Study on self-ignition control by reactive oxidant using high-frequency harrier-discharge plasma

以油气、汽油和天然气为燃料的内燃机，其创新的燃烧系统可以提供清洁的排气排放和高的热效率，这是人们所期望的。近年来，预混合充量压缩点火（PCCI）发动机作为固定用途的动力源受到广泛的研究，因为它具有高的热效率和非常低的NOx排放的巨大潜力。然而，在天然气发动机中，甲烷具有高自燃温度，因此天然气的稳定点火需要高压缩比、进气加热、内部EGR等。除了用于提高压缩温度和压力的这些措施之外，还提出了向进气中添加丁烷、氢气、NOx和臭氧以降低点火温度。虽然这些方法对发动机性能和排放表现出积极的影响，但PCCI天然气发动机的稳定运行需要这些技术的组合， 关于我们 在一台单缸进气道混合式PCCI天然气发动机上，在进气温度为180℃的条件下，对进气中添加臭氧对PCCI天然气发动机着火和燃烧的促进作用进行了试验研究。此外，利用详细的化学动力学来阐明实现改进的原因。本研究取得的主要认识如下：1.实验结果表明，在低当量比条件下，进气中加入少量臭氧对天然气自燃有显著的促进作用。在低当量比下，通过添加臭氧改善点火导致热效率的提高和未燃烧排放物（如THC和CO）的减少。然而，这种趋势随着臭氧浓度的增加而饱和。达到饱和水平的最小臭氧浓度取决于当量比。对于高当量比，即使少量的臭氧添加也会产生类似爆震的燃烧，因此限制了发动机的最大输出功率。燃烧分析表明，添加臭氧后，着火提前，缸内最高压力和放热率提高，燃烧波动明显减小。然而，这些趋势随着臭氧浓度的增加而饱和。粗略估算表明，在本研究的实验条件下，加入100ppm的臭氧相当于进气温度升高40℃。生产这种量的臭氧需要120W的电力。2.化学动力学计算结果表明，臭氧在压缩冲程初期分解形成活性组分，是改善天然气着火和燃烧的主要原因。通过计算也证实了臭氧浓度增加对着火改善的饱和趋势。结果表明，这种趋势是由于HO_2和H_2O_2对天然气着火的影响有限所致。少

Internal combustion engines fueled by gas-oil, gasoline and natural gas have been expected with the innovative combustion systems which can provide clean exhaust emissions and high thermal efficiency. Recently, Premixed Charge Compression Ignition (PCCI) engine as a power source for stationary applications is under extensive investigation due to its great potential for high thermal efficiency and very low NOx emissions. However, in natural-gas engines, methane has a high auto-ignition temperature, therefore stable ignition of natural gas requires high compression ratio, intake air heating, internal EGR and so forth. In addition to such measures for elevating the compression temperature and pressure, addition of butane, hydrogen, NOx and ozone into intake gas are proposed to lower the ignition temperature. Although these methods exhibit positive effects on the engine performance and emissions, stable operation of PCCI natural-gas engines would require combination of these techniques and … More this demands further investigation.In this research, possibility of ignition and combustion promotion in PCCI natural gas engine with intake ozone addition was experimentally investigated using a single cylinder port mixing natural gas PCCI engine when intake gas temperature was kept constant at 180℃. In addition, detail chemical kinetics was utilized to clarify the reason for achieved improvements. Followings are main understanding obtained in this study.1. The experimental results indicate that small amount intake addition of ozone greatly promotes the auto ignition of natural gas typically under the low equivalence ratios. And under low equivalence ratios, ignition improvement by ozone addition results in improvements in thermal efficiency and reduction of unburned emissions such as THC and CO. However, this trend saturates with increase in the ozone concentration. Minimum ozone concentration to reach the saturation level depends on the equivalence ratio. For high equivalence ratios, even small ozone addition gives knock like combustion and therefore limits the maximum engine output power. Combustion analysis shows that ozone addition advances the ignition timing, increase the maximum in-cylinder pressure and heat release rate and greatly lowers the combustion fluctuation. However, these trends saturates with the increase in the ozone concentration. Rough estimation indicates that under experimental condition, of this study, addition of 100ppm of ozone corresponds to 40℃ increase in the intake gas temperature. Production of this amount of ozone requires electric power of 120W.2. Chemical kinetic calculation results show that decomposition of ozone at the early stages of the compression stroke forms active species, which are mainly responsible for improvement in the ignition and combustion of natural gas. Saturation trend in ignition improvements by increase in ozone concentration was also confirmed by the calculation. The results show that this trend is due to limited effects of HO_2 and H_2O_2 on the natural gas ignition. Less