非同步排气门正时对GDI汽油机缸内流场和工作性能的影响
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摘要
利用三维CFD软件建立了某1.5T缸内直喷汽油机的模型,分析比较了在2 000 r/min全负荷时非同步排气门正时策略下缸内流场、燃油雾化和燃烧过程变化的规律。结果表明:采用非同步排气门正时,缸内流场与原机有明显不同。湍流动能呈现"三峰"变化,缸内的平均湍流动能均大于原机(排气门1提前20°开启时变化最大);相比原机,缸内气体的平均流速有所增加,提高了燃油蒸发速率,上止点时缸内混合气更加均匀,但也会使得缸内的残余废气质量增大。排气门1提前20°开启时,缸内的燃烧速度比原机略快,缸内最高燃烧压力增加了0.3 MPa,但温度比原机略低,因此氮氧化物的排放低于原机,CO与原机持平。排气门1延迟20°开启效果不明显。综合考虑,排气门1提前20°开启能提升原机的动力性和排放性能。
The model of a 1.5 T gasoline direct injection engine was built with 3 D CFD software and the laws of in-cylinder flow field, fuel atomization and combustion process were compared and analyzed at full load of 2 000 r/min based on the asynchronous exhaust valve timing. The results showed that the flow field in the cylinder was different from that of the original engine when the non-synchronized exhaust valve timing strategy was adopted. The turbulent kinetic energy exhibited a characteristic of three peaks and its average value was greater than that of the original engine which had the greatest change when the exhaust valve 1 opened at the advance angle of 20°CA.Compared with the original engine, the average flow velocity of in-cylinder mixture increased, the fuel evaporation rate improved, the in-cylinder mixture on the top dead center became more uniform, but the residual gas increased. In addition, the in-cylinder combustion accelerated and the maximum pressure increased by 0.3 MPa.The in-cylinder temperature decreased and hence NO_x emission reduced, but CO emission kept the same. However, delaying the exhaust valve 1 by 20°CA would make no difference. Accordingly, advancing the exhaust valve 1 by 20°CA could improve the power and emission characteristics of the original engine.
The model of a 1.5 T gasoline direct injection engine was built with 3 D CFD software and the laws of in-cylinder flow field, fuel atomization and combustion process were compared and analyzed at full load of 2 000 r/min based on the asynchronous exhaust valve timing. The results showed that the flow field in the cylinder was different from that of the original engine when the non-synchronized exhaust valve timing strategy was adopted. The turbulent kinetic energy exhibited a characteristic of three peaks and its average value was greater than that of the original engine which had the greatest change when the exhaust valve 1 opened at the advance angle of 20°CA.Compared with the original engine, the average flow velocity of in-cylinder mixture increased, the fuel evaporation rate improved, the in-cylinder mixture on the top dead center became more uniform, but the residual gas increased. In addition, the in-cylinder combustion accelerated and the maximum pressure increased by 0.3 MPa.The in-cylinder temperature decreased and hence NO_x emission reduced, but CO emission kept the same. However, delaying the exhaust valve 1 by 20°CA would make no difference. Accordingly, advancing the exhaust valve 1 by 20°CA could improve the power and emission characteristics of the original engine.
引文
[1] Kirwan J E, Shost M, Roth G, et al. 3-cylinder turbocharged gasoline direct injection: a high value solution for low CO2 and NOx emissions[C].SAE Paper 2010-01-0590.
[2] 于秀敏,王野,李盛成,等.直喷比例对双喷射汽油机燃烧和排放影响的试验研究[J].汽车工程,2017,39(9):989-996.
[3] Williams A M,Baker A T,Garner C P.Turbo-discharging: predicted improvements in engine fuel economy and performance[C].SAE Paper 2011-01-0371.
[4] Sideris M,Boye M,D?ring M,et al.Innovation trends in the field of internal combustion engines[C].SAE Paper 2009-01-1944.
[5] Kleeberg H,Tomazic D,Lang O,et al.Future potential and development methods for high output turbocharged direct injected gasoline engines[C].SAE Paper 2006-01-0046.
[6] 尹丛勃,张振东,郭辉,等.可变涡流对直喷汽油机进气流动和油气混合特性影响的数值模拟[J].汽车工程,2013,35(8):677-682.
[7] Han S,Qin J,Lin M,et al.Simulation study of injection strategy and tumble effect on the mixture formation and spray impingement in a gasoline direct injection engine[C].SAE Paper 2014-01-1129.
[8] 刘国庆,舒歌群,朱航,等.滚流和挤气对汽油机燃烧和性能影响[J].内燃机学报,2011,29(4):307-312.
[9] 李之华.进气门和喷油对直喷汽油机混合气和燃烧控制的模拟研究[D].天津:天津大学,2012.
[10] 刘凯敏,杨靖,邓帮林,等.非同步气门正时对高速汽油机进气及燃烧过程的影响[J].内燃机工程,2016,37(2):94-100.
[11] 李相超.先进直喷汽油机喷嘴选型与匹配技术研究[D].上海:上海交通大学,2012.
[12] Montanaro A,Malaguti S,Alfuso S.Wall impingement process of a multi-hole GDI spray:experimental and numerical investigation [J].Journal of Pharmaceutical & Biomedical Analysis,2012,22(2):393-402.
[2] 于秀敏,王野,李盛成,等.直喷比例对双喷射汽油机燃烧和排放影响的试验研究[J].汽车工程,2017,39(9):989-996.
[3] Williams A M,Baker A T,Garner C P.Turbo-discharging: predicted improvements in engine fuel economy and performance[C].SAE Paper 2011-01-0371.
[4] Sideris M,Boye M,D?ring M,et al.Innovation trends in the field of internal combustion engines[C].SAE Paper 2009-01-1944.
[5] Kleeberg H,Tomazic D,Lang O,et al.Future potential and development methods for high output turbocharged direct injected gasoline engines[C].SAE Paper 2006-01-0046.
[6] 尹丛勃,张振东,郭辉,等.可变涡流对直喷汽油机进气流动和油气混合特性影响的数值模拟[J].汽车工程,2013,35(8):677-682.
[7] Han S,Qin J,Lin M,et al.Simulation study of injection strategy and tumble effect on the mixture formation and spray impingement in a gasoline direct injection engine[C].SAE Paper 2014-01-1129.
[8] 刘国庆,舒歌群,朱航,等.滚流和挤气对汽油机燃烧和性能影响[J].内燃机学报,2011,29(4):307-312.
[9] 李之华.进气门和喷油对直喷汽油机混合气和燃烧控制的模拟研究[D].天津:天津大学,2012.
[10] 刘凯敏,杨靖,邓帮林,等.非同步气门正时对高速汽油机进气及燃烧过程的影响[J].内燃机工程,2016,37(2):94-100.
[11] 李相超.先进直喷汽油机喷嘴选型与匹配技术研究[D].上海:上海交通大学,2012.
[12] Montanaro A,Malaguti S,Alfuso S.Wall impingement process of a multi-hole GDI spray:experimental and numerical investigation [J].Journal of Pharmaceutical & Biomedical Analysis,2012,22(2):393-402.