Influence of Laser-Induced Ignition on Spray-Guided Combustion - Experimental Results and Numerical Simulation of Ignition Processes

In this work, the potential of laser-induced ignition to improve combustion initiation and heat release in a direct-injection engine is investigated by a combined experimental and numerical investigation. Laser ignition is studied in fuel/air mixtures with homogeneous equivalence ratio fields. The results provide knowledge about minimum ignition energies and the ignition limits of laser-induced ignition. Furthermore, in mixtures with nominally identical conditions, statistical variations of the ignition success are observed experimentally. These variations can be explained, based on numerical simulations, by fluctuations in the strain rate in the turbulent in-cylinder flow. Additionally, laser ignition in engines with a spray-guided combustion mode, with strongly inhomogeneous fuel/air mixtures, was investigated. Under these conditions, reliable combustion initiation by a laser-pulse is more difficult to achieve; this is attributed to the strong mixture fraction fluctuations at the location where the laser-spark is issued.