Downsizing, turbocharging, and lean burn strategies offer improved fuel efficiency and engine-out emissions to that of conventional spark ignition engines. However, maintaining engine stability becomes difficult, especially at low load and low speed operation such as cold start conditions. Under cold start operation, the spark timing is retarded to rush catalyst warm-up temperature followed by advancing the spark timing for engine stability. In this sequence, securing ignition while using retarded spark timing is difficult because of the cold cylinder walls and low engine loads. Through previous investigations, the noval multiple ignition sites strategy demonstrated its capability to expend lean burn boundaries beyond traditional single core spark plug and improve cycle to cycle variation. In this work, multisite ignition is tested on a production 4-cylinder direct injection spark ignition engine.
A large number of tests are performed on the engine to investigate the impact of ignition strategy on emissions and stability during catalytic converter warm up period as part of the cold-start operation. Results show that the three-core spark igniter shortens the ignition delay thus providing a wider stable spark timing window for stable engine operation. As a result, the concentration of unburnt fuel in the exhaust gas can be reduced before the catalyst reaches the light-off temperature.