二甲醚对甲烷稀混合气燃烧过程影响的可视化研究
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摘要
在一台安装有进气道喷射甲烷和缸内直喷二甲醚(DME)的单缸光学发动机上,研究了DME喷射时刻对甲烷空气稀混合气压缩着火燃烧过程和火焰发展过程的影响。结果表明:在直喷DME下,气缸内的燃烧放热过程主要受到DME直喷时刻的控制。在-60°～-40°喷射DME时,放热率曲线呈单峰,在-30°～-15°喷射DME时,放热率曲线呈两阶段放热特征。气缸内的燃烧呈现自燃+火焰传播的特征。此外,DME喷射时刻还影响着火点的位置。随着DME喷射时刻的推迟,着火区域分布更加集中。与火花点燃甲烷燃烧相比,在压缩着火方式下,直喷DME能大幅提高甲烷/空气混合气燃烧初期的火焰传播速度,使燃烧放热过程加快。
The effect of DME injection timing on the compression ignition and flame development of lean methane-air mixture was studied on a single cylinder optical engine equipped with port methane injection and in-cylinder DME direct injection.Results show that in the case of DME direct injection,the combustion process in the cylinder is mainly controlled by DME injection timing.When the DME injection timing is in the range of 40°to 60°BTDC,the heat release rate curve shows a unimodal distribution and a bimodal distribution in the range of 15°to 30°BTDC.At this time,the in-cylinder combustion of DME/methane/air mixture shows the characteristics of self-ignition and flame propagation.Moreover,the DME injection timing also influences the location of ignition point.With the delay of DME injection timing,the distribution of ignition zone is more concentrated.Compared with port methane injection with spark ignition,under compression ignition conditions,the DME direct injection can significantly increase the flame propagation speed of methane-air mixture in the early stage of combustion,thus accelerating the combustion process.
The effect of DME injection timing on the compression ignition and flame development of lean methane-air mixture was studied on a single cylinder optical engine equipped with port methane injection and in-cylinder DME direct injection.Results show that in the case of DME direct injection,the combustion process in the cylinder is mainly controlled by DME injection timing.When the DME injection timing is in the range of 40°to 60°BTDC,the heat release rate curve shows a unimodal distribution and a bimodal distribution in the range of 15°to 30°BTDC.At this time,the in-cylinder combustion of DME/methane/air mixture shows the characteristics of self-ignition and flame propagation.Moreover,the DME injection timing also influences the location of ignition point.With the delay of DME injection timing,the distribution of ignition zone is more concentrated.Compared with port methane injection with spark ignition,under compression ignition conditions,the DME direct injection can significantly increase the flame propagation speed of methane-air mixture in the early stage of combustion,thus accelerating the combustion process.
引文
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[4]李伟峰.高稀释-预混合天然气发动机燃烧过程分析与优化[D].吉林:吉林大学,2016.
[5]YANG L P,SONG E Z,DING S L,et al.Analysis of the dynamic characteristics of combustion instabilities in a premixed lean-burn natural gas engine[J].Applied Energy,2016,183:746-759.
[6]WEI L J,GENG P.A review on natural gas/diesel dual fuel combustion,emissions and performance[J].Fuel Processing Technology,2016,142:264-278.
[7]YANG B,WANG L,NING L,et al.Effects of pilot injection timing on the combustion noise and particle emissions of a diesel/natural gas dual-fuel engine at low load[J].Applied Thermal Engineering,2016,102:822-828.
[8]陈朝阳,巩静,黄佐华,等.二甲醚/空气/稀释气层流燃烧特性研究[J].内燃机工程,2014,35(3):32-37.CHEN Z Y,GONG J,HUANG Z H,et al.Study on premixed stratified combustion characteristics of DME/air/diluent[J].Chinese Internal Combustion Engine Engineering,2014,35(3):32-37.
[9]FU X Q,HE B Q,LI H T,et al.Effect of direct injection dimethyl ether on the micro-flame ignited(MFI)hybrid combustion and emission characteristics of a 4-stroke gasoline engine[J].Fuel Processing Technology,2018,167:555-562.
[10]ZHANG H F,SEO K,ZHAO H,Combustion and emission analysis of the direct DME injection enabled and controlled auto-ignition gasoline combustion engine operation[J].Fuel,2013,107:800-814.
[11]徐思鹏,何邦全,付雪青,等.直喷二甲醚对稀汽油混合气燃烧过程影响的研究[J].内燃机工程,2018,39(4):67-72.XU S P,HE B Q,FU X Q,et al.Effect of DME direct injection on the combustion processes of lean gasoline xixture in an engine[J].Chinese Internal Combustion Engine Engineering,2018,39(4):67-72.
[12]PUTRASARI Y,JAMSRAN N,LIM O.An investigation on the DME HCCI autoignition under EGR and boosted operation[J].Fuel,2017,200:447-457.
[13]KONG S C.A study of natural gas/DME combustion in HCCIengines using CFD with detailed chemical kinetics[J].Fuel,2007,86:1483-1489.
[14]LEE S,JEONG S,LIM O.An investigation on the spray characteristics of DME with variation of ambient pressure using the common rail fuel injection system[J].Journal of Mechanical Science&Technology,2012,26(10):3323-3330.
[15]王建昕,帅石金.汽车发动机原理[M].北京:清华大学出版社,2011.
[16]XIE H,XU K,CHEN T,et al.Investigations into the influence of dimethyl ether(DME)micro flame ignition on the combustion and cyclic variation characteristics of flame propagation-auto-ignition hybrid combustion in an optical engine[J].Combustion Science and Technology,2017,189(3):453-477.
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