Dual-fuel Engine Performance And Gas Supply System Optimization

Nowadays, the scarcity of oil resources and the environmental deterioration have been serious problems for human sustainable development. For the Compressed Natural Gas (CNG) has advantage in its abundant reserves and low exhaust emissions, it has become one of the most practical alternative fuel. In china, the Gasoline/CNG bi-fuel engines cost low and refits easily, are the most widely used in CNG vehicles. However, the bi-fuel engines generally have the problem of performance reduction.This paper bases on an electronic control multi-point injection gasoline engine, refits it as a bi-fuel engine. Then sets up a test bench and makes associated research. By adjusting control parameters and using fluid simulation software, in order to improve the performance of the bi-fuel engine, this study tests and optimizes the ignition advance angle and the fuel supply system. Meanwhile, analyzes the influencing factors in the test as well. The result in this paper possesses reference meaning in reducing the power loss of CNG engines and improving the refitting method of bi-fuel engines.The following works are completed in this paper:1. Analyzes the factors which affect the engines' performance, and the characteristic differences between CNG and gasoline. Confirms the main control objects in this test are the ignition advance angle and the gas supply system.2. Refits a gasoline engine as a bi-fuel engine, and sets up a test bench. The refitted engine has multi-points CNG injection. The ignition advance angle and the gas supply system could be adjusted as requirement.3. Based on the test result, concludes that the add-on intake manifold affects the original intake system, especially at high load and high speed.4. When using CNG as fuel, the ignition advance angle should be increased to the original angle. Comparing the results under different load and rotate speed, concludes that the proper increasing ignition advance angle for this engine is 12 degree.5. Based on the test result and theretical analysis, the gas supply pressure, nozzle diameter and injection pulse width in the gas supply system are the main factors for the CNG gas supply. By adjusting, theoretical caculating and computing with FLUENT software, confirms that to improve the engine's dynamic performance the optimized strategy is to properly increase the gas supply pressure, enlarge the diameter of nozzle and decrease the injection pulse width. The optimized result for this bi-fuel engine is 2.7mm nozzle diameter and 0.19MPa gas supply pressure. And the test indicated that this optimization scheme increase the engine's performance. After optimization the bi-fuel engine's dynamic performance using CNG increase from 75%-80% to 80%-85% of using gasoline.6. If the air-fuel ratio is proper, the emission of bi-fuel engine when using CNG ismuch lower than gasoline. The emission of HC reduces 10%-50%, the emission of CO reduces about 60%.