Effects of Pre-chamber Enrichment on Lean Burn Pre-chamber Spark Ignition Combustion with a Narrow-throat Geometry 2020-01-0825
Pre-chamber spark ignition (PCSI) combustion is an emerging lean-burn combustion mode capable of extending the lean operation limit of an engine. The favorable characteristic of short combustion duration at the lean condition of PCSI results in high indicated efficiencies and low specific fuel consumption compared to conventional spark ignition combustion. Since the engine operation is typically lean, PCSI can significantly reduce engine-out NOx emissions while maintaining relatively short combustion duration. In this study, experiments were conducted on a heavy-duty engine at mid to low loads to study the effects of pre-chamber enrichment on globally lean combustion with methane fuel injection in both pre and main chambers. Two parametric variations were performed where, in the first study, the total fuel energy input to the engine was fixed while the intake pressure was varied, which resulted in varying the global air excess ratio. In the second, the intake pressure was fixed while the amount of fuel injection was changed to alter the global air excess ratio. At each global air excess ratio, the fuel injection to the pre-chamber was varied parametrically to assess the effect of pre-chamber enrichment on engine operating characteristics. Multi-chamber heat release analysis was performed in order to investigate the pre-chamber and main chamber heat release characteristics separately. The discharge coefficient of the pre-chamber nozzles was estimated by the model calibration using a 1-D GT Power Model. The analyzed data revealed two-stage combustion in the main chamber where the second stage is thought to be indicating auto-ignition of the main chamber charge. As the global air excess ratio became leaner, the combustion efficiency deteriorates as the emissions of HC and CO increased while NOx emission declined significantly. The resulting heat release data is presented alongside the engine-out specific emissions.
Ponnya Hlaing, Manuel Echeverri Marquez, Eshan Singh, Fahad Almatrafi, Emre Cenker, Moez Ben Houidi, Bengt Johansson
King Abdullah University of Science & Technology, Saudi Aramco