Laser-induced ignition and detonation in air-fuel mixtures

The ignition system has always posed problems in commercial applications. Many experimental, theoretical and numerical studies have been performed for the past years, and various ignition systems (e.g., electric discharge, microwave discharge, laser radiation) have been tested. Extensive efforts have been applied to circumvent several challenging engineering problems associated with the development of ignition system. These include fuel injection and mixing, repetitive detonation initiation, integration of detonation tubes with inlets and nozzles, and overall system optimization.

Laser ignition has the potential to replace the conventional electric spark plugs in internal combustion engines and other devices that will be required to operate under much higher compression ratios, faster compression rates and much leaner fuel-to-air ratios than the engines today. Laser ignition could be used to improve engine performance and ignition system durability to the required level. Compared to conventional spark ignition, laser ignition allows a more flexible choice of the ignition location inside the combustion chamber.

The injection of metal particles with low evaporation temperature and ionization potential or liquid droplets causes optical breakdown on individual particle or droplet, and leads to drop of ignition/detonation minimum pulse energy of the mixture. Some fundamental and practical problems are yet to be resolved. They include qualitative and quantitative description of processes around individual particle and droplet, knowledge in particle microphysics and optical properties of particles, sub-models of heating and evaporation, transport of aggregates of complex morphology, threshold values of optical breakdown, dependence of minimum pulse energy on the contributing factors (laser pulse, composition of gas mixture, shape of particles).

The physical and mathematical models and up-to-date numerical methodology for computer modelling will be developed and validated. Laser-induced ignition/combustion/detonation in particulate systems will be studied, and possibilities of the new methodology will be demonstrated.