In this work, the two-photon laser-induced fluorescence technique (TPLIF) was applied to measure the concentration profile of atomic hydrogen in low-pressure laminar premixed flames. Excitation of H-atoms was performed by two-photon absorption at 205 nm and collecting the fluorescence at 656.3 nm. For the first time in flames, the TPLIF signals from the H-atom have been calibrated using the TPLIF signal from krypton, directly seeded in the flame, excited at 204.13 nm and collecting the fluorescence at 826.5 nm. This method was previously demonstrated in plasma environments and recently applied in our group to calibrate O-atom TPLIF signals using xenon as a standard gas. The calibration requires the measurements of TPLIF signals of H and Kr atoms in a flame, where the quenching rates can be determined from time-resolved LIF measurements. Given the short fluorescence lifetime of H-atom, this last task was particularly challenging. A calibration flame was chosen to minimize collisions and the response time of the detection was determined using a deconvolution method. We found that the quenching rate is fairly constant around 4.6 × 10⁸ s⁻¹ at 5.3 kPa in a large portion of the flame. The calculated quenching rate overestimates the measured value from 35% to 500% depending on the chosen assumption on the dependence of the quenching coefficient with temperature. The quantitative measurement of H-atom mole fraction was carried out in three nitrogen-diluted low-pressure methane flames. The experimental profiles were compared with the calculated ones using chemical modeling. The variation in the experimental H-atom mole fraction in the range of equivalence ratios agrees well with the simulated values. Quantitatively, the calculated mole fractions agree within 30% with the experimental ones. The method is robust but its accuracy is limited by the uncertainty in the knowledge of the ratio of the two-photon cross-sections of Kr and H atoms. Application of this calibration method to atmospheric is discussed.

在这项工作中，采用了双光子激光诱导荧光技术（TPLIF）来测量低压层流预混火焰中原子氢的浓度分布。通过在205 nm处吸收两个光子并在656.3 nm处收集荧光来激发H原子。火焰中的H原子的TPLIF信号已首次使用using的TPLIF信号进行了校准，该信号直接植入火焰中，在204.13 nm处激发，并在826.5 nm处收集荧光。该方法先前在等离子体环境中得到证明，最近在我们的研究组中应用，以氙作为标准气体校准O原子TPLIF信号。校准需要测量火焰中H和Kr原子的TPLIF信号，其中猝灭速率可以通过时间分辨LIF测量来确定。鉴于H原子的荧光寿命短，这最后一项任务特别具有挑战性。选择校准火焰以最大程度地减少碰撞，并使用解卷积方法确定检测的响应时间。我们发现淬火速率在4.6×10左右相当恒定⁸ 秒^-1在大部分火焰中为5.3 kPa。根据选择的淬灭系数与温度的关系假设，计算出的淬灭率会将测量值高估35％至500％。H原子摩尔分数的定量测量是在三个氮气稀释的低压甲烷火焰中进行的。使用化学模型将实验曲线与计算曲线进行比较。在当量比范围内，实验氢原子摩尔分数的变化与模拟值非常吻合。从数量上讲，计算出的摩尔分数与实验值相吻合在30％以内。该方法是鲁棒的，但是其准确性受到Kr和H原子的两个光子截面之比的知识的不确定性的限制。