Control of Early Flame Kernel Growth by Multi-Wavelength Laser Pulses for Enhanced Ignition

Area of Science:

• Combustion science
• Plasma physics
• Fluid dynamics

Background:

• Laser ignition is crucial for initiating combustion.
• Plasma dynamics significantly influence flame kernel formation and growth.
• Conventional single-pulse laser ignition faces limitations in lean fuel mixtures.

Purpose of the Study:

• To investigate the impact of plasma dynamics on laser-ignited flame growth.
• To compare single-pulse and dual-pulse laser ignition methods.
• To demonstrate a novel dual-pulse scheme for controlling flame kernel formation and extending lean ignition limits.

Main Methods:

• Comparative study of single-pulse (1064 nm) and dual-pulse (266 nm UV + 1064 nm NIR) laser ignition.
• Utilizing OH* chemiluminescence for visualizing early flame kernel evolution.
• Adjusting the axial offset of dual-pulse focal points to control plasma-driven fluid dynamics.

Main Results:

• Single-pulse ignition at lean conditions shows third lobe detachment, leading to flame extinction.
• The dual-pulse method, with optimized focal point offset, suppresses third lobe formation and reduces flame stretch.
• This approach results in reduced early flame speeds, an extended lean limit, and increased combustion efficiency.

Conclusions:

• Dual-pulse laser ignition offers superior control over plasma-driven fluid dynamics compared to single-pulse ignition.
• The optimized dual-pulse scheme effectively extends the lean ignition limit for laser-initiated combustion.
• This technique enhances combustion efficiency and reduces overall laser energy requirements.