Abstract This study focuses on the laser energy deposition characteristics through single and double pulse at short and long pulse intervals in quiescent air, both experimentally and numerically. A frequency-doubled and Q-switched Nd: YAG laser is used to create the spark in the air. High-speed schlieren imaging technique is used to visualize the shock-wave evolution and plasma kernel expansion. To estimate the energy available for ignition, the energy absorbed is measured and the energy loss through the shock-wave is estimated by using Jones blast wave model. Two-dimensional numerical simulations are carried out by solving the Navier-Stokes equations along with the species conservation equations in finite volume framework. After cessation of the laser pulse, the breakdown zone assumed to consists of seven species (O2, O, N2, N, NO, NO+ and e − ). For double pulse at short pulse interval, the second pulse absorbed more energy than the first pulse, and the shock loss is relatively higher. The lifetime of plasma is found to have increased by 13.56 % due to the jump in temperature and pressure after the introduction of the second pulse. Same total energy two successive laser pulses at short time interval are found to be a promising alternative of single pulse for lean limit of combustion. The amount of energy left in the kernel for ignition is 16.02 % and 15.78 % of the absorbed energy in 50 + 50 mJ and 100 + 100 mJ double pulse respectively. In case of double laser pulse deposition at long pulse interval, along with multiple layers of shock-wave, a third lobe and a fourth lobe are observed on either side (upstream and downstream) of the plasma kernel enhancing the kernel surface area and mixing process.

中文翻译：

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双脉冲激光能量在空气中沉积的实验和数值研究

摘要 本研究的重点是在静止空气中通过短脉冲和长脉冲间隔的单脉冲和双脉冲激光能量沉积特性，通过实验和数值进行研究。倍频和调Q Nd: YAG 激光器用于在空气中产生火花。高速纹影成像技术用于可视化冲击波演化和等离子体核膨胀。为了估计可用于点火的能量，测量吸收的能量，并使用琼斯冲击波模型估计通过冲击波的能量损失。二维数值模拟是通过求解 Navier-Stokes 方程以及有限体积框架中的物种守恒方程来进行的。激光脉冲停止后，击穿区假定由七种物质（O2、O、N2、N、NO、NO+ 和 e - ）组成。对于短脉冲间隔的双脉冲，第二个脉冲比第一个脉冲吸收更多的能量，冲击损失相对较高。由于引入第二个脉冲后温度和压力的跳跃，等离子体的寿命增加了 13.56%。发现在短时间间隔内两个连续激光脉冲的总能量相同是单脉冲的有前途的替代方案，用于稀薄燃烧极限。在 50 + 50 mJ 和 100 + 100 mJ 双脉冲中，留在内核中用于点火的能量分别为吸收能量的 16.02% 和 15.78%。在长脉冲间隔的双激光脉冲沉积的情况下，伴随着多层冲击波，