The present study investigates the potential impact of spark-assisted (SA) homogeneous charge compression ignition (HCCI) on pollutant exhaust gas emissions from an internal combustion engine. A single-cylinder research engine was used to compare the exhaust emissions of the engine when operated in HCCI, SA-HCCI and conventional spark ignited modes of operation. The study builds on previous results demonstrating the effects of the spark plasma kernel on the ignition process [1, 2]. Specifically, this study investigates the NOx, CO, and HC emissions from an optical engine fueled with indolene in HCCI and SA-HCCI modes at fuel lean conditions. Fuel/air equivalence ratios ranged from φ = 0.3–0.6. Time-averaged emissions were measured using an exhaust gas analyzer. In-cylinder pressure data were also acquired. The results show NOx emissions follow the trends of peak in-cylinder pressure implying that thermal NOx mechanisms dominate both the HCCI and SA-HCCI modes of engine operation. For SA-HCCI, spark timing could be used to change ignition phasing, and consequently change the in-cylinder peak pressure and resulting NOx emissions. Comparing HCCI and SA-HCCI emissions at nominally similar conditions (specifically, comparable indicated mean effective pressures and equivalence ratios) yielded similar NOx emissions. These data show that SA-HCCI may not have a NOx penalty when the spark timing is carefully applied.

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