Single-point versus multi-point laser ignition: Experimental measurements of combustion times and pressures

It has been reported that when a laser beam of irradiance on the order of 10(10) W/cm(2) interacts with a gas, a spark plasma of high temperature (on the order 10(6) K) and pressure (on the order of 10(3) atm) is generated at the end of the laser pulse. This extreme condition leads to the development of a rapidly expanding shock wave that is strong enough to ignite a gaseous combustible mixture [1-8], liquid fuel sprays [9], or even to extinguish a diffusion flame [1]. Laser ignition is nonintrusive and is capable of providing center ignition and/or multiple ignition sites that can be programmed to ignite a combustible mixture either sequentially or simultaneously [10]. Because these advantages are potentially important for fuel-lean combustion and high-speed combustion applications, the present work was designed to study laser ignition of combustible gases using three different ignition configurations: multi-point ignition, single-wall ignition, and single-center ignition. In particular, we investigated the effects of these ignition configurations on ignition and combustion properties such as combustion pressure and time for H(2)air, and CH4/air mixtures.