缸内高压直喷天然气发动机燃烧过程数值研究
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摘要
以直喷天然气发动机为研究对象,基于正庚烷-甲烷化学动力学机理对发动机的燃烧过程进行了三维数值模拟,并对NO_x,CO和炭烟的排放趋势进行了预测。结果表明:对于缩口燃烧室,随着燃烧室凹坑深度的减小和燃烧室喉口直径的增大,天然气扩散燃烧火焰的传播速度越快,指示热效率越高。在燃烧室总深度相当的情况下,直口燃烧室形成的气流运动对天然气扩散火焰传播的促进作用小于缩口燃烧室,且对于直口燃烧室,采用较小的凹坑深度和较大的喉口直径不利于天然气在前期预混燃烧阶段的火焰传播,从而导致指示热效率的降低。采用缩口设计,减小燃烧室凹坑总深度和增大燃烧室凹坑的直径会导致NO_x排放的增加,但有利于CO和炭烟的控制。因此,对于高压直喷天然气发动机,采用缩口燃烧室设计有利于热效率和排放的兼顾,但是需要各个燃烧室尺寸的合理配合。
The 3 D numerical simulation of combustion process for a high pressure direct injection natural gas engine was conducted based on the chemical kinetics mechanism of n-heptane and methane and the trends of NO_x, CO and soot emissions were predicted. The results indicated that the total depth decrease and the throat diameter increase of reentrant combustion chamber could lead to an enhanced diffusion flame propagation of natural gas and higher indicated thermal efficiency. The flow motion of regular combustion chamber with the same depth had little effect on diffusion flame propagation of natural gas and the shallow bowl and large throat of combustion chamber was not helpful to flame propagation in the premixed combustion stage so that the indicated thermal efficiency decreased. The reentrant combustion chamber with shallow and narrow characteristics would lead to the higher NO_x emission, but achieved the lower CO and soot emissions. Accordingly, the reentrant combustion chamber with reasonable geometry parameters was beneficial to improve the thermal efficiency and emission.
The 3 D numerical simulation of combustion process for a high pressure direct injection natural gas engine was conducted based on the chemical kinetics mechanism of n-heptane and methane and the trends of NO_x, CO and soot emissions were predicted. The results indicated that the total depth decrease and the throat diameter increase of reentrant combustion chamber could lead to an enhanced diffusion flame propagation of natural gas and higher indicated thermal efficiency. The flow motion of regular combustion chamber with the same depth had little effect on diffusion flame propagation of natural gas and the shallow bowl and large throat of combustion chamber was not helpful to flame propagation in the premixed combustion stage so that the indicated thermal efficiency decreased. The reentrant combustion chamber with shallow and narrow characteristics would lead to the higher NO_x emission, but achieved the lower CO and soot emissions. Accordingly, the reentrant combustion chamber with reasonable geometry parameters was beneficial to improve the thermal efficiency and emission.
引文
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[2] Peterson M B,Barter G E,West T H,et al.A parametric study of light-duty natural gas vehicle competitiveness in the United States through 2050[J].Applied Energy,2014,125:206-217.
[3] Poompipatpong C,Cheenkachorn K.A modified diesel engine for natural gas operation:performance and emission tests[J].Energy,2011,36:6862-6866.
[4] Zhang Q,Xu Z,Li M,et al.Combustion and emissions of a Euro VI heavy-duty natural gas engine using EGR and TWC[J].Journal of Natural Gas Science and Engineering,2016,28:660-671.
[5] Ouellette P.High pressure injection of natural gas for diesel engine fueling[D].Vancouver:The University of British Columbia,1992.
[6] Christopher A L.Combustion of natural gas with entrained diesel in a heavy-duty compression-ignition engine[D].Vancouver:The University of British Columbia,2009.
[7] Mc Taggart-Cowan G P,Rogak S N,Munshi S R,et al.The influence of fuel composition on a heavy-duty,natural-gas direct-injection engine[J].Fuel,2010,89:752-759.
[8] Hill P G,Douville B.Analysis of combustion in diesel engines fueled by directly injected natural gas[J].Journal of Engineering for Gas Turbines and Power,2000,122:141-149.
[9] Jinn J.High Pressure Direct Injection[C].Colone: IANGV’,1998.
[10] Mc Taggart-Cowan G P.Injection parameter effects on a direct injected,pilot ignited,heavy duty natural gas engine with EGR[C].SAE Paper 2003-01-3089.
[11] Mc Taggart-Cowan G P,Bushe W K,Rogak S N,et al.PM and NOx reduction by injection parameter alterations in a direct injected,pilot ignited,heavy duty natural gas engine with EGR at various operating conditions[C].SAE Paper 2005-01-1733.
[12] Brown B S,Rogak S N,Munshi S.Multiple injection strategy in a direct injection natural gas engine with entrained diesel[C].SAE Paper 2009-01-1954.
[13] Mtui P.Pilot-ignited natural gas combustion in diesel engine[D].Vancouver:The University of British Columbia,1996.
[14] Munshi S R,Mc Taggart-Cowan G P,Huang J,et al.Development of a partially-premixed combustion strategy for a low emission,direct injection high efficiency natural gas engine[C]//Proceedings of the AMSE 2011 Internal Combustion Engine Division Fall Technical Conference.Mongantown:[s.n.],2011.
[15] Lee W G,Montgomery D.Numerical investigation of the performance of a high pressure direct injection (HPDI) natural gas engine[C]//In ASME 2014 Internal Combustion Engine Division Fall Technical Conference.Indiana:American Society of Mechanical Engineers,2014.
[16] Florea R,Neely G,Abidin Z,et al.Efficiency and Emissions Characteristics of Partially Premixed Dual-Fuel Combustion by Co-Direct Injection of NG and Diesel Fuel (DI2)[C].SAE Paper 2016-01-0779.
[17] Patel A,Kong S,Reitz R.Development and Validation of a Reduced Reaction Mechanism for HCCI Engine Simulations[C].SAE Paper 2004-01-0558.
[18] Metcalfe W K,Burke S M,Ahmed S S,et al.A Hierarchical and Comparative Kinetic Modeling Study of C1-C2 Hydrocarbon and Oxygenated Fuels[J].Intl. J. Chemical Kinetics,2013,45:638-675.