Potentials of the Oversizing and H2-Supported Lean Combustion of a VVA SI Gasoline Engine towards Efficiency Improvement

In recent years, internal combustion engine (ICE) downsizing coupled with turbocharging was considered the most effective path to improve engine efficiency at low load, without penalizing rated power/torque performance at full load. On the other side, issues related to knocking combustion and excessive exhaust gas temperatures obliged adopting countermeasures that highly affect the efficiency, such as fuel enrichment and delayed combustion. Powertrain electrification allows operating the ICE mostly at medium/high loads, shifting design needs and constraints towards targeting high efficiency under those operating conditions. Conversely, engine efficiency at low loads becomes a less important issue. In this track, the aim of this work is the investigation of the potential of the oversizing of a small Variable Valve ActuationSpark Ignition gasoline engine towards efficiency increase and tailpipe emission reduction. To enhance the potential improvements of such an approach, a lean combustion concept is adopted, where the flame speed propagation is supported by doping gasoline with the addition of a percentage of hydrogen (10% by mass). The analysis is carried out by a 1D simulation tool, widely validated for the base engine supplied with pure gasoline and under stoichiometric/rich combustion. The combustion and knock models are here extended to handle the flame speed and auto-ignition characteristics of gasoline/H2 blends. The comparison between the base gasoline engine and the oversized gasoline/H2 variant highlights significant efficiency advantages at full load operations, which are due to the possibility to remove fuel enrichment and combustion delays. Exceptfor unburned hydrocarbons, pollutants and CO2 emissionsare reducedthanks to the synergic effects of H2addition and ultra-lean mixtures. A certain penalization of efficiency arises at very low loads, where engine oversizingdegrades the combustion process.