Spark and laser ignition of iso-octane and ethanol blends

Laser ignition is being considered as a possible replacement for spark plugs in combustion engines due to its ability to ignite lean mixtures. Despite the trend of increasingly fuel-flexible engines, research in this area has mainly focused on methane combustion. As our understanding of the fundamentals of laser ignition improves, we must begin to focus on the behavior of candidate fuels. In this study we compare laser and conventional spark ignition of iso-octane and blends including ethanol. Laser ignition is performed using an Nd:YAG laser emitting at 532 nm. Experiments are carried out in a cylindrical stainless steel vessel, equipped with 6 optical access points. Visualization of the ignition process is performed using Schlieren imaging. Flame kernel behavior for both spark and laser ignition is studied at varying equivalence ratios, up to the lean flammability limit. Further, minimum ignition energies are determined for laser ignition. This study investigates possible performance benefits of laser ignition in gasoline and ethanol fueled engines.