Resonant dual-pulse laser ignition technique based on oxygen REMPI pre-ionization

Area of Science:

• * Combustion science
• * Laser-induced plasma physics
• * Chemical engineering

Background:

• * Laser ignition is a promising alternative to conventional ignition methods.
• * Achieving efficient laser-induced plasma requires careful control of laser parameters and gas conditions.
• * Optimizing laser ignition for lean fuel mixtures is crucial for improving combustion efficiency and reducing emissions.

Purpose of the Study:

• * To investigate a novel dual-pulse laser ignition method.
• * To characterize the plasma generated by the dual-pulse scheme.
• * To evaluate the impact of this method on the ignition and combustion of propane/air mixtures.

Main Methods:

• * A dual-pulse laser system was employed, combining 2+1 resonantly-enhanced multiphoton ionization (REMPI) of O2 at 287.6 nm and a 1064 nm near-infrared pulse.
• * Laser-induced plasma parameters (electron density and temperature) were measured.
• * Ignition and combustion of propane/air mixtures were studied using the dual-pulse laser ignition method and compared to single-pulse ignition.

Main Results:

• * The dual-pulse REMPI scheme generated plasma with high electron density (~8x10^17 cm^-3) and temperature (~8000 K) at significantly lower pulse energy (2.5x lower) than single-pulse methods.
• * The dual-pulse laser ignition extended the lean flammability limit of propane/air mixtures.
• * Combustion efficiency near the lean limit was enhanced compared to single-pulse laser ignition.

Conclusions:

• * The dual-pulse resonant pre-ionization laser ignition method is an effective technique for initiating combustion.
• * This method offers advantages in terms of energy efficiency and improved combustion performance, particularly for lean mixtures.
• * The findings have significant implications for advanced combustion applications and engine design.