Research On Combustion Characteristics For Direct Injection Piston Aviation Engine

At present, piston aviation engine are almost use carburetor as its main fuelsupply system in our country. But the carburetor fuel supply system has a lowprecision of transient response and uneven mixture control in each cylinder and proneto ice and fire danger. The modern electronic controlled GDI technology willaccurately control the cylinder mixture formation and combustion process of theengine. Adopting the modern GDI to improve the flight performance and security andfuel compatibility of piston aviation engine become a new research trend. In thispaper, a single cylinder testing engine was developed to make a research forcombustion characteristic of the aviation direction injection engine. The main workare as follows:1. Based on the ROTAX914carburetor piston aviation engine, a single cylindertesting engine was developed, including the design of low-pressure directinjection fuel supply system, the development of direct injection combustionsystem, the design of the electronic control system and cooling system design,etc.2. A test bench was design and set up to make an experiment research on thecombustion characteristics for direction injection piston aviation engine. Theinfluences of injection phase, injection duration, injection pressure, ignitionadvance angle and low octane fuel to the combustion characteristics of enginewere researched. The results of the study are as follows:(1). There is a best start of injection time for the direct injection aviation engine.When the start of injection timing is at the beginning of the compression stroke,the combustion efficiency get higher and the combustion cyclic variations getlower. There is a limit time for the end of injection in the low-pressure injectionsystem, when the end of the injection time over the limit, the engine burningdeteriorated sharply. The best start of injection time and the limit time for the endof injection advance accordingly with the increasing of engine speed and load.(2). With the decreasing of the injection duration, the peak cylinder pressure and therate of pressure rise are also decreased. The combustion phase delay accordinglyand combustion cyclic variations get higher. When the injection duration reduced to3ms at a later time of the end of the injection, the combustion cyclic variationsrising sharply. Reduce the injection pressure will delay the CA50and extendedthe rapid combustion period. When the injection pressure dropped to4.5bar at alate end of injection time, the combustion stability drop sharply.(3). Advance the ignition time will increase the peak cylinder pressure and the rate ofpressure rise. The combustion phase will advance and combustion efficiency willincrease also. When take the low octane number fuel as the test fuel, knock hadappeared in the single cylinder testing engine. Delay the ignition advance anglewill a effective way to reduce the knock intensity.