| With sharp increase of car ownership in China, the pollution caused by internal engine exhaust gets more attention. The traditional internal engine, restricted by combustion mode, is facing many problems. For example, the CI diesel engine with high NOx and PM emission needs complex after-treatment devices to meet emission regulations; the SI gasoline engine has a poor fuel economy because of lower thermal efficiency. Therefore, finding a new combustion mode with high efficiency and low emission becomes crucial to the sustainable development of internal engine industry.Homogeneous charge induced ignition, which is featured by pre-mixed and lean burn, has high efficiency and low emission at the same time. It’s a new combustion mode with giant application potential. In this paper, a research on homogeneous charge induced ignition at low temperature(LT-HCII) with gasoline-diesel dual fuel is conducted through experiment. The major job has double parts. First, the effects of gasoline ratio, diesel injecting time, EGR ratio and diesel rail pressure on engine performance and emission were studied in detail. Second, emission decrease caused by DOC and highly pre-mixed diesel was also researched deeply. The whole experiment was conducted on a six-cylinder diesel engine. Also, gasoline injecting and open control systems have been adapted to meet experimental requirements. Finally, rail pressure, EGR ratio, injecting time, pulse and number could be adjusted flexibly.Results show that LT-HCII can reach quite high indicated thermal efficiency, nearly equal to the level of CI diesel engine. However, the combustion efficiency decreases due to the increase of THC and CO emission. With the increase of gasoline ratio, proportion of pre-mixed combustion enlarges, the shape of heat release rate curve changes from double peaks to single. The emission of NOx and Soot decreases simultaneously without trade-off relationship, indicating that low temperature combustion appears. At 90% gasoline ratio, NOx decreases to 0.79g/(kW·h) and Soot emission nearly zero, however, COV is within 2%, showing that just a little induced diesel can control the combustion phase well. Advancing diesel injecting time is an effective method to improve combustion efficiency, lower THC and CO emission. But it causes the problem of engine operation roughness. With diesel injecting time advancing, Soot emission remains at extremely low level all the while, showing that gasoline ratio is the key point to decrease Soot emission. The combustion of dilute gasoline homogeneous charge is improved with appropriate EGR ratio, then, gasoline pre-mixed combustion speeds up, diesel diffusive combustion slows down, both combustion and indicated thermal efficiency rise. NOx emission decreases and Soot emission keeps unchanged with the increase of EGR ratio, the max value of smoke opacity is only 0.036m-1, showing that LT-HCII is insensitive to EGR ratio, it can reach extremely low NOx and Soot emission simultaneously with large EGR ratio. Enlarging diesel rail pressure can bring the effect of THC and CO emission decrease, COV lower and indicated thermal efficiency increase, however, it causes the problem of combustion temperature and NOx emission rise. When the diesel rail pressure uses 60MPa in LT-HCII, the smoke opacity is only 0.036m-1, but it needs 140MPa to reach same level in pure diesel mode, showing that LT-HCII can use lower rail pressure to meet the regulation of Soot emission.Besides, DOC doesn’t have obvious influence on combustion characteristic and the transformation efficiency of THC and CO is over 90%. With DOC, both THC and CO can meet Euro v emission regulation, so it solves the problem of high incomplete combustion products exhaust in LT-HCII. Meanwhile, highly pre-mixed diesel can improve NOx and Soot emission in medium and small load effectively. Within the experimental condition, NOx could decrease to 0.39g/(kW·h) and the smoke opacity is only 0.0012m’1 at this moment. |
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