Effects of laser parameters on laser ignition in an internal combustion engine

Recent research in laser-induced ignition (LI) of air-fuel mixtures in internal combustion (IC) engines has shown there to be many potential advantages over conventional electrical spark ignition (SI). Spark plugs offer only limited possibilities for optimising engine efficiency, due to their fixed position within a cylinder and the protrusion of electrodes which disturb the cylinder geometry and can quench the flame kernel. Laser radiation is non-invasive and has greater flexibility in terms of the ignition position, allowing the possibility of multipoint ignition. Other potential benefits of LI include: reduced emissions, more stable combustion and lower idle speeds, when compared to conventional SI. This paper reports on the current research being undertaken at The University of Liverpool, which examines the effects of engine combustion performance and stability when specific laser parameters (beam energy, minimum spot size and focal length/volume) are varied. A Q-switched Nd:YAG laser operating at the fundamental wavelength 1064 nm was used to ignite gasoline and air mixtures in one cylinder of a 1.6 litre IC engine, where the remaining three cylinders used conventional SI. A direct comparison between LI and conventional SI is presented in terms of changes in coefficient of variability (COV) in indicated mean effective pressure (IMEP) and the variance in the peak cylinder pressure position (PPP).