汽油机倒拖条件下纳秒重复脉冲放电特性的可视化研究

Visualization Study of Nanosecond Repetitively Pulsed Discharge Characteristics in a Motored Gasoline Engine

在倒拖的单缸光学发动机上,利用高压纳秒脉冲点火系统,研究了不同转速、放电起始时刻和脉宽下的连续高压脉冲放电特性.结果表明:与发动机停机时大气压力下的放电相比,在发动机倒拖运转时,火花塞电极击穿后的电压有上升的趋势,而且击穿电压和累计放电能量大幅升高,放电区域尺寸和亮度明显大于停机时;在任一转速下,第1个放电脉冲所对应的击穿电压和放电能量远高于后续放电脉冲,第1个放电能量占累计放电能量的(62.7±4)%;转速从1000r/min升高到2000r/min时,第1次击穿电压和累计放电能量降低;在2000r/min,循环进气量为0.4 g时,将点火时刻从25°CA BTDC推迟到5°CA BTDC,第1个高压放电脉冲的击穿电压和放电能量均升高,约化场强降低;在相同条件下,脉冲重复频率越低,连续纳秒脉冲间的耦合作用越小,第1次放电的击穿电压和累计放电能量均增加.

The characteristics of nanosecond repetitively pulsed discharge of high voltage in a burst were investi-gated in a motored single cylinder optical engine at different speed,initial discharge timing and pulse duration.The results show that,compared with the discharge at atmospheric pressure when the engine stops working,the voltage across the spark plug electrodes after breakdown tends to rise,and the breakdown voltage and cumulative discharge energy in a burst increase significantly.In the meantime,the size and brightness of the discharge area are larger.Regardless of speed,the breakdown voltage and deposited energy in the first discharge pulse are much higher,and the first deposited energy accounts for(62.7±4)%of the cumulative discharge energy in a burst.The first breakdown voltage and cumulative discharge energy decrease as speed increases from 1000r/min to 2000r/min.In the case of 0.4g per cycle at 2000 r/min,the breakdown voltage and deposited energy in the first discharge pulse increase,as the discharge timing is delayed from 25°CA BTDC to 5°CA BTDC,while the reduced field strength decreases.Under the same conditions,the coupling effect between two sequential nanosecond pulses decreases,and the first breakdown voltage and the cumulative deposited energy in a burst increase in the case of low pulse repetition frequency.