Piston Geometries Impact on Spark-Ignition Light-Duty Hydrogen Engine

Abstract

<div class="section abstract"><div class="htmlview paragraph">The European Union aims to be climate neutral by 2050 and requires the transport sector to reduce their emissions by 90%. The deployment of H<sub>2</sub>ICE to power vehicles is one of the solutions proposed. Indeed, H<sub>2</sub>ICEs in vehicles can reduce local pollution, reduce global emissions of CO<sub>2</sub> and increase efficiency. Although H<sub>2</sub>ICEs could be rapidly introduced, investigations on hydrogen combustion in ICEs are still required. This paper aims to experimentally compare a flat piston and a bowl piston in terms of performances, emissions and abnormal combustions. Tests were performed with the help of a single cylinder Diesel engine which has been modified. In particular, a center direct injector dedicated to H<sub>2</sub> injection and a side-mounted spark plug were installed, and the compression ratio was reduced to 12.7:1. Several exhaust gas measurement systems complete the testbed to monitor exhaust NO<sub>x</sub> and H<sub>2</sub>. Results were obtained for a specific operating point, 2000 rpm as engine speed and 13 bar as load, while sweeping the spark timing, the start of injection and λ. The spark timing sweep showed that the combustion with the bowl piston is faster than the one with the flat piston. The bowl piston also leads to stronger in-cylinder pressure gradients and higher exhaust emissions more likely due to mixture inhomogeneities. With respect to the start of injection, both pistons lead to similar results but for the H<sub>2</sub> emissions where the flat piston has the lowest levels. Finally, the sweep in λ, together with start of injection adjustments, also advantages the flat piston in terms of both performances and emissions. Nonetheless, adjusting either the spark timing or the start of injection with the bowl piston during a λ sweep allow to drastically reduce the NO<sub>x</sub> emissions. Abnormal combustions were captured with both piston but only with the lowest λ used.</div></div>