Comparison of laser breakdown and laser ablation ignition thresholds of combustible gas mixtures

Abstract

One of the strong advantages stated for laser spark plugs is the ability to ignite fuel lean mixtures resulting in improved fuel economy and reduced NO x emission. However, lean mixtures demand high laser pulse energies for ignition. That could be overcome by using laser ablation rather than optical breakdown plasma to establish the combustion core. For fuel equivalence ratios ϕ ≈ 0.4–1.3, we have experimentally compared ignition thresholds for these two cases at pressures of p ≈ 1–3 bar of a butane-based combustible mixture. Our results show that laser pulse energy for fuel lean mixtures ignition can be significantly (by more than an order of magnitude) reduced using the ablator (stainless steel SS304) as compared to optical breakdown.