Study On Electronic-control Ignition System For Automotive Engine Fueled With Natural Gas

For the petroleum is becoming scarce, and the environmental regulations are more stringent day by day, the natural gas is becoming an excellent alternative fuel for automotive engine because of rich in reserves and power characteristics. Comparing with gasoline, the natural gas has higher octane number, and more spark energy is needed, so it is necessary to develop an electronic-control ignition system for engine fueled with natural gas. Further, test and optimization of ignition system is essential.In this paper, an electronic-control ignition system for automotive engine fueled with compressed natural gas was introduced, which was developed by our group independently. ATmega8 was adopted to control the ignition advance angle and charge time of primary circuit. The communication between PC and micro-controller was achieved through RS 232, so the control parameters can be adjusted in real time. For the simplified system was applied in a constant volume combustion chamber, the combustible mixture can be ignited at any situation.Two methods for spark energy measurement also were introduced in this paper: simulation load, direct measurement. The former one was developed according to SAE J973-1999 standard, Zener string was adopted as simulation load, the output energy of secondary coil can be measured quantitatively and effectively, which was introduced to evaluate the spark energy. The ignition control pulse and pulse interval and multi-pulse condition can be adjusted in real time, the effect for the spark energy can be analyzed, so the control parameters can be optimized. For the later method, current and voltage sensors were adopted, and oscilloscope was introduced to record the primary current and voltage, secondary voltage and current. For which we can calculated the energy stored in primary coil, output energy of secondary coil and energy conversion efficiency. The optimized result was matched with the former method.For more spark energy was needed by the CNG engine, another high-frequency ignition system was developed, more than 100 spark were introduced before the top dead center in compression stroke, the spark energy can be advanced effectively. For the winding was rolled by our group, casted by insulating resin. The system was powered by battery which was adopted by automotive engine, and speed signal was supplied by function generator, external interrupt was introduced as judge signal. For all the control parameters work together, the plug interval can be breakdown. The spark energy was measured by the direct measurement method, and it was more than tradition ignition system.Finally, bench test was toke out on CNG engine, the influence of ignition advance angle on dynamic and combustion characteristic was studied. The CNG engine was developed by JL465Q5 which was fueled gasoline, the fuel supply and multi-chip ECU was developed by our group. The test results show that: the peak pressure and pressure increase ratio is advanced with increasing of the ignition advancd angle, and the position is more closely to the top dead center; and the NOx, HC is increased, but the CO fluctuate littlely.