Study On Combustion And Emissions Performance Of DME-Methanol Engine

The development of DME-methanol fuels as a supplement to oil resources,has far-reaching implications for our country ’s energy security. After applicationof DME-methanol mixed with diesel fuel to a compression ignition engineallows it to obtain basic no-smoke emission, low nitrogen oxide (NOx) effect,promote environment improvements.In this paper, based on4100Q engine, the author established combustionchamber model and studied internal flow and emissions field of methanol,dimethyl ether and diesel fuel under different states to determine the optimalblending ratio, and based on the optimal blending ratio to determine theoptimal injection parameters. The main research work are as follows:(1) The author use AVL-FIRE software to establish combustion chambermodel of4100Q engine and mesh it. By comparing the simulation value andexperimental values, this paper verified the reasonableness of the combustionchamber model.(2)Fix the quality ration of diesel as70%, add methanol as12%,8%,4%and0%respectively to the diesel, and the rest add DME. Study the cylindertemperature, cylinder pressure, accumulated heat release, NOx and Sootemissions of the four mixed fuels in2200r/min under high load condition, and compare them with diesel. The simulation shows that under high load conditions,with the increase of methanol content in the fuel blends, cylinder pressuregradually increases, the crankshaft angle position of the highest cylinderpressure unchanged; with the increase of methanol content in the fuel blends, thepeak value of the rate of heat release curve decreases, the highest cylindertemperature decreases, the emission of NOx decreases, but the emission of Sootincreases.(3)Fix the quality ration of methanol as12%, add diesel as70%,60%,50%and40%respectively to the fuel， and the rest add DME. Study the combustionand emissions of the four mixed fuels in2200r/min under high load condition,and compare them with diesel. The simulation shows that under high loadconditions, with the decrease of diesel content in the fuel blends, cylinderpressure gradually decreases, the crankshaft angle position of the highestcylinder pressure unchanged, the accumulated heat releases increases, thehighest cylinder temperature decreases; with the decrease of diesel content in thefuel blends,the emission of NOx increases, but the emission of Sootdecreases.The optimal blending ration of blended fuel can be obtained fromabove. The final selection of the content of diesel, methanol and DME arerespectively70%,12%and18%.(5)The author has studied the effect of injection parameters includinginjection timing, injection duration and injection law to combustion andemission characteristics of the optimal blending fuels. The results show that: with injection timing advanced, cylinder pressure and temperature decreases.Besides, NOxexhaust is obviously lower, but Soot exhaust resembles; withinjection duration increases, cylinder pressure and temperature are alsodecreases and the peak value of temperature delays. NOxexhaust is lower, butSoot exhaust almost has no difference. By adopting injection law of first slowthen fast, NOxexhaust is much lower than original engine. Using first slow thenfast injection law, cylinder pressure and temperature are both decreases, NOxexhaust is lowest, but Soot exhaust increases.