| 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. |
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