| The demand for oil is increasing every day because of the increase of vehicle populationin the world, many car manufacturers have been focused on the research on energy savingtechnologies and alternate fuel. Compression ratio is an important factor which influencesengine efficiency, but there is knock if compressure ratio is too high, and it will affect engineworking. There is pumping loss when engine uses a throttle, and pumping loss will consumemechanical energy, so it will influence engine efficiency too. EGR is used to reduce NOxemission originally, because it can increase exhaust gas in cylinder, and this will reducepumping loss. Octane number of methanol is high, and its antiknock property is good, it issuitable for high compression ratio engine, and its flame propagation velocity is fast, so itcan combust in high EGR ratio condition. For the sake of improving engine efficiency fromincreasing compression ratio and reducing pumping loss, our team has developed a sparkignition methanol engine with high compression ratio, and has done the research onapplication of EGR to the methanol engine, the main contents of this paper are as follow:1. Modification and calibration of prototype engine. A2L diesel engine has been modifiedinto a spark ignition methanol engine, calibrations of methanol injection and ignitionadvance angle for4loads at1400r/min have been finished subsequently, the maximumtorque is153.4N·m, and its ignition advance angle is18°CA BTDC, its fuel consumption is11.78kg/h.2. Research on application of homogenous EGR without throttle. In order to reducepumping loss maximumly, throttle was opened to maximum, without throttle meaned thatthrottle was opened to maximum in the paper, EGR was used to control the amount of air incylinder without throttle, the influences of EGR ratio and ignition advance angle on torque inthe condition of stoichiometric mixture have been researched. The maximum EGR ratio is53.3%, its torque is57N·m, and its ignition advance angle is33°CA BTDC. When the loadis controlled by using EGR, the larger EGR ratio, the lower fuel consumption rate, and thelarger corresponding ignition advance angle, the minmum torque is55.5N·m. In the sameEGR ratio, when ignition advance angle is smaller than27°CA BTDC, the larger ignitionadvance angle, the higher torque; when ignition advance angle is larger than27°CA BTDC,the larger ignition advance angle, the lower torque. Fuel consumption rate of applying EGRwithout throttle is higher than that of not applying EGR when torque is lower than95N·m. 3. Research on application of homogenous EGR at middle and low load with throttle.Throttle opening was reduced to reduce EGR ratio. Torque of25%load at20%EGR ratioand ignition advance angle of21°CA BTDC is43.8N·m, it is3.6N·m higher than that ofnot applying EGR, and effective fuel consumption rate is34.3g/(kW·h) lower than that ofnot applying EGR, and effective therma efficiency is increased by1%. Torque of50%load at30%EGR ratio and ignition advance angle of24°CA BTDC is84.1N·m, it is8.5N·mhigher than that of not applying EGR, and effective fuel consumption rate is70.6g/(kW·h)lower than that of not applying EGR, and effective therma efficiency is increased by3.3%.4. Research on strategy to realize stratified EGR. Exhaust gas of EGR going into cylinderthrough a EGR pipe will flow along cylinder periphery. When EGR pressure is100kPa,average EGR ratio is about3%, EGR ratio of central part in lateral section upon bowl islower, there is no EGR stratification in bowl. When EGR pressure is130kPa, average EGRratio is about35%, when EGR pressure is160kPa, average EGR ratio is about52%, for eachof them, EGR ratio of central part in lateral section upon bowl is higher, there is no EGRstratification in bowl. When EGR is stopped at480°CA, EGR ratio of central part in lateralsection upon bowl is higher, there is no EGR stratification in bowl, average EGR ratio isabout47%. When EGR is stopped at450°CA or420°CA, for each of them, EGR ratio ofcentral part in lateral section upon bowl is higher, there is no EGR stratification in bowl,average EGR ratios are larger than38%. When chamber bowl is modified into deep column,EGR ratio of central part in lateral section upon bowl is lower, EGR ratio of central part inlateral section of bowl is higher. When chamber bowl is modified into shallow column, EGRratios of central part in lateral section upon bowl and in bowl are lower. When chamber bowlis canceled, EGR ratio of most area is lower, but EGR ratio of periphery of cylinder top islower too.5. Research on influence of EGR stratification on combustion. In the same igntionadvance angle, pressure and heat release rate peak values of stratified EGR are higher andearlier than those of homogenous EGR. Combustion delay period of homogenous EGR islonger than that of stratified EGR. |
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