An Investigation On The Start Performance Of A SI Methanol EFI Engine

With the fast development of national economy,the demands of automobile rise with a high speed and we need more and more petroleum as a result. So we must look for substitute fuel in order to reduce the degree of depend petroleum. Deficient petroleum but abundant coal is the characteristic of energy sources in our country, so developing methanol made from coal is suitable our country's development.Methanol is a suitable substitute fuel of gasoline because its capabilities are similar with gasoline, moreover we can rise heat efficiency and reduce exhaust emission by using it. However, the primary disadvantage for SI methanol engine is harder to start in cold conditions, because the boiling point of methanol is higher than gasoline and methanol need much more power when it boils away.Not only exhaust emission limits become more stringent, but also measurement method is amended, deleting the first 40 seconds of idle after the start up phase. At the same time research results show that, as for SI (Spark Ignition) engine, HC and CO emissions during cold start phase take up very large proportion of vehicle emission limits under running mode, about 50%~80%, which makes it very important to optimize combustion and control exhaust emission of cold start phase. A lot of research work about the cold start characteristics home and abroad was done on gasoline engine,but little work was done on Methanol engine.Experiments were performed on a four-stroke, air-cooled, single cylinder, 125mL SI EFI engine, refitted from JH125 motorcycle engine. Thus injection pulse width and ignition advance angle of the engine could be adjusted flexibly to meet the demand of driving cycle. Besides a high speed, real time data acquisition system was developed in the experiment. Experimental study on the EFI Methanol engine was carried out from the aspects of both increasing first cycle firing reliability and to lower emission during cold start based on measurement and analysis of transient speed, cylinder pressure and exhaust emission. The main conclusions of experimental study are listed as below:(1) Environmental temperature is the key factor during the start phase. In the low-temperature environment, the evaporation rate of methanol islimited. When the surface temperature of the engine body dropped below 16°C, a reliable start can't be guaranteed even if increasing the injection. The key to starting methanol engine is improving evaporation conditions and accelerating the pace of methanol spray evaporation(2) The method of heating the air inlet can effectively increase the evaporation rate of methanol. Refer to heating methods, heating the outside of the air inlet with resistance wire is not enough, greater heat dissipation. better results is the installation of electric internal heating plug.(3) Spray width has a very important influence on the cold starting performance. With different intensity of the heating, reliable spray width and best value differs. Whether spray width smaller or larger, it will be difficult to form a good combustible gas mixture. The need of the fuel injection to ensure reliable start can be reduced by improving heating intensity and spray evaporation of methanol,(4) Ignition timing of the first cycle has a certain degree of influence on the performance of cold start. When ignition advance angle changes from 20°CA BTDC to 10°CA ATDC, starting speed reduces, cylinder combustion pressure drops until the engine can't start.(5) The reasonable control of injection timing to avoid the mixture from getting into the cylinder in misfire cycle .So that we can be assured a reliable start of the engine and reduce HC emission during the starting period.(6) The start performance of methanol engine can't be effectively improved by simply heating oil pipeline,because the fuel sprayed every cycle is so little that the energy it can carry can't guarantee the evaporation of methanol.(7) Injection into the air inlet using LPG can achieve reliable starter without heating. Proportion of the two types of fuel impact the start performance greatly, Increasing the proportion of LPG will make positive impact of the reliability of start. When the LPG spray width below 2.5ms, it is very difficult to achieve reliable starter even increase the injection of methanol. When blending LPG, the spray width always between 22ms～30ms which are less than 34ms by using heat-inlet method.(8) LPG injection timing has a certain affection on the performance of engine start when the method of LPG injection. Since the structural design of the physical and chemical properties of LPG decided LPG can enter the cylinder faster than methanol. Therefore, a reasonable injection timing can ensure two fuel into the cylinder in same cycle combustion. So that the reliability of start can be improved and emissions of HC can be reduced.