Fundamentals of high-energy spark ignition with lasers

Laser Ignition of Iso-Octane Air Aerosols

“…6. Also shown is the shockwave radius for a gas phase ignition, (E = 224 mJ, for the same ignition system, from Bradley et al (2004)) which is consistently larger than those measured here. The energies deposited in sites 4 and 5 was calculated to be 65 and 9 mJ respectively; thus over 7 times more energy was deposited within the larger ignition kernel.…”

“…6 for a number of shock fronts. Although laser ignition does not provide instantaneous energy input, and the initial plasma volume is finite, blast wave analysis is often applied to gas phase laser ignition with reasonable agreement (Spiglanin et al 1995 andBradley et al, 2004). In the present work the estimated energy deposited in each ignition site, E, was found from measurements of the shock wave radius, r s ,.…”

“…3 can be seen to be poor. This was probably due to the nature of the energy deposition which was not instantaneous but was finite (Bradley et al, 2004). …”

“…A x4 beam expander (Gallilean telescope) was employed to enlarge the beam to enable a tighter focus and a plano convex lens focused the beam at the centre of the vessel. The same system was used in a previous study on gas phase laser ignition (Bradley et al, 2004) Explosion vessel and aerosol characteristics Aerosol mixtures were generated in a combustion bomb by the Wilson cloud chamber technique (Wilson, 1911). This technique has been used previously in combustion studies by Hayashi (1976) and Lawes et al (2006).…”

“…Laser intensities of the order of 200 GW/cm 2 for air at 100 kPa and 300 K are required to generate a plasma in a gas (Bradley et al, 2004). The plasma is formed via the relatively inefficient process of multiphoton ionisation and inverse bremsstrahlung resulting in an electron cascade and then a plasma (Radziemski, 1989).…”