An experiment on the combustion characteristics with laser-induced spark ignition

The combustion characteristics and minimum ignition energies using laser-in duced spark ignition were demonstrated for quiescent methane-air mixtures i n an optically-accessible, constant volume combustion chamber. Initial pres sure and equivalence ratio as well as spark energy were varied in order to explore the flame behavior with laser-induced spark ignition. Shadowgraphs for the early stages of combustion process showed that the flame kernel bec omes separated into two, one of which grows back towards the laser source. Eventually after a short period, the two flame kernels developed into two f lame fronts propagating individually, which is unique in laser-induced spar k ignition. For a given mixture, lower initial mixture pressure and higher spark energy resulted in shorter flame initiation period and faster flame p ropagation. The results of minimum ignition energies for laser ignition sho ws higher values than electric discharge results, however, the difference d ecreases toward lean and rich flammability limits.