A Study of Energy Enhanced Multi-Spark Discharge Ignition in a Constant-Volume Combustion Chamber 2019-01-0728

Multi-spark discharge (MSD) ignition is widely used in high-speed internal combustion engines such as racing cars, motorcycles and outboard motors in attempts to achieve multiple sparks during each ignition. In contrast to transistor coil ignition (TCI) system, MSD system can be greatly shortened the charging time in a very short time. However, when the engine speed becomes higher, the ignition will be faster, electrical energy stored in the ignition system will certainly become less, especially for MSD system. Once the energy released into the spark plug gap can’t be guaranteed sufficiently, ignition will become more difficult, and it will get worse in some harsh environment such as strong turbulence or lean fuel conditions. With these circumstances, the risks of misfire and partial combustion will increase, which can deteriorate the power outputs and exhaust emissions of internal combustion engine. Therefore, in order to extend the ignitability limit and reduce the combustion variation without sacrificing spark energy for high speed engines, an energy enhanced multi-spark discharge (EEMSD) ignition system is developed in this study. The principle of EEMSD system is based on the capacitor discharge, it can generate 5-15kHz high-frequency sparks. Firstly, the driver circuit design and control strategy of the proposed ignition system is described. Secondly, the characteristics of discharge current and voltage are measured and analyzed under three different working frequencies. Finally, a detailed combustion experiment is investigated comparing with traditional MSD ignition system in a constant-volume combustion chamber by using the shadowgraph method. Results show that the EEMSD system has a very short charging time comparing with TCI system, and it can release much more energy into the spark plug gap, which can format a larger volume of the spark kernel and accelerate early flame propagation.