Experimental and Numerical Investigation of Different Dilution Techniques in a High-Performance H2 - Fueled SI Engine

Nowadays Hydrogen (H2) fueled Internal Combustion Engine (ICE) can be considered a promising solution for high performance applications since it allows carbon free combustion process. At the same time, H2-ICE can reach similar performance and driving experience of gasoline engines. Compared to gasoline, Hydrogen combustion, in stoichiometric conditions, shows a higher flame speed, a lower ignition energy and a lower quenching distance. Mainly for these reasons H2 combustion is characterized by a high risk of abnormal combustion (Knock and Pre-Ignition), relevant NOx emissions and high heat losses. On the other hand, the high flammability range and high combustion stability of H2 allow the use of different techniques to reduce combustion reactivity. This work presents a combined approach experimental and numerical in order to assess the benefits and the disadvantages of each method. The experimental campaign, in different operating conditions, was carried out on a production derived high specific power gasoline Single Cylinder Engine (SCE) retrofitted to H2 with Direct Injection (DI). Three different dilution techniques were tested: enleanment, cooled Exhaust Gas Recirculation (cEGR) and manifold Water Injection (WI). The impacts on combustion of the different strategies were analyzed in order to evaluate the effectiveness on thermal efficiency and NOx emissions. Enleanment and cEGR have relevant impacts on the size of the turbocharger system and cooling system, while WI requires a dedicated injection system and a dedicated tank, therefore dilution strategies must be used as best as possible. Afterwords, a 1D-CFD simulation model of complete 6-cylinder engine was developed with the aim to assess the above-mentioned techniques in terms of fuel economy at low-medium loads.