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The effect of spark-plug heat dispersal range and exhaust valve opening timing on cold-start emissions and cycle-to-cycle variability
ISSN: 0148-7191, e-ISSN: 2688-3627
Published July 21, 2021 by SAE International in United States
The partnership for advancing combustion engines (PACE) is a US Department of Energy consortium involving multiple national laboratories and includes a goal of addressing key efficiency and emission barriers in light-duty engines. A major pillar of the initiative is the generation of detailed experimental data and modeling capabilities to understand and predict cold-start behavior. Cold-start, as defined by the time between first engine crank and three-way catalyst light-off, is responsible for a large percentage of NOx, unburned hydrocarbon and particulate matter emissions in light-duty engines. Minimizing emissions during cold-start is a trade-off between achieving faster light-off of the three-way catalyst and engine out emissions during that period. In this study, gaseous and soot emissions were measured at a distance representative of the three-way catalyst position downstream of the engine at a 2bar NIMEP steady-state operating condition representative of cold-start. Test matrix included sweeps of spark timing 15 degrees-before to 10 degrees-after top dead center firing (TDCf) across three different spark-plug heat dispersal ranges. Additionally, the effect of varying exhaust valve opening timing on combustion stability and emissions was also studied. Results show that the spark plug heat dispersal range affects cycle-to-cycle variation (COV) under all cold-start conditions, while impact on emissions was found to be minimal. Furthermore, at very retarded spark timings, colder spark plugs required significantly higher air and fuel flows to maintain the desired 2bar NIMEP load, however the fraction of fuel energy going into the exhaust was found to be similar for all spark plugs. Retarding exhaust valve timings showed a simultaneous reduction in emissions while increasing the fraction of fuel energy being fed into the exhaust. However, engine COV was also observed to increase with retarded exhaust timings.