Experiment On Diesel Engine With Intake Premixed Methanol And Simulation Of Air/Methanol Mixture Formation

China is abundant in coal resource, less storage in natural gas and poor in oil. Methanol, made from coal, is the most promising alternative fuel for internal combustion engines. Methanol applied directly to diesel engines is very difficult because of the lower cetane number of methanol, while using an appropriate method of methanol blended, diesel engines can well operate on diesel and methanol, and intake premixed methanol appears to be an attractive means in several usual ways of diesel engines fueled with methanol. However, when methanol is used in turbocharged diesel engines, it is very necessary to do many researches on methanol premixed ratio and methanol atomization at different operation conditions, as well as intake temperature descent with methanol premixed. In the paper, experimental study on a turbocharged diesel engine with methanol premixed is conducted, and methanol/air mixture formation is simulated.To investigate the turbocharged diesel engine operating with methanol premixed within the range of full conditions, a methanol injection system was designed according to the characteristics of methanol premixed in induction system. Used the intake pressure and engine speed signals as identification of engine operating conditions and methanol injection control, 4B26 diesel engine was reformed to the dual fuel engine with methanol premixed. The test results show that the methanol injection system meets the demand of the dual fuel engine, controlling the methanol injection flexibly at different operation conditions. In dual fuel operation mode, methanol premixed ratio should be optimized so as to achieve better fuel economy than diesel used only. When the intake pressure is higher than 130kPa, the inlet flow state plays an important role in combustion process of dual fuel mode, and the mass of methanol blended is limited by knock, and knock tendency can be reduced by means of diesel fuel injection timing delayed. Compared to single diesel direct injection, the dual fuel mode can get better fuel economy and lower exhaust temperature. Although diesel compound combustion produces high CO and HC emissions than diesel combustion only, methanol premixed in port can reduce NOx and soot emissions simultaneously.Utilized numerical simulation tool, cylinder air temperature and methanol distribution characteristics of diesel engine intake methanol premixed were studied to guide the methanol/diesel dual fuel engine modification. Methanol sprayed into induction system covers diesel engine induction process and methanol injection system. It is important to investigate the mechanism of intake flow and air-methanol mixture formation inside internal combustion engine, which is one of the essential theories of methanol electronic control injection. Based on KIVA-3V code, the numerical model of air and methanol mixing process in diesel engine, including droplet collision and wall film dynamic model, was analyzed and developed. The structured hexahedral mesh for exact helical intake port-valve-cylinder shape was studied and the initial grid of 4B26 model was generated with ICEM-CFD software. Added and modified valve motion model algorithm, the grid can succeed in checking under KIVA-3V code.Completed input files of KIVA-3V code and used tested data as the initial and boundary conditions, the transient simulation model for 4B26 turbocharged engine with induction and compression stroke was created. The process of the diesel engine induction and compression at different conditions were simulated. The calculations show that the structure of cylinder velocity fields is insensitive to engine speed and load, and has similar change process at different operation conditions. During the compression stroke, there is always vortex motion in cylinder. The flow characteristics in cylinder mean that the diesel engine operating condition has little effect on the process of methanol atomization and contribution in cylinder by methanol injection control.The transient mixing process of methanol injected into the diesel engine induction system was simulated. The calculations show that methanol film evaporation is important to the methanol mixing formation. There is a better methanol injection timing at a given engine operation condition, which can obtain a good compromise between methanol film mass and film evaporation. Methanol injection orientation is determined by the principle of decreasing methanol film. When methanol is not directly sprayed onto inlet valve surface, methanol is almost in liquid state before the valve is opened. The methanol vaporization mainly carries out in engine induction stroke, nearly gaseous methanol into cylinder. When sprayed directly onto the valve surface, methanol droplets collide with the hot surface of the valve, resulting in rapid evaporation of droplet. Most of the methanol droplets have become gaseous form before the valve opened. High air temperature, making both droplets and film vaporize fast, has more influence on methanol mixture process than hot port wall which mostly improves film evaporation. At the time of diesel injected, methanol concentration in cylinder is stratified more obviously at cylinder axis direction than that at cylinder radial direction under different methanol injection orientation and timing. Methanol premixed can reduce the intake temperature. At 1800r/min and 2200r/min with high methanol premixed ratio, the cylinder temperature with methanol premixed is decreased by 52K and 43K respectively before top death center 10°CA compared with that without methanol premixed...