Experimental Study On First Cycle Cold Start And Catalyst Fast Light-off Of An EFI LPG Engine

With the fast development of automobile industry, the share of air pollutionborn by automobile emission has caused popular attention, so European Unionestablished and implemented more stringent emission regulations. Not only exhaustemission 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 timeresearch results show that, as for SI (Spark Ignition) engine, HC and CO emissionsduring cold start phase take up very large proportion of vehicle emission limitsunder running mode, about 50%~80%, which makes it very important to optimizecombustion and control exhaust emission of cold start phase. And the exhausting petroleum resource is another serious problem forautomobile. Driven by both severe oil crisis and environment protection, LPGbecomes a kind of alternative fuel in possession of market potential in the presentbecause of less exhaust emission and better fuel economy, and LPG engine hasturned into one of study hotshots in internal combustion engine area. To meet the future stringent emission regulation, for example Euro Ⅲ andEuro Ⅳ, that LPG engine adopts EFI (Electronic Fuel Injection) and matches TWC(Three Way Catalyst) has become a trend and need for present development.Meanwhile, LPG engine also confronts the problem during cold start phase, butlittle work was done on LPG engine, because a lot of research work about the coldstart characteristics home and abroad was done on gasoline engine. The objectiveof the paper is to perform experimental study to reduce emission of cold start onEFI LPG engine with TWC, especially HC emission, so as to meet the limits ofEuro Ⅲ and Euro Ⅳ. The test methods and main experimental contents are described as follows: Experiments were performed on a four-stroke, air-cooled, single cylinder,125mL SI EFI LPG engine with TWC, refitted from JH125 motorcycle engine,and with the help of exhaust oxygen sensor, closed-loop control of the engine wasimplemented. The gaseous LPG injection was introduced. A vessel was used tostabilize the pressure and the KN3-2B nozzle made in Japan was used. At the sametime the DC-CDI (Digital Controlled Capacitor Discharge Ignition) system wasadopted. The system could supply steady ignition energy and adjust the ignitiontiming. Thus air/fuel ratio and ignition advance angle of the engine could beadjusted flexibly to meet the demand of driving cycle. Besides a high speed, realtime data acquisition system was developed in the experiment. Experimental studyon the EFI LPG engine was carried out from the aspects of both increasing firstcycle firing reliability and fast light-off of TWC, in order to lower emission duringcold start and meet regulation based on measurement and analysis of transientspeed, cylinder pressure and exhaust emission. The main conclusions of experimental study are listed as below: 1, Experimental study of first cycle emission performance on cycle by cyclecontrol strategy.iv吉林大学硕士学位论文 a, The injection pulse width is the key factor for the characteristics of ignition cycle during the cold start. It is possible to realize the ideal ignition cycle, i.e., the combustion occurs after the first ignition if the first injection pulse width and timing are controlled reasonably, so HC emission is lowered remarkably. Moreover, under several ambient temperatures and start voltages there is a range of excess air coefficient from 0.4 to 0.68, where the engine shows good performance. And at the optimum injection pulse width of 8ms, with excess air coefficient of 0.6, the reliability of first cycle firing can be assured. b, Ignition advance angle affects first cycle combustion performance of EFI LPG engine to some extent. At the optimum injection pulse width, with the delay of ignition timing, the engine start speed become...