| The desire for increased fuel economy in conjuction with stringent emission regulations has nowadays, forced the motor gasoline engine to emply the electric fuel injection system (EFI). Based on the characteristics of the motor engine, the intak-port fuel injection (PFI) system is suitable which has employed on automotive engine successfully. However, the motor engine's small intake-port and high speed are limitation for learning from the automotive gasoline engine which makes the intake-port wall-film phenomenon receive more attention. How to reduce the wall-flim is becoming one of the most important issues for motor gasoline engine. In order to learn the intake-port wall-flim phenomenon, the experiment and simulatin methods are employed. The main research efforts and some results are as follows.1. Discussion of the way for wall-film entering the cylinder. There are two ways for wall-film entering the cylinder, one is wall-film accumulation and the other is wall-film cyclic strip-off. In order to find which way the wall-film is entering the cylinder for motor engine, some methods are studied. The experiment results show that the wall-film accumulation phenomenon can be checked by the measuring the AFR (air fuel ratio) when the engine control systerm working on N/P model. And it is show that there is no wall-film accumulation phenomenon for the studied motor engine. At the same time, the wall-film cyclic strip-off is chcked by measuring the AFR when the engine with no cooling air. The results show that with the increasment of the engine body temperature the value of the AFR and emission of HC are increased, but the NOX is declined which mean there is wall-film cyclic strip-off phenomenon for motorcycle gasoline engine. Meawhile, the wall-film cyclic strip-off is checked by changing the injection timing with intak valve closed and its experimental results also show this mothod can be used for checking the wall-film cyclic strip-off phenomenon.2. Model setup and validation. For learning more about the wall-film phenomenon in the intake port with closed valve injection, the simulation method is employed in this chapter. The first step for simulation is mesh set-up based on the basic method and selection of the sub-model. For this simulation task, the evaporation model is Dukowicz model, the breakup model is TAB model, and wall-film model isMundo Sommerfeld model. Then the validation of the model is started using the visualization method. The experimental results and simulation results show good agreement.3. Relationship of the influence factd and fuel evaporation rate under closed vale injection (CVI). When the CVI strategy is selected for PFI gasoline engine, the influences of nozzle position, spray angle, injection timing, back flow and temperature on wall-film evaporation are studied by numerical method. And some conclusions are received as follows.1) Two main influence facts on wall-film evaporation are engine temperature and intake air. When the engine at low temperature, spray targeting the upper junction of the intak-port and intake valve is good for wall-film evaporation, longer distance between the nozzle and targeting location such as 100mm is harmful to wall-film evaporation, back flow and advance injection timing can improve the wall-film evaporation. So the nozzle position, spray angle and engine structure should be consided together for designing the nozzle position.2) When the engine at low temperature, the fuel evaporation rate can be improved by modifying the influence facts. But the wall film cyclic strip-off can not be improved clealy.3) When the engine temperature is higher, the effects of the spray targing location, back flow on wall-film evaporation is still work. However, the injection timing's effect is weaker and the longer distance between the nozzle and targeting location will improve the wall-film evaporation rate.4. Relationship of the influence factd and fuel evaporation rate under open vale injection (OVI). In order to study how to improve fuel evaporaton under OVI condition, the same facts as CVI and more are studied with simulation method. Some conclusions are received as follows. 1) Higher velocity is good for fuel evaporation. For OVI, the longer diatance betweent the nozzle and intake valve is harmful to space evaporation but good for wall-film evaporation and the sum of space evaporation and wall-film evaporation showes that long diatance betweent the nozzle and intake valve decrease the fuel evaporation rate.The back flow can improve wall film evaporation rate and if the injection start at the beginning of the intake stroke the fuel evaporation rate can be increased.2) At wide open throttle (WOT), The spray targeting the upper junction of the intak-port and intake valve is good for wall-film evaporation; also the back flow is good for fuel evaporation rate. The injection timing should associate with intake air which means if the spray is impacted by high velocity intake air the fuel evaporation rate can be increased.3) For OVI, the engine temperature plays a more important role than the intake air and the fuel evaporation rate can be improved obviously at high engine temperature.4) Like the CVI, if the engine temperature is low the wall film cyclic strip can not be improved obviously by modifying the influence facts.5. The effect of twice fuel injection on fuel evaporation rate. From the analysis of closed valve injection and open valve injection, it is obviously that the relationship of the influence facts and fuel evaporation rate is different at different injection modules. However, neither of these two modules can solve the wall-film cyclic strip off obvoiusly. Then the twice fuel injection strategy is employed which mean the total amount of fuel needed for each cycle is divided into two parts. Part of the fuel needed is injected during the intake valve closed of explosion stroke to enable long fuel residence and other part is injected when the intake valve open of intake stroke to enble larger wall-film area and some particle entering the cylinder directly. Then the influence of twice fuel injection on wall-fim evaporation is studied. The simulation results show that twice fuel injection can utilize the intake air to improve space evaporation and larger the wall-film area. Moer fuel injectd during the explosion strok more fuel can be evaporated in the space. More fuel injected during the intake stroke more wall-film eavopration can be get. Compared of the sum of the space evaporation and wall-film evaporation more fuel injectd during the explosion stroke is better. For idle operation condition, the ratio of the fuel injcted in the exposion stroke and intake stroke is 1:1 can get best fuel evaporation rate. Meanwhile for heavy load condition if the fuel injected in exposion stroke is more than the fule injected in the intake stroke the better fuel evaporation rate can be received. However, for the heavy load condition the advantage of twice fuel injection is not clear.6. Reseach on the effects of twice fuel injection on fuel evaporation rate by test bed. In order to study the effects of the twice fuel injection on fuel evaporation rate, some researches is done using test bed. The experiment results indicate that the timing of the fuel injected during the explosion stroke has little effect on engine performance. Meawhile the timing of the fuel injected during intake stroke is different, at part throttle valve opening angle the engine power is decline with injection timing retarted while for wide throttle open the injection timing has little differenc because of high engine body temperature. Also it can be included from the experiment that more fuel injected during the explosion stroke can get more power and there is no diferrence between once fuel injection and twice fuel injection when the nozzle's flow coefficient ratio is small.
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