Emission Characteristics And Formation Mechanism Of Carbonyl Compounds In Diesel Engine Fueled With Alcohols-diesel Blends

Due to the presence of carbonyl compound emissions in higher concentration for engines fueled with methanol/ethanol-diesel blends, this study focuses on the emission characteristics and formation mechanism of carbonyl compounds (CBCs) in diesel engine fueled with alcohols-diesel blends. The CBCs were gathered and analyzed by the method of 2, 4-dinitrophenylhydrazine (DNPH) derivative and high-performance liquid chromatography, and the emission characteristics and formation history of CBCs for alcohols-diesel blends were investigated. Based on the models of spray and combustion, the numerical simulation during combustion process was carried out for the CBCs of methanol/diesel blends. The major achievements and conclusions of this dissertation are listed as follows:1. Based on DNPH cartridge and HPLC, the detection of CBCs during combustion process and in the exhaust emissions from engines fueled with alcohols-diesel blends were studied, and the sampling and analysis strategies were established systematically. These paved the way to study the formation history of CBCs in engine combustion process and CBCs emission characteristics.2. By the means of measuring the CBC emissions during the constant speed/varying load tests, the influence of alcohols/diesel ratio, engine speed and load on the CBC emissions was investigated. The engine experimental results indicated that for either pure diesel fuel or alcohols/diesel blends, formaldehyde and acetaldehyde were most abundant in CBC emissions. The alcohols/diesel ratio, engine speed and load exhibited profound effects on CBC emissions.3. The influences of pure diesel (M0), two kinds of methanol-diesel blends (M8, M13), two kinds of ethanol-diesel blends (E10, E20) on the engine combustion process and CBC formation history were studied. The experimental data indicated that the introduction of methanol/ethanol-diesel blends in diesel engine led to an increase in both highest cylinder pressure and temperature. In addition, the ignition timing was advanced; the pressure and temperature increase rate accelerated; and heat release rate was improved. For the alcohols-diesel blends, formaldehyde and acetaldehyde were mostly abundant in CBCs at different crankshaft angle during combustion process, followed by acrolein, propionaldehyde, butyraldehyde, cyclohexanone, p-tolualdehyde and hexaldehyde. And these eight kinds of CBCs mentioned above accounted for 90% of total CBC emissions. Other CBCs were occasionally present in the samples and showed unobvious variation trends.4. The spray and combustion of both pure diesel and methanol/diesel blends were studied by means of theoretical analysis and numerical simulation, and the results obtained were also compared with experimental data. The experimental data showed that the methanol/diesel blends could improve the mixture quality and turbulent kinetic energy in the cylinder, and the average combustion temperature for the methanol/diesel blends was higher than that for pure diesel fuel. These would help to accelerate the combustion development, boost the combustion efficiency and decrease the formation of incomplete combustion products. Due to high latent heat of vaporization and short injection penetration distance of the methanol/diesel blends, a large amount of CBCs would originate from quenching layer around cylinder wall. The incomplete combustion compounds stayed in the quenching layer emitted with other combustion products from the engine, and caused higher CBC emission in the engine exhaust pipe.