Effects of ozone addition on performance, combustion and emissions parameters on lean operation of a spark ignition engine fueled with Brazilian gasoline 2022-36-0050

The increasingly strict environmental legislations require the use of strategies and technologies to achieve higher efficiencies in internal combustion engines (ICE). In Brazil, governmental programs as Rota 2030 stimulate the development of technologies to improve engine efficiency and therefore promote fleet decarbonization. Due to lower carbon footprint, the use of renewable fuels as ethanol is an effective way to reduce greenhouse gas emissions. Nowadays, direct injection (DI) and variable valve timing (VVT) technologies are also used in modern downsized engines to reach higher thermal efficiencies with advanced strategies operation. As a significant part of energy losses in a spark ignition (SI) engine is caused by pumping work due to the method used for load control, operation in lean conditions have the potential to increase engine efficiency due to less pumping work requirement. In addition, NOx emissions are significantly reduced as lower combustion temperature is achieved with excess air. However, large ignition delays caused by slow flame kernel growth results in high cyclic combustion variability, limiting the maximum mixture dilution. In this context, ozone addition increases the reactivity of the mixture due to the pre-oxidation of fuel molecules, leading to a low temperature heat release, providing better ignition conditions and flame propagation to extend the lean limit operation. Thus, the focus of the present work is to explore air-dilution limits using ozone as a combustion enhancer at 1500 rpm in partial load operation. The experiments were performed in a turbocharged three-cylinder 1.0 L DI SI engine with variable cam timing, using gasoline E27 (Brazilian type C gasoline). Lambda was swept from stoichiometric to a maximum lean value considering 3% COV of IMEP limitation. Negative valve overlap strategy was used to keep residual gas fraction at a lower value and reduce its influence on combustion. Results shows an extended lean limit operation with ozone addition achieving higher overall efficiencies, with reduction in NOx emissions as higher the dilution of air/fuel mixture. With this, the ozone addition to enable lean combustion to appear as a potential strategy to the internal combustion engines development, reducing fuel consumption and engine-out emissions.