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

以天然气、石油、汽油和天然气为燃料的内燃机已经被期望具有创新的燃烧系统，可以提供清洁的废气排放和高热效率。近年来，预混装药压缩点火（PCCI）发动机由于具有高热效率和极低氮氧化物排放的巨大潜力，作为固定式应用的动力源正受到广泛的研究。而在天然气发动机中，甲烷的自燃温度较高，因此天然气的稳定点火需要高压缩比、进气加热、内部EGR等。除了提高压缩温度和压力外，还提出了在进气中添加丁烷、氢气、NOx和臭氧来降低点火温度的措施。虽然这些方法对发动机的性能和排放都有积极的影响，但PCCI天然气发动机的稳定运行需要这些技术的结合，这需要进一步的研究。在进气温度为180℃的条件下，利用单缸进气口混合天然气PCCI发动机，对进气添加臭氧后PCCI天然气发动机点火助燃的可能性进行了实验研究。此外，利用详细的化学动力学来阐明取得改进的原因。以下是本研究的主要理解。实验结果表明，在低当量比条件下，少量臭氧的加入对天然气的自燃有明显的促进作用。在低当量比条件下，通过添加臭氧来改善燃烧，可以提高热效率，减少未燃烧的排放物，如THC和CO。然而，这种趋势随着臭氧浓度的增加而趋于饱和。达到饱和水平的最低臭氧浓度取决于等效比。对于高当量比，即使是小臭氧添加给爆震样燃烧，因此限制了最大发动机输出功率。燃烧分析表明，臭氧的加入提前了点火时间，提高了缸内最大压力和热释放率，大大降低了燃烧波动。然而，这些趋势随着臭氧浓度的增加而趋于饱和。粗略估算，在本研究的实验条件下，每加入100ppm的臭氧对应进气温度升高40℃。产生这么多的臭氧需要120w的电力。化学动力学计算结果表明，压缩冲程初期臭氧分解形成活性物质，是改善天然气点火和燃烧的主要原因。通过计算也证实了臭氧浓度的增加对着火性能的改善有饱和趋势。结果表明，这种趋势是由于HO_2和H_2O_2对天然气点火的影响有限。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