Abstract
Low emission gases and good fuel economy are obtainable with very lean mixture combustion. However. unsta- ble operation caused by misfire and erratic combustion prevents spark ignition engines from being operated in the very lean condition. It is well known that such abnor- mal combustion originates during the initial stages of combustion from the time of the breakdown phase.
These cyclic variations might be reduced, chemically, by increasing the laminar burning velocity, for instance by using rich mixture or by reducing the exhaust residual mass fraction or by changing the fuel. However, in practice these options do not really exist for reasons of fuel economy and acceptable exhaust emissions; moreover engines have to use normally acceptable fuels.
The other well established way of improving this early phase of combustion is through the ignition process, for instance by increasing the energy of the conventional spark.
Therefore, a study has been undertaken with a specially designed inductive coil ignition system to determine whether the higher ignition energy is beneficial in stabilizing the engine operating condition near the Lean Misfire Limit (LML) and extending the Lean Misfire Limit. The result of the study is that the higher ignition energy improves the engine stability and fuel consumption rate, and reduces BSHC.