Natural Gas/Hydrogen blends for heavy-duty spark ignition engines: Performance and emissions analysis

In view of the strong interest in the adoption of hydrogen as an alternative fuel for internal combustion engines, the authors present the results of an experimental activity aimed at evaluating the effect of hydrogen use on performance and emissions of a heavy-duty (HD) spark ignition engine. The engine, installed on a test bench and working with compressed natural gas (CNG) in its standard version, has been fed with blends of CNG and H2, at various percentages (15% and 25% of H2 by volume) and tested in steady-state and transient driving conditions. The analysis in steady state was performed in two working modes: at the same combustion barycentre and at the same nitrogen oxides (NOx) emissions of the pure CNG case, by means of proper spark advance calibrations. A detailed combustion and emissions analysis were performed, highlighting a coherent response of the engine to the replacement of CNG with H2. The NOx increment tendency is easily counteracted by reduced SA settings, while total hydrocarbons and carbon oxides emissions reduction were measured when the blends were burnt. Consistent carbon dioxide emission mitigation was revealed, mainly in transient conditions, operated at the same ECU calibration of the pure CNG case. The main novelty of the work is in providing an in-depth study of the engine behaviour to hydrogen addition in transient condition. The response of engine management system to different fuels when rapid speed and torque variations occur, were evaluated. In this sense, the study offers detailed information on the feasibility of the use of hydro methane in existing engine architecture; such mixtures can represent, in the next future, a probable fuel option in view of the oncoming decarbonization process. Moreover, new insights on particle emission burning hydro-methane are presented. The results of engine-out PN emissions along a transient cycle revealed a correlation between particle emissions spikes with specific phases of the driving cycle and a trend in PN reduction in case of hydrogen addition.