Multi-Cylinder Laser and Spark Ignition in an IC Gasoline Automotive Engine: A Comparative Study

A direct comparison of engine performance and stability is made between two different systems for igniting gasoline and air mixtures in an internal combustion (IC) engine. A conventional spark ignition (SI) coil and electrical plug setup is compared to a laser ignition (LI) system, comprising of two Q-switched Nd:YAG lasers and a series of mirrors and lenses. The lasers were operated in single-mode at the fundamental wavelength of 1064 nm and were successfully used to ignite air-fuel mixtures in all four cylinders from engine start-up without misfires. The test engine used was an unmodified four cylinder 1.6 litre port fuel injection (PFI) production engine. Both ignition systems were triggered twice per engine cycle with one redundant spark on the exhaust stroke and the second spark on the compression stroke to ignite the air-fuel mixture.

The results are presented in terms of changes in coefficient of variation in indicated mean effective pressure (COV_IMEP) and the variance in the peak cylinder pressure position (Var_PPP), measured for each engine cylinder. Laser induced ignition was demonstrated to improve the combustion stability, shown through a reduction in COV_IMEP and Var_PPP for a range of engine speeds (800 - 2400 rpm), loads (50 - 75 Nm) and ignition timings (16 - 36° before top dead centre), when compared to conventional electrical spark plugs.