Simulation Research On Combustion And Emission Of Direct Injection Spark-Ignition Methanol Engine

With rising petroleum prices and global warming being a dominantenvironmental issue, it seems that the use of alternative fuels in the future is inevitable.Methanol (CH3OH), also known as methyl alcohol, is considered to be one of themost favorable fuels for engines. This is because, as a liquid fuel, the storage,transportationand applications of methanol are similar to those of traditional gasolineand diesel fuels. Methanol has many desirable combustion and emissioncharacteristics: high octane number, indicating antiknock performance; high latentheat of vaporization; and excellent lean-burn properties. These properties makemethanol a good fuel for direct injection spark-ignition engines.The first step is to establish a simulation platform. The geometric modelis basedon a direct injection spark ignition engine, some modification on the model has beendone byPro/E of the CAD software, then the geometric model of*.stl style can beimported into FIRE to generate computation mesh, boundary conditions and initialconditions could be set in FIRE, and alsosome corresponding simulation models couldbe chosen in FIRE. At last, model verification has been done based on the experimentdatas. The verification results demonstrates that the model is right and it could beused in simulation for the engine.The influence of ignition timing and equivalence ratio on methanol engineperformance and emission characteristics has been investigated and simulated in thecase of homogeneous combustion mode. And using stratified combustion mode toinvestigate and simulate the influence of ignition timing and injection timing onmethanol engine performance and emissions. The simulation conclusionsas follows：1.In the case of homogeneous combustion mode, with the advance of ignitiontiming, the cylinder pressure, the cylinder temperature and the peak value of the heatrelease rate increase slowly, the constant volume level of combustion becomes better, and the unburned methanol and NOxemissions also go up slowly, however with theadvance of ignition timing the SOOT and CO emissions decrease slowly.2. In the case of homogeneous combustion mode,when the equivalence ratio is1.1, the peak value of the cylinder pressure and temperature increase a little, theamount of unburned methanol, CO and soot is large. When the equivalence ratio is0.9,the peak value of the cylinder pressure and temperature decrease a little, the amountof unburned methanol and NOxis also large. Only when the equivalence ratio is1, themethanol engine can get the best performance except for the high NOxemission level.3. In the case of stratified mode, injection timing is the key factor to fulfil thestratified mode. The simulation results demonstate that as the injection timing changesdifferent quality stratified mixtures can be formed with the influence of methanolatomization time and in-cylider flow field, in addition, with the injection timingadvanced the quality of stratified mixture is unsatifactory. If injection timing advanceexcessively,the methanol has insufficent time to evaporate and atomize, this lead tobad quality mixture and more difficult to form stratified mixture, this also lead tomore unburned methanol and SOOT emissions. From all the above it can draw aconclusion that when the injection is110oCA BTDC, the quality of stratified mixtureand the emission characteristics is satificatory.4. In the case of stratified mode, when the injection timing is constant, with theignition timing advanced, the cylinder pressure, the peak value of the in-cylindertemperature and the peak value of the heat release rate increase slowly, the constantvolume level of combustion becomes better, the NOxemissions also go up slowly, butthe unburned methanol, the CO and SOOT emissions represent conversely trend.