Experimental Study On An Electronically Controlled Injection Dedicated NG Car Engine

In this study, experimental investigations were carried out on a natural gas (NG) engine for 1.3L passenger vehicles, in order to explore the influence of spark advance angle, excessive air ratio, and compression ratio on the engine characteristics, such as combustion, dynamic, economy and emissions. Besides, a specialized three-way catalyst converter for NG engine was developed, considering the severe feature of this alternative fuel with high emission of unburned methane (CH4). The experimental results for the engine with compression ratio of 10 were achieved and analyzed, drawing several conclusions as follows.The maximum brake pressure would be boosted and its time would occur in advance, when the spark advance angle was increased. Meanwhile, the curve for heat release rate moved forward to the top dead center (TDC) and the peak value was improved drastically. Besides, the advance of spark angle would reduce the coefficient of variation (CoV) evidently. The flame development period was extended while the rapid burn period was shortened, though the whole combustion period was maintained basically. Increasing the excessive air ratio would boost the maximum brake pressure while have little effect on heat release rate. However, the CoV would be increased at this time. And all of the periods for flame development, rapid burn and whole combustion were prolonged.For a given spark advance angle, all the optimal specific gas consumptions for different loads were achieved at the excessive air ratio of 1.2. The fuel economy would be deteriorated when the excessive air ratio was over 1.4. The specific gas consumption was significantly influenced by the spark advance angle, especially at low load. Therefore, it is extremely necessary to optimize the spark advance angle to improve the fuel economy. In terms of emissions, both of CO and NMHC would decrease as the increase of excessive air ratio. However, NOx would increase at first and then decrease later, while THC and CH4 presented opposite tendencies to that of NOx. Increasing the spark advance angle would lead to deteriorations for all the emissions above.The pistons were changed to increase the compression ratio up to 12 from 10, and the same experiments were conducted in the modified engine to compare the performances between the two different compression ratios. It was revealed from the results that the brake pressure was increased slightly, the peak value of heat release rate was increased 10% and the dynamic property was improved 15% at the higher compression ratio. The CoV was decreased. And the boundary of excessive air ratio for lean burn could be extended from 1.4 to 1.5 at 0.5 MPa for 2800 rpm. The specific gas consumption would be reduced obviously. All of the periods for flame development, rapid burn and whole combustion were also reduced by different degrees. Besides, the emission of CO was improved largely by increasing the compression ratio, though NOx and THC increased slightly. A mapping characteristics chart was achieved through calibrating the ECU for the modified NG engine. It was shown that the mean brake effective pressure (BMEP) reached up to 1.1 MPa. The minimum specific gas consumption decreased down to 200 g/(kW?h) , which was improved distinctly compared to 220 g/(kW?h) for the engine with compression ratio of 10, and the economical operation scope was also extended largely.Specialized three-way catalyst converters were developed for the NG engine, and the optimal one was obtained by experimental comparisons. It was suggested that the specialized catalyst could reduce the emissions of CO HC and NOx largely.