Assessment of the impact of low-speed-pre-ignition mitigation techniques on emission levels

Low-speed-pre-ignition (LSPI) presents a great challenge for developing smaller, more efficient internal combustion engines. Current research focuses on understanding the causes of LSPI and developing strategies to mitigate its intensity or eliminate it completely. On this paper, the effect of different LSPI mitigation strategies on emission levels is evaluated. For this purpose, a 1.0 naturally aspirated port fuel injection (PFI) engine was used. The research engine suffers from LSPI phenomena under rotation speeds below 1000 rpm and high loads. Operation parameters were controlled using a fully instrumented dynamometer cell with incylinder pressure monitoring. The occurrence of LSPI was determined by using in-cylinder pressure data paired with in-cylinder light intensity using an instrumented spark plug with optical access to the combustion chamber. The emission levels of CO, CO2, NO, NO2 amd HC were measured using a real-time emission analysis stand. The results obtained indicate that under non-stochastic LSPI, NO and NO₂ emissions tend to increase drastically due to the increasing incylinder temperatures. Reducing the air/fuel ratio has a positive effect on mitigating LSPI intensity but has a negative effect on CO and HC emissions. It is also observed that intake air temperature has an important effect on the formation of CO and NO_x under heavy knocking conditions.