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

<div class="section abstract"><div class="htmlview paragraph">Nowadays, hydrogen (H2) is rising as a key solution to fuel internal combustion engines (ICE) since it allows carbon free combustion process. At the same time, ICE fueled with H2 can reach similar performance and driving experience of gasoline fueled ones. In stoichiometric conditions, hydrogen shows higher flame speed, lower ignition energy and lower quenching distance than gasoline. Mainly for these reasons, H2 combustion is characterized by a high risk of abnormal combustion (i.e. knock and pre-ignition), relevant NOx emissions and high heat losses. On the other hand, the wide 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, to assess the benefits of three mixture dilution methods. 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 their effectiveness on engine thermal efficiency and NOx emissions. Enleanment has a relevant impact on the size of the turbocharger system, cEGR affects the engine total heat rejection, while WI requires dedicated injection system and tank. Therefore, each dilution strategy requires a dedicated hardware optimization. In this regard, 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 and heat rejection at low-medium loads.</div></div>