Dilution is a promising way to improve fuel economy of Spark-Ignited (SI) gasoline engines. In this context, influence of innovative ignition systems on the dilution acceptance of a 400cc optical GDI engine has been studied. Several systems were tested and compared to a conventional coil: a dual-coil system and two nanosecond scaled plasma generators. Two operating points were studied: 2.8bar IMEP (net) at 2000rpm and 9bar IMEP (net) at 1200rpm. Two diluents were evaluated: real EGR and air (lean combustion). High-speed imaging at frequency up to 10kHz was performed to visualize both spark and combustion initiation and propagation. Voltage and current were measured to infer the energy deposited in the spark plug gap.
The dual-coil DCO™ system and the nanosecond multi-pulse plasma generator at their maximum power showed an ability to extend the dilution range of the engine. The flexibility of these devices allowed to conduct studies to evaluate the influence of parameters such as spark duration, spark energy profile deposition. Results show that the dilution limit can be pushed back in certain conditions. Significant gain in the dilution tolerance is obtained by increasing the energy deposition at lower load conditions (2.8bar * 2000rpm), whereas no influence of the ignition system is observed at higher load conditions (9bar * 1200rpm). At low load conditions, it is demonstrated that energy deposition appears to be the key ignition parameter to extend engine stable operation range through higher dilution rate, spark duration showing no significant influence.
