柴油/甲醇组合燃烧尾气中甲醛的检测

Measurement of formaldehyde emission from diesel/methanol compound combustion

利用气相色谱分析技术检测了柴油/甲醇组合燃烧(DMCC)尾气中的非常规排放物——甲醛.通过对不同采样方法和采样条件的比较,设计了采样系统,确定了用吸收液吸收的方法采集尾气中的甲醛.利用尾气中的甲醛与2,4-二硝基苯肼(DNPH)酸性饱和溶液反应生成甲醛腙的特性,通过检测甲醛腙的浓度来检测尾气中的甲醛含量.应用本方法检测一台采用DMCC燃烧模式的发动机尾气,结果表明,该方法可准确测量其尾气中的甲醛浓度.检测数据显示,当发动机运行DMCC燃烧模式时,相同转速下同一负荷时喷醇量越大,尾气中甲醛浓度越多;在相同的甲醇对柴油的替代率条件下,负荷越低尾气中甲醛浓度越高.

In this paper, gas chromatography （GC） is used to detect formaldehyde emissions from the engine with diesel/methanol compound combustion （DMCC）mode. A sampling system is designed through comparison and analysis among different sampling methods and conditions, and a method is provided to measure formaldehyde in the engine exhaust. Formaldehyde is absorbed by an acidic saturated solution of 2,4-dinitrophenyl hydrazine （DNPH） and converted to its hydrazone; the hydrazone is then extracted with CS_2 and quantitated by GC. The test method is applied to emissions of a DMCC engine and the results show that at the same rotation speed and the same load, as methanol in the fuel increases the formaldehyde in the exhaust also increases. Additionally, formaldehyde in exhaust is higher at low load than that at middle load while the engine speed and substitution rate of methanol to diesel in fuel remain same.