| 摘要: | 本研究使用實驗室一大型膠囊狀腔體，內建置一截面為正方形之流道管(Flow Tunnel)實驗平台，來探討在當量比= 0.6預混貧油甲烷/空氣燃氣之引燃機率(Ignition Probability, Pig)，使用奈秒重覆脈衝放電(Nanosecond Repetitively Pulsed Discharge, NRPD)進行引燃實驗，主要量測不同入口流速(Inlet Velocity, Uin = 2.5 m/s、5 m/s)，不同脈衝重覆頻率(Pulsed Repetitive Frequency, PRF = 0.5-20 kHz)以及不同的脈衝數(Pulse Numbers , Np = 10、20、50)，在固定不鏽鋼尖端電極間距(dgap = 2 mm)，對Pig之影響，並使用高速紋影法觀察初始火核的形成與發展行為。結果顯示，NRPD 引燃具有統計性質，即使在相同累積總能量(Etot ≈ 20.6 mJ, Np = 10）下，仍可能同時出現引燃成功(Go)與引燃失敗(No Go)案例。本研究第一個放電脈衝能量約為0.8 mJ，後續每個放電的脈衝能量約2.2 mJ。入口流速對引燃機率有重要影響，當固定Np = 10條件下，在PRF = 5 kHz-10 kHz，Uin = 5 m/s的Pig皆比在Uin = 2.5 m/s時低，說明入口流速增加，對流熱損失較強，火核成長受限，使引燃較為困難。脈衝數對引燃機率也具有重要影響，脈衝數增加，即累加總能量增加。在Uin = 5 m/s和PRF = 5kHz時，當Np = 10, 20, 50時，相對應之P = 0%, 6%, 9%。而在Uin = 5 m/s和PRF = 6-15 kHz的範圍時，不同Np的Pig值皆有上升的趨勢。在Np = 10時，需在PRF = 15 kHz才可達到Pig = 100%，Np = 20則在PRF = 10kHz就能達到Pig = 100%，Np = 50則在PRF = 8 kHz就可達到Pig = 100%，而入口流速Uin = 2.5 m/s也有類似趨勢。說明增加脈衝數，能夠在更低的PRF的條件引燃成功，可以增加引燃的穩定性。本研究量測 PRF、Np與Uin三種參數對引燃機率之影響，對於預混貧油甲烷燃氣在流動環境中之電漿輔助引燃策略具有參考價值;In the present study, a large capsule-shaped chamber equipped with a square-cross-section flow tunnel is employed to investigate the ignition probability (Pig) of a lean premixed methane/air mixture at an equivalence ratio of = 0.6 using nanosecond repetitively pulsed discharge (NRPD) ignition. Experiments are conducted to quantify the effects of inlet flow velocity (Uin = 2.5 and 5 m/s), pulse repetition frequency (PRF = 0.5–20 kHz), and pulse number (Np = 10, 20, and 50) on Pig, while the stainless steel sharp-end electrodes, gap distance is fixed at dgap = 2 mm. High-speed schlieren imaging is utilized to visualize the formation and evolution of the initial flame kernel. The experimental results reveal that NRPD ignition exhibits a statistical nature. Even using the same accumulated ignition energy (Etot ≈ 20.6 mJ at Np = 10), both successful ignition (Go) and ignition failure (No Go) events can co-exist. In the present configuration, the first discharge pulse deposited energy is approximately 0.8 mJ, while the second and subsequent pulse energies are approximately 2.2 mJ. The inlet flow velocity is found to play a role in ignition performance. At a fixed pulse number of Np = 10 and PRF = 5-10 kHz, Pig at Uin = 5 m/s is consistently lower than that at Uin = 2.5 m/s, indicating that increased convective heat losses at higher flow velocity suppress flame kernel growth and hinder ignition. The pulse number is also shown to have a significant influence on Pig through the accumulation of ignition energy. At Uin = 5 m/s and PRF = 5 kHz, Pig increases from 0% and 6% to 9% as Np increases from 10 and 20 to 50, respectively. Within the PRF range of 6–15 kHz, Pig increases for all pulse numbers. Specifically, Pig = 100% can be achieved at PRF = 15 kHz when Np = 10, at PRF = 10 kHz when Np = 20, and at PRF = 8 kHz when Np = 50. A similar trend is observed at Uin = 2.5 m/s. These results demonstrate that increasing the pulse number enables successful ignition at lower PRF values and enhances ignition stability. Overall, the present study systematically elucidates the combined effects of PRF, pulse number, and inlet flow velocity on NRPD ignition under flowing conditions. The findings provide valuable reference for the development and optimization of plasma-assisted ignition strategies for lean premixed methane combustion in practical flow environments. |
