| Low and high temperature two-stage combustion can avoid the island of NOxand PM generating by controlling the temperature and concentration. In order tomeet the requirements of the more rigorous emission regulations, strengthenedmixing method can be introduced, which can make the oil and gas mix more evenlyand prolong two stage ignition delay period, resulting in burning more completelyand the emissions concentration of NOx and PM reducing further.An experiment study has been made based on the low and high temperaturetwo-stage combustion. In the inlet manifold of the CA6DL2-35E3electronicallycontrolled high pressure common rail diesel engine, we spray into the right amountof petrol and partly replace diesel by gasoline in low temperature burning stagemaking the gas mix more evenly, whicn can effectively avoid the formation of theoxygen-rich and oil-rich region in cylinder and prolong two stage ignition delayperiod. By the method of research in stages, firstly in order to make the emissions ofNOx and PM on the optimal performance as well as the emissions of HC and CO nottoo much, we investigated and optimized the of the impact factors of gasolineinjection quantity, pre-injection timing and pre-injection diesel quantity in the firstphase. Then, we investigated the influence of main injection timing, main injectiondiesel quantity and rail pressure on the double stage combustion and we alsoconducted load expanding. In order to further reduce concentration of NOx and PMemission in the double stage combustion, dual-stage combustion of fuels wasreasonably organized and analyzed compared with the double phase combustion.The main research work and conclusions are as follows:1. Establishment of the experiment bench. The CA6DL2-35E3diesel engineintake port has been transformed, adding gasoline supply injection system. Control of the amount of gasoline was realized by the self-made gasoline injection controlsystem and the main injection timing, injection time, main injection fuel quantity arecontrolled by the original machine INCA calibration system. Combustion analyzerwas used to collect data of the cylinder; LabView software was used to collect dataof dynamometer; emission analyzer was used to collect emission data; smokemeterwas used to measure the smoke value etc.2. The low temperature premixed combustion experimental research showedthat the method, injection of gasoline in the double stage combustion, is feasible andthe amount of gasoline has no effect on the peak heat release rate time in the firststage. By increasing gasoline injection quantity moderately, concentrations of NOxwere all less than100ppm and content smoke were all below0.5%. Diesel fuelinjection timing was advanced to40°CA BTDC and light-off starting point were allabout17°CA BTDC, heat release rate light-off time and the shape of heat releaserate curve basically remained unchanged. lower diesel fuel injection quantity canreduce the emission concentration of NOx and PM at the same time, but thisincreased the possibility of a fire.3. The specificity analysis of dual-stage combustion of fuels: high temperaturecan lead to the advance of the combustion starting point of the first stage; the firststage heat release rate curve of the dual phase combustion was basically the samewith the only one stage combustion heat release rate curve. Delay of the maininjection timing had almost no effect for the first stage heat release rate curve andpeak value the crankshaft angle corresponding to high temperature combustion heatrelease rate peak value also postponed with the heat release rate peak value dropping.When the main injection timing is4°CA BTDC, heat is maximum and burning is themost completely. Main injection timing almost did not affect the emission amount ofHC. With the increase of the main injection diesel quantity, the starting temperatureof the low temperature combustion increased and the combustion starting pointadvanced. With the main injection diesel quantity increasing from5to29mg/cyc, thecurve of CO, HC, NOx and extinction smoke did not have turning point. 4. Selection of the optimum parameters. Considering the influence of injectionparameters on the emissions and be, so drawing contour map and selecting theoptimal injection low-temperature combustion parameters as follows: gasoline was5.36kg/h, pre injection timing was-45°CA ATDC, diesel fuel injection quantitywas2.5kg/h. The optimization of the second stage parameters：main injection timingwas2°CA ATDC, main injection diesel quantity was90mg/cyc. At this time, theemission of CO was960ppm, smoke value was1.42%, HC was369ppm, NOxemission was471ppm, the effective fuel consumption rate was232.02g/(kW.h).5. Influence of the rail pressure on dual-stage combustion of fuels. With themoderate increase of rail pressure, cylinder pressure also increased and the sprayatomization quality as well as injection rate of diesel in the main pre spray twostages were all improved, causing petrol and diesel mixture uniformity and burningrate improved, combustion heat release rate peak value of the two stages increased.But too high rail pressure will spray part of the diesel into the cylinder wall and it isdifficult to mix with gasoline completely, causing decline of the heat release rate andoscillation of heat release rate curve. After the injection pressure rising, atomizationquality turned good, high-temperature region widen, extinction smoke reducedsignificantly, NOx increased, combustion temperature rised, which was conducive tothe oxidation of CO furthermore. The rail pressure change had no effect on HC.6. Dual-stage combustion of fuels compared to low and high temperaturetwo-stage combustion, the concentration of CO and HC emissions increased, theeffective fuel consumption rate also increased, but NOx emission decreased by39%,extinction smoke decreased by29%, which achieved the targets of lowerconcentration of NOx and PM emissions. |
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