【作者】 彭红梅；

【导师】 姚春德；

【作者基本信息】 天津大学 ， 动力机械及工程， 2008， 博士

【摘要】 随着石油资源的日益减少,甲醇作为汽车的代用燃料,在我国有着广泛的应用前景。但是,甲醇燃料存在的问题是甲醛排放,甲醛是甲醇不完全燃烧的产物,对人体健康和大气环境存在危害。那么,准确检测发动机掺烧甲醇时尾气中的甲醛含量,研究甲醛的生成机理,对控制甲醛排放、推广甲醇燃料、缓解能源危机有很重要的意义。由于甲醇的十六烷值低,在压燃式发动机上应用困难,针对此问题,本课题组提出了柴油/甲醇组合燃烧理论(diesel/methanol compound combustion, DMCC),对甲醇以压燃方式工作提供了可行的应用途径。为了大力推广DMCC燃烧模式,需要全面了解该燃烧模式的排放情况,HC、CO、NOx等常规排放物的检测已经做了大量研究,目前需要对甲醛等非常规排放物进行检测。本研究就是基于上述基础开展的,根据掺烧甲醇燃料时发动机尾气HC多,成分复杂等特点,对甲醛检测方法进行了建立。该检测方法采用2,4-二硝基苯肼的酸性饱和溶液作为吸收液,吸收尾气中的醛类化合物,然后用二硫化碳萃取,利用气相色谱仪进行分析。该方法具有高度特异性,经过在发动机尾气检测中大量试用研究,确定该方法适合检测发动机掺烧甲醇燃料时的甲醛排放。该检测方法使用SP3420气相色谱仪,FID检测器,固定相1.5%OV-101/CW..D(80～100目)、2m×6mm的玻璃填充柱。气相色谱条件:柱温180℃,汽化室温度270℃,检测器温度270℃;载气流速(N2)为30mL/min,氢气30mL/min,空气300mL/min;进样量:5μL。该法采用外标法定量,在12.5～250的范围内呈现良好的线性关系;方法的检测限为0.45μg / mLμg / mL,最低检出浓度为0.6mg/m3;样品平行测定标准偏差在4.8%以内,在已知浓度的样品中加入甲醛标准溶液,甲醛回收率为97.2%～99.2%。该方法适合检测掺醇燃料发动机尾气中的甲醛浓度。利用该检测方法分别对压燃式和点燃式发动机燃用掺甲醇燃料时尾气中的甲醛排放进行检测。对DMCC尾气中的甲醛进行检测,检测结果表明:①与原机相比,DMCC燃烧模式甲醛排放显著增加,当甲醇掺烧比为25%时,甲醛排放在60×10-6以内,大约是原机的10倍,随着甲醇掺烧比的增加,甲醛排放逐渐增加;②当发动机转速相同,甲醇掺烧比相同时,低负荷时甲醛排放最高,中负荷时甲醛排放最低,随着负荷的增加,甲醛排放又逐渐升高;③氧化催化转化器对甲醛的净化效果不明显,甚至可以使甲醛排放增加,其转化效果与排气温度密切相关,当温度较低和较高时,可以使甲醛减少,当温度为300℃～410℃时,催化后甲醛排放反而增加;④本研究采用两种甲醇喷射方式进行对比:连续喷射和顺序喷射。检测结果表明,采用顺序喷射方式后,甲醛排放比连续喷射降低5.0～32.5%,在低负荷下甲醛排放降低幅度较大。此外,本研究还在点燃式发动机上进行了实验,实验使用了M0、M10、M20、M30四种油料,对四种燃料的甲醛排放进行检测,结果表明:与M0相比,汽油-甲醇燃料甲醛排放增加2～3倍,在M30大负荷和全负荷时,甲醛排放剧增,几乎达到M0的7倍,但是经过催化处理后,甲醛接近零排放,对大气环境不造成危害。在点燃式发动机上,三效催化转化器对甲醛排放有良好的净化效果。更多还原

【Abstract】 With the oil resource decreasing day by day, methanol plays an important role in future as a replacement fuel in our country. However, there is an unavoidable question that formaldehyde emission can harm atmospheric environment and human health. And it is well known that formaldehyde is the incomplete combustion product of methanol. Thus, in order to generalize the methanol fuel and control formaldehyde emission, it is valuable to detect the formaldehyde emission from methanol engine and to study the formaldehyde reaction mechanism in cylinder and exhaust pipe.It is difficult for methanol to be applied on compression ignition engine because of its low centane number. To resolve this problem, disel/methanol compound combustion (DMCC) was brought forward in the last few years. As regulated emissions, HC, CO, NOx, and PM from DMCC engine have been measured before, but the unregulated emissions such as formaldehyde need to be detected at present. In this paper, the measure method was build to detect the formaldehyde emission from methanol engine. The formaldehyde in the exhaust emission was collected by the acidic saturated solution of 2,4-dinitrophenyl hydrazine (2,4-DNPH) and converted to corresponding hydrazone derivative, and then the solution was extracted with carbon disulfide (CS2) and analyzed by a gas chromatography (GC) with a flame ionization detector (FID). The results showed that the measure method was applied to formaldehyde emissions of a methanol engine.A SP3420 GC was used to identify and quantify formaldehyde in the test method. To separate the carbonyl compounds, a chromatographic column (constant phase: 1.5%OV-101/CW..D; material: glass; 6 mm dia., and 2000 mm in length ) was used. The column temperature was 180℃, injector and detector temperature at 270℃with a nitrogen (N2) flow rate of 30 mL/min. The detector was FID, the flow rate of hydrogen (H2) was 30 mL/min and the air was 300 mL/min. The injection volume was 5μL. The liner regression equation was: y=ax+b;a=1.06E-003,b=-6.00E-001(R=0.9998), between 12.5μg /mL to 250μg /mLof target concentration in the air. The limit of detection was 0.45μg / mL, and the limit of quantitation in the samples of exhaust was 0.6 mg/m3. The relative standard deviation was less than 4.8%. The average recoveries were 97.2%～99.2%. The method is suitable to determine formaldehyde of a methanol engine.The measure method was applied to determine the formaldehyde emission from a DMCC engine, the results showed as follows:①Compare to diesel engine, the formaldehyde concentration from DMCC engine rised rapidly. The formaldehyde emission is about 60×10-6 when the methanol proportion is 25%, which was about 10 times higher than that of diesel engine.At same-load, with the methanol fraction increasing the formaldehyde emission increased.②When the methanol proportion is same, the formaldehyde concentration is the highest at low-load, the lowest at medium-load.③The formaldehyde emission could not be eliminated completely by the catalyst, and the exhaust temperature was a key factor for the oxidation catalyst’s effect. When the exhaust temperature was lower than 300℃or higher than 410℃, the formaldehyde emission was cut down by the catalyst. But the catalyst effect was negatively and the formaldehyde emission increased if the exhaust temperature between 300℃to 410℃.④Two methanol inject ways were used in this work, continuous and sequential. The results showed that the formaldehyde concentration of sequential was decreased 5～32.5% than that of continuous.The measure method was used to determine the formaldehyde emission of a gasoline/ diesel engine. Four types of blends were used in this work: M0, M10, M20, and M30. The results showed that the formaldehyde concentration of gasoline/engine was 2~3 times as gasoline engine in normal load. To us enjoys, the three ways catalyst eliminated the formaldehyde completely in SI engine.更多还原