An experimental investigation of exhaust emissions of a 1999 Cummins ISM370 diesel engine supplemented with H2

This paper investigates the effect of hydrogen (H2) addition on the exhaust emissions of a 1999 Cummins ISM370 heavy-duty diesel engine with H2 continuously supplemented to intake air. Using the 13-mode European Stationary Cycle (ESC), the addition of 2 per cent H2 by volume increased the emissions of oxides of nitrogen (NOx) and nitrogen dioxide (NO2), but reduced nitric oxide (NO) emissions. The addition of 4 per cent H2 increased the emissions of NO, NO2, and NOx. When examined under constant load, the addition of H2 reduced the emissions of particulate matter (PM) and carbon monoxide (CO), but had very mild effects on hydrocarbon (HC) emissions. It was also shown that the reduction in PM emissions was due to the reduced diesel fuel flowrate rather than the improvement to the combustion efficiency of diesel fuel. However, the addition of a relatively large amount of H2 at medium to high (30–70 per cent) load substantially increased the emissions of NOx. This was due to an increase in maximum local combustion temperature resulting from the enhanced heat release rate, advanced combustion phasing, and reduced combustion duration. In comparison, the addition of a small amount of H2 had a very mild effect on NOx emissions. However, a substantial reduction in NOx emissions was observed with the addition of large amounts of H2 at 10–15 per cent load, which was due to deteriorated peak heat release rate observed at premixed combustion process and elongated diffusion combustion process, which reduced the peak local combustion temperature and retarded the combustion phasing. It was also noted that the addition of H2 substantially increased the emissions of NO2, indicating the significant effect of H2 addition in enhancing the conversion of NO to NO2. When measured using the 13-mode ESC, the addition of 2 per cent and 4 per cent H2 increased NO2 emissions by 300 per cent and 221 per cent, respectively. When measured under constant load, a maximum NO2/NOx ratio of 62.2 per cent was obtained with the addition of 4 per cent H2 at 10 per cent load.