癸酸甲酯与正丁醇在低速柴油机中均质压燃燃烧与排放

Homogeneous Charge Compression Ignition Combustion and Emissions of Methyl Decanoate and n-Butanol in Low-Speed Diesel Engine

关键词:  癸酸甲酯  二冲程低速柴油机  正丁醇  充量均质压燃  氮氧化物排放

Key words:  Methyl decanoate  Two-stroke low speed diesel engine  n-Butanol  Homogeneous charge compression ignition  NO_x emission

摘要:

通过向生物柴油替代燃料癸酸甲酯（MD）中掺入一定比例的正丁醇（NBA），达到降低氮氧化物（NO_x）排放的目的。针对二冲程低速船用柴油机，建立了癸酸甲酯和正丁醇的混合燃料燃烧反应机理，并将Zeldovich氮氧化物反应机理作为子机理添加到燃烧反应机理中。构建出一个包含癸酸甲酯、正丁醇和详细的氮氧化物反应的完整燃烧反应机理。在燃料总摩尔分数一定的条件下，固定发动机转速与空气过量系数，将癸酸甲酯与正丁醇按不同比例进行混合，研究癸酸甲酯与正丁醇混合燃料在二冲程低速船用柴油机充量均质压燃（HCCI）模式下的燃烧与氮氧化物排放特性。结果显示，癸酸甲酯与正丁醇混合燃料HCCI燃烧产生的氮氧化物随正丁醇掺混比例的增加而减少。研究表明，在燃料总摩尔分数保持不变时，随着正丁醇混合比例的增加，燃料总热值减少，排气温度和缸内最高燃烧温度降低，对氮氧化物的生成有抑制作用，氮氧化物反应速率降低，排放量下降。同时，由于正丁醇掺混比例的增加导致混合燃料的C/H比下降，可以有效地降低燃烧过程中CO₂的排放。在保证发动机燃烧效率的条件下，癸酸甲酯和正丁醇的混合比例为1：1时，混合燃料在二冲程低速船用柴油机中HCCI燃烧的NO与NO₂排放量最低。

Abstract:

Nitrogen oxide （NO_x） emissions can be reduced by adding a certain proportion of n-butanol （NBA） into alternative fuel methyl decanoate （MD）. The combustion reaction mechanism of methyl decanoate and n-butanol was established for two-stroke low-speed marine diesel engine， and the Zeldovich NO_x reaction mechanism was added to the combustion reaction mechanism as a sub-mechanism， which constructed a complete combustion reaction mechanism containing methyl decanoate， n-butanol and detailed NO_x reaction. Under the condition that the total mole fraction of fuel is certain， fixed the engine speed and excess air coefficient， mixed methyl decanoate and n-butanol in different proportions， and explored the combustion and NO_x emission characteristics of methyl decanoate and n-butanol mixed fuel in two-stroke low-speed marine diesel engine with homogeneous charge compression ignition （HCCI） combustion. The results show that the emissions of NO_x produced by HCCI combustion of methyl decanoate and n-butanol mixture decrease with the increase of n-butanol blending ratio. The present research indicates when the total mole fraction of fuel remains unchanged， with the increase of n-butanol mixing ratio， the total heating value decrease， leading to the decrease of the exhaust temperature and in-cylinder peak temperature， the formation of NO_x is inhibited， the reaction rate of NO_x declines and the emission declines. Meanwhile， due to the increase of n-butanol blending ratio， it leads to the C/H ratio of mixed fuel decrease， which can effectively reduce CO₂ emissions during combustion. Under the condition of ensuring the engine combustion efficiency， when the mixing ratio of methyl decanoate and n-butanol is 1：1， the NO and NO₂ emissions in two-stroke low-speed marine diesel engine HCCI combustion are the lowest.