Browse Publications Technical Papers 2019-01-2151
2019-12-19

Investigation on Knock Resistance with Turbulent Jet Ignition at Different Engine Load in an Optical Engine 2019-01-2151

This research was focused on the effect of pre-chamber ignition and compared the knock limit of normal spark ignition in the main chamber and pre-chamber jet ignition combustion in a spark ignition gasoline engine. Experiments were conducted in a single-cylinder engine with optical access. Engine was operated with stoichiometric air/fuel mixtures at 1200 rev/min and different inlet pressures of 1, 1.2, and 1.4 bar. No auxiliary fuel was injected into the pre-chamber when jet-ignition mode was used. The results show that significant knock limit extension can be realized with use of a pre-chamber ignition unit. The main differences in engine performance, heat release and combustion, knock resistance and flame propagation were compared between the pre-chamber ignition and conventional spark ignition in the main chamber by in-cylinder pressure measurements and high-speed flame chemiluminescence imaging.
Pre-chamber ignition is capable of extending the knock limit over conventional spark ignition combustion due to the burn rate enhancement. Pre-chamber ignition lowered the CoV of IMEP. For instance, at inlet pressure 1.2 bar and common spark timing 18 °CA bTDC, CoV of IMEP with pre-chamber ignition was only around 2%, whereas normal SI reached almost 4.5%. At inlet pressure 1.0 bar, IMEP is lower with jet ignition comparing with normal SI but at elevated inlet pressures of 1.2 bar and 1.4bar pre-chamber ignition always produces higher IMEPs. The knock intensity increased as the inlet air pressure increased and spark timing advanced. The high speed combustion images show that incomplete combustion of ignition jets was present during the knocking combustion cycle.

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