Development Of A Multi-Point Sequential Injection System And Experimental Research On A Compressed Natural Gas Engine

Engines with high efficiency, low fuel consumption and low emissions are an effective way to solve energy crisis and environment pollution. Among diverse alternative fuels, natural gas is the most favorable one, due to its abundant reserves and low cost. Multi-point sequential electronically controlled system can improve mixture distribution in different cylinders and extend the lean limits of natural gas engines. Therefore, electronically controlled system and data acquisition system were first developed for a natural gas engine test bench and then, was used to investigate the effect of various parameters on combustion characteristics of the engine.Based on an InfineonXC164CS evaluation board and modularized software design method, an electronically controlled multi-point sequential injection system and high energy ignition system were developed, which could precisely control injection duration, injection timing, ignition energy as well as ignition timing. With the help of "Visual C++" software, a monitoring system was also developed to diagnose the working processes of the engine, modify the control parameters in real-time and transmit data between personal computer and electronically controlled unit through asynchronous serial communication.Based on a PCI2006 high speed A/D data acquisition card, a cylinder pressure acquisition and combustion analysis system were established by using the object-oriented method of Visual C++ software, which could monitor and save the cylinder pressure in real-time. The latter could be used to calculate heat release ratio and other combustion characteristics, such as indicted mean effective pressure (IMEP), ignition timing, combustion duration and coefficient of variation in IMEP.The influence of ignition timing, excess air ratio, engine speed, throttle positions on the combustion characteristics of the natural gas engine was conducted. The results showed that IMEP and the ratio of heat release reach their peaks when the maximum cylinder pressure point is at about 15°CA after top dead center (TDC) and at about 10°CA after TDC, respectively. Changes of ignition delay are within 2°CA when ignition timing varies from 20°CA before TDC to 45°CA before TDC, keeping the coefficient of variation in IMEP below 6%. Changes of ignition timing can come to 8°CA while excess air ratio changes from 0.85 to 1.3.