Study On The Characteristics Of Gaseous And PM Emissions From Heavy-duty Diesel Engines With DMDF

With the increasing of the ratio of dependence of importing oil and thedevelopment of the low emission legislations, searching for clean and efficientalternative energy has been one of the important ways to relieve the energy tentionand reduce harmful emissions from engines. As a renewable fuel, methanol can bederived from a wealth of sources.There is also a mature processing technique andsuperior physicochemical properties of methanol. With diesel methanol dual fuel(DMDF), methanol used in diesel engine can be not only a substitute for diesel, butcan also reduce engine harmful emissions, which are of great significance toenergy-saving and emission-reduction. Based on combustion characteristics of DMDF,HCHO unregulated emission, smoke emission and particulate matter emission ofusing DMDF combustion mode with simple aftertreatment technique engine werestudied in this study. The main research work and conclusion gained are as follows:Firstly, comparing methods of formaldehyde detection while the engine burnedmethanol, and detecting formaldehyde emissions in the same operating conditionunder different blending ratio. Gas chromatography (GC),high performance liquidchromatography(HPLC) and Fourier Transform Infrared Spectrum(FTIR) these threemethods were used to detect. The test results showed that the detection value ofFourier Transform Infrared Spectrum was higher than that of chromatography.Formaldehyde detection using Gas chromatography was in good agreement withusing high performance liquid chromatography.They were both high precision butcomplex and couldn’t achieve real-time online detection. Fourier Transform InfraredSpectrum was simple to operate and could achieve real-time online detection, whilethe detection precision decreased because of the disturbance of other materials and theinfluence of system calibration.Secondly, after modification, both turbocharged inter-cooled mechanical pumpdiesel engine and supercharged inter-cooled unit-pump diesel engine could achieveDMDF combustion. The paper investigated the combustion characteristics, the effectsof substitution rate, inlet temperature and exhaust back pressure on formaldehydeunregulated emissions, dry soot, light-proof smoke, particulate quantity distributionand the mass concentration of particulate. The results showed that compared withtraditional diesel engine, maximum firing pressure of DMDF was higher, and with theincreasing of substitution rate, the pressure increased. DMDF combustion modechanged the form of heat release rate of pure diesel mode, the ignition timing delayed,the peak heat release rate increased and the initial heat release rate rose sharply. InDMDF combustion mode, the proportion of the diffusion combustion reduced, while the proportion of premixed combustion increased. At low load conditions, the curvesof the heat release rate was single peak of homogeneous charge compression ignition,while at high load conditions was double peaks of quasi homogeneous premixedcombustion. Compared with pure diesel combustion mode, the formaldehydeemissions of DMDF combustion mode increased greatly, and with the increasing ofsubstitution rate, the formaldehyde emissions increased gradually. Paricularly at highsubstitution rate, the formaldehyde emissions in DMDF combustion mode was tenfoldthan that in pure diesel combustion mode. However, DMDF combustion mode couldsignificantly reduce dry soot and light-proof smoke of engine. Dry soot andlight-proof smoke reduced with the increasing of substitution rate, the biggest drop upto70%. High inlet temperature could reduce the production of formaldehyde to someextent. With the decreasing of inlet temperature, particulate quantity distribution andthe mass concentration reduced, while they increased with the increasing of exhaustback pressure.Finally, the influences of DMDF combustion mode with simple aftertreatmenttechniques on engine harmful emissions were investigated. The result showed thatDMDF combustion mode with double DOC(DDCO) and DOC closely seriallycoupled with a POC(DOC+POC) could significantly reduce engine regulated gasemissions (HC,CO,NOX), HCHO unregulated emission, smoke emission(dry soot andlight-proof smoke) and particulate emission. They could also significantly increasethe purification efficiency of dry soot by POC employed. The average purificationefficiency could gain over60%, the best one is90%. As a contrast, the purificationefficiency of dry soot by POC in pure diesel mode was just around30%.The results also indicated that DMDF combustion mode could reduce theproduction of engine harmful emissions without SCR, and it has now passed theChina III and IV emission regulations certification. DMDF combustion mode couldfurther reduce NOXand PM emission and have the potential to meet the requirementsof futural more stringent emission legislation. The research has provided a newtechnical route for reducing oil consumption and engine emissions.