ensure reliable and efficient engine performance. The study aims to assess the adoption of pure hydrogen direct injection technology on a radical two-stroke opposed-piston engine with a 15 crank degree phase shift to optimise the engine's capability for hydrogen adoption through Atkinson-like cycles, while improving scavenging and reducing the pre-ignition risk associated with hydrogen DI adoption. The engine provides a flexible platform that can operate in compression ignition and spark ignition, allowing it to adopt multiple fuels. Multiple experimental tests have been conducted to assess the hydrogen performance and emissions, starting from mid- and low-load spark sweeps to identify the minimum spark for best torque (MBT), followed by a complete map of the fuel matrix to study engine sensitivity and combustion stability over the injection map at low load. Therefore, lambda and load sweep tests have been conducted to assess burn characteristics and efficiency with wider air-to-fuel ratios. The study's outcomes demonstrate an impressive thermal efficiency of 58.7% at lambda 3.2, with an indicated mean effective pressure (IMEP) of 500 kPa. Additionally, it exhibits lower NOx engine-out emissions, peaking at 863 ppm at the same load and lambda 1.38. Furthermore, the steady-state engine-out emissions analysers show near-zero carbon emissions over the wider operating tests.