Dumitrache Ciprian, Butte Carter, Yalin Azer
Plasma and Radiation Physics, Solid-State Quantum Electronics Lab., National Institute for Laser, 077125, Bucharest, Romania.
Department of Mechanical Engineering, Colorado State University, Fort Collins, 80525, USA.
Sci Rep. 2020 Nov 16;10(1):19916. doi: 10.1038/s41598-020-76968-5.
This contribution investigates a novel laser ignition method based on a dual-pulse resonant pre-ionization scheme. The first laser pulse efficiently creates initial gas ionization (seed electrons) through a 2 + 1 resonantly-enhanced multiphoton ionization (REMPI) scheme targeting molecular oxygen (λ ~ 287.6 nm). This pulse is followed by a second non-resonant near-infrared pulse (λ = 1064 nm) for energy addition into the gas via inverse bremsstrahlung absorption. The sequence of two pulses creates a laser induced plasma that exhibits high peak electron number density and temperature (n ~ 8 × 10 cm at t = 100 ns and T ~ 8000 K at t = 10 μs, respectively). These plasma parameters are similar to those attained for typical single-pulse near-infrared laser plasmas but with the advantage of substantially lower pulse energy (by factor of ~ 2.5) in the dual-pulse REMPI case. A combustion study focusing on ignition of propane/air mixtures shows that the dual-pulse REMPI method leads to an extension of the lean flammability limit, and an increase in combustion efficiency near the lean limit, as compared to laser ignition with a single NIR pulse. The measurement results and observed gas dynamics are discussed in the context of their impact on combustion applications.
本文研究了一种基于双脉冲共振预电离方案的新型激光点火方法。第一个激光脉冲通过针对分子氧（波长λ287.6nm）的2+1共振增强多光子电离（REMPI）方案有效地产生初始气体电离（种子电子）。该脉冲之后是第二个非共振近红外脉冲（λ=1064nm），用于通过逆轫致辐射吸收向气体中添加能量。两个脉冲的序列产生了一个激光诱导等离子体，该等离子体分别在t = 100ns时表现出高峰值电子数密度（n8×10cm）和在t = 10μs时表现出高温（T~8000K）。这些等离子体参数与典型的单脉冲近红外激光等离子体所达到的参数相似，但在双脉冲REMPI情况下具有脉冲能量显著更低（约为2.5倍）的优势。一项针对丙烷/空气混合物点火的燃烧研究表明，与单近红外脉冲激光点火相比，双脉冲REMPI方法导致贫燃极限的扩展，以及在贫燃极限附近燃烧效率的提高。在它们对燃烧应用的影响的背景下讨论了测量结果和观察到的气体动力学。
