Fuel concentration information is critical to the development of high-efficiency combustion system of direct-injection natural gas engines. In this study, a one-dimensional (1-D) measurement approach based on laser induced breakdown spectroscopy (LIBS) is developed to quantitatively measure 1-D fuel concentration distributions in gas jets at high ambient pressures. Except for the spectral dimension, another dimension of the intensified charge coupled device (ICCD) is employed for the spatial resolution of measurements. The effects of laser energy and ambient pressure on plasma dynamics are investigated to explore the feasibility of 1-D LIBS in concentration measurements at high ambient pressure. Since the peak intensity ratio (PIR) of H656/N746 shows significant spatial variations in the plasma volume, a 1-D calibration strategy is developed by establishing respective calibration curves at different spatial positions to quantify the fuel concentration distributions. The measurement uncertainties are evaluated, including both the systematic and random errors. The temporal variations of the 1-D fuel concentration distributions in methane jets are presented, and the shot-to-shot fluctuations are analyzed in detail. The results show that the coefficient of variation of equivalence ratio is lowest at the end of injection (EOI), suggesting that ignition at the EOI could enable a relatively stable flame kernel formation. Along the radial direction of the jet, a high ignitable mixture percentage appears at approximately 3.0 mm from the jet axis at the EOI, suggesting an optimal ignition position. The results reveal that the 1-D LIBS could be a powerful tool for calibration of numerical models and optimal designs of combustion engines taking advantage of high-pressure gas jets.

燃料浓度信息对于开发直喷式天然气发动机的高效燃烧系统至关重要。在这项研究中，开发了一种基于激光诱导击穿光谱法（LIBS）的一维（1-D）测量方法，以定量测量在高环境压力下气体喷射器中的一维燃料浓度分布。除频谱尺寸外，增强型电荷耦合器件（ICCD）的另一尺寸用于测量的空间分辨率。研究了激光能量和环境压力对等离子体动力学的影响，以探索一维LIBS在高环境压力下进行浓度测量的可行性。由于H656 / N746的峰强度比（PIR）在血浆体积中显示出明显的空间变化，通过在不同的空间位置建立相应的校准曲线来量化燃料浓度分布，从而开发出一维校准策略。评估测量不确定度，包括系统误差和随机误差。给出了甲烷喷口中一维燃料浓度分布的时间变化，并详细分析了喷射之间的波动。结果表明，当量比的变化系数在喷射结束时（EOI）最低，这表明在EOI点火可以实现相对稳定的火焰核形成。沿射流的径向方向，在EOI处距射流轴约3.0 mm处出现高可燃混合物百分比，表明存在最佳点火位置。