Study On The Ignition Time Control Of The CNG/Petrol Flexible Fuel Engine

In recent years, for fulfilling increasing energy needs and the more strict emission control regulations, people always make great efforts to develop all the clean energy besides crude oil, and have make a great advancement. In all the projects of clean energy, for the abundant reserves, low exhaust emissions and fuel economy, the Compressed Natural Gas (CNG) has become the most successful and potential substitute fuel, and is broadly noticed. For the restricting of natural gas pipe network and the level of gas engine study, the gasoline engine conversion is mainly flexible fuel engine. To consider the performance of engine using petrol, the flexible fuel engines don't modify the original engine structure. Therefore, the prominent performances of engine using natural gas have not been exerted because of the dissimilarity on the characteristic. The flexible fuel engine has problems with different degree to descend of dynamic performances and ascend of exhaust. According to the characteristics of the natural gas with high octane value and the slow flame velocity speed, we can adopt the method of augmenting ignition advance angle( opposite the gasoline electronic control system ) to advance the dynamic performance when the flexible fuel engine use the natural gas.This paper regards CNG/gasoline flexible fuel engine with electronic control inject add electronic control technology engine as the research object, according to the theory of gas electronic control and the distributorless ignition system, adopt the method of change the ignition reference signal carry out augmenting ignition advance angle while the flexible fuel engine use natural gas. This paper studies the affect of ignition advance angle to the dynamic performances and exhaust of the flexible fuel engine through test, and obtain the scheme of controlling the ignition advance angle. The result of the study has the important significance on dynamic performances loss reducing and further exhausts lowering, for the CNG/gasoline flexible fuel engine, and has important reference value for the performance optimized of other flexible fuel engine and ignition system development of the single fuel engine with natural gas.In order to carry out the signal of ignition reference advancement, the ignition control unit basing on the PIC SCM was designed and developed cooperatively. According to the effect factors and confirm principles of ignition advance angle, the engine test bed was established. For the need of test bed, the flexible connect axes was designed to resolve the problem of non-coaxial between the engine and power-measured machine, and the collecting system of the exhaust data experiment of the engine was also designed. According to the characteristic of dissimilar running order adopt different confirm rules while this paper ascertains regulatory scheme of ignition advance angle. At idle operation, exhaust of engine was primarily considered; at stable operations, dynamic performance was primarily considered. The following conclusion can be drawn from the contrast analysis of the data experiment:1. At running idle operation of the flexible fuel engine using natural gas, to decline ignition advance angle, the exhaust temperature can be increased, the emission of HC can be lowered. The ignition advance angle hasn't obvious effect on the emission of CO, the total change trend go up gradually with its increase. The ignition advance angle hasn't effect on the emission of NOx.2. At running stable operations of the flexible fuel engine using natural gas, the ignition advance angle that make engine give off the most torque augment or keep with speed increasing. At the same speed, the ignition advance angle that make engine give off the most torque don't decrease with load increasing, which augment or keep at high load and complete load.3. At running stable operations of the flexible fuel engine using natural gas, the ignition advance angle has obvious effect on the emission of HC and NOx. At middling load, the bigger of the increased ignition advance angle, the higher of the NOx emission; at low load, the bigger of the increased ignition advance angle, the higher of the HC emission; at high and complete load, to reduce the omission of CO and HC, the ignition advance angle should be increased bigger.4. At running stable operations of the flexible fuel engine using natural gas, the ignition advance angle has less effect on the emission of CO, which is mainly affected to be higher by the air-fuel ratio, and under high load condition, full load condition, as well by low load and rich mixture operating condition. Emission of CO can be reduced by increasing the ignition advance angle under the rich mixture operating condition.To sum up the above, it can be concluded that to adjust the ignition advance angle, while the flexible fuel engine using natural gas, can improve the dynamic performance enormously and can also reduce the emission amount greatly. To give full play to the advantage of the CNG, exact ignition advance angle control strategy is an important technology way. The paper shows the staggered work of the research, and the performance of the gas engine needs to be improved, and the further research can be carried out by improving the sparking energy, high compression ratio and pressurization technology to improve the dynamic performance of the flexible fuel engine.