Matching of fuel injection and combustion systems for small swirl chamber diesel engine

Abstract: The huge annual output of single-cylinder diesel engines is a major feature of Chinese internal combustion engine industry. In China the amount of these engines with bore diameter below 80 mm accounts for 35% of domestic production. Most of these diesel engines adopt the swirl chamber combustion system. However, with the development of direct-injection process, many problems for these engines occur, such as large smoke emissions at full load, poor performance under low speed and high idle speed, and there are few basic researches on them. Therefore, the research of low-emission high-performance swirl chamber diesel engines contains certain academic significance and practical value. The 170F swirl chamber diesel engine was used as the research prototype, and with the method of experiment and numerical simulation, the fuel injection and combustion systems were analyzed. By the design of new injector, the establishment of simulation model of injection system and the optimization of the injection parameters, the maximum fuel pressure under the rated conditions increased from 18.54 to 25.28 MPa, the initial injection rate reduced and the shape of injection rate was optimized. By the simulation of combustion with the software FIRE, the deviate distance from the injection oil line to the center of the swirl chamber and the best volume ratio were determined. The results showed that when the deviate distance from the injection oil line to the center of the swirl chamber was at 0.33-0.38 R (R is the radius of the swirl chamber), and the volume ratio was in the range of 0.47-0.50, the mixing and combustion performance would be better. This study showed that in order to achieve the targets of low emissions and high performance, the injection parameters and performances of the swirl chamber diesel engine should be designed and optimized according to its displacement just similar with the direct-injection diesel engine. The test results of 170F swirl chamber diesel engine showed that the brake specific fuel consumption (BSFC) of the original engine under the rated condition (2.6 kW, 3 000 r/min) was 327.3 g/(kW·h) and the smoke was 4.5 BSU. When the long-size short-structure nozzle was used and the fuel injection system was optimized, the BSFC and the smoke decreased to 282.2 g/(kW·h) and 2.0 BSU respectively. After the parameters of the combustion system were matched, the BSFC and the smoke dropped to 274.7 g/(kW·h) and 1.2 BSU respectively. The experimental results showed that the specific emissions of the optimized diesel were lower than the emission standards in Phase Ⅲ in China. Compared with results of the original engine, the CO and HC+NOX emissions decreased by 70.3% and 20.9% respectively under the 5 conditions. Moreover, the CO and HC+NOX emissions decreased by 72.8% and 21.3% respectively under the 8 conditions. The BSFC decreased by 16% and the diesel smoke was reduced from 4.5 to 1.2 BSU under the rated condition. The research provides a technology route of energy-saving and emission-reduction for swirl chamber diesel engines.