Ignition breakdown kernels of methane-air mixtures initiated by laser- induced sparks and by conventional electric sparks are compared during initial stages. Experiments were conducted using a four-stroke (Otto-cycle) single-cylinder typical high-pressure combustion chamber. The piston is cycled in the cylinder by using an electric motor driven hydraulic ram. An excimer laser beam, either produced from krypton fluoride gas (λ = 248 nm) or argon fluoride gas (λ = 193 nm), or a Nd:YAG laser beam (λ = 1064 nm) is focused into a combustion chamber to initiate ignition. Conventional electric spark ignition is used as a basis for comparison between the two different ignition methods and the resultant early breakdown kernel characteristics. A streak camera is used to investigate and record the initial stages of kernel formation. Both a breakdown and a radial expansion wave of the ignition plasma are observed for certain laser ignition conditions of methane-air mixtures under typical internal combustion (IC) engine conditions. Results indicate that only certain wavelengths used for producing laser ignition produce a radial expansion wave. Laser ignition kernel size is calculated and laser-supported breakdown velocity is calculated by using Raizer's theory and is compared with measured results. Laser ignition results in a 4-6 ms decrease in the time for combustion to reach peak pressure than is obtained when using electric spark ignition in the same combustion chamber and under the same ignition conditions.
ASJC Scopus subject areas
- Chemical Engineering(all)
- Fuel Technology
- Energy Engineering and Power Technology
- Physics and Astronomy(all)