Pre-chamber combustion has been applied as a method of low fuel consumption in spark ignition engines, and in recent years the application of pre-chambers to gasoline engines has also been actively studied. In many gasoline engines, stoichiometric combustion is common. We decided that a passive type pre-chamber with only one port fuel injection is sufficient for stoichiometric combustion. The pre-chamber system relatively has two merits of lower cost and ease of installing than other prechamber systems. Therefore, we focused on investigating the effects of improving combustion speed and knock resistance in use of the passive type pre-chamber and the applicability of the pre-chamber system in various operating points. As the concrete approach, we evaluated the heat balance and the knock resistance with and without a pre-chamber in engine bench test. As a result, the knock resistance and the fuel consumption were improved. In addition, as a result of considering lean burn in the passive type pre-chamber in order to further improve fuel consumption in the future, the fuel consumption in use of the passive type pre-chamber was also improved compared to that in case of no pre-chamber. Furthermore, as a result of evaluating the combustion characteristics of the pre-chamber due to differences in operating points depending on the combination of engine revolution and engine load, it was found that while sufficient rapid combustion was obtained even at high engine revolution, combustion became unstable at extremely low load. Moreover, under high load, pre-ignition could occur in the pre-chamber over time. We analyzed these mechanisms and discussed countermeasures.
