LES/TPDF investigation of the effects of ambient methanol concentration on pilot fuel ignition characteristics and reaction front structures

FUEL

卷:287

Article

Xu, Shijie¹  Pang, Kar Mun²  Li, Yaopeng^1,3  Hadadpour, Ahmad¹  Yu, Senbin¹  Zhong, Shenghui^1,4  Jangi, Mehdi⁵  Bai, Xue-song¹ 

[1] Lund Univ, Dept Energy Sci, S-22100 Lund, Sweden

[2] Teglholmsgade41, MAN Energy Solut, DK-2450 Copenhagen SV, Denmark

[3] Dalian Univ Technol, Minist Educ, Key Lab Ocean Energy Utilizat & Energy Conservat, Dalian 116024, Peoples R China

[4] Tianjin Univ, State Key Lab Engines, 135 Yaguan Rd, Tianjin 300350, Peoples R China

[5] Univ Birmingham, Sch Mech Engn, Birmingham B15 2TT, W Midlands, England

关键词: Dual-fuel combustion;    Auto-ignition;    Engine Combustion Network;    Large eddy simulation;    Eulerian stochastic field;   

DOI  :  10.1016/j.fuel.2020.119502

来源: Elsevier

【 摘 要 】

Large-eddy simulations with a transported probability density function model coupled with a finite-rate chemistry is applied to study the ignition process of an n-heptane spray in a constant volume chamber with a premixed methanol-air atmosphere under conditions relevant to reactivity controlled compression ignition (RCCI) engines. Three reacting spray cases with initial methanol-air equivalence ratio (phi(m)) ranging from 0 to 0.3 are investigated at an initial temperature of 900 K. The case setup is based on the Engine Combustion Network Spray-H configuration, where n-heptane fuel is used. The effects of the ambient methanol-air equivalence ratio on the ignition characteristics and the reaction front structures in n-heptane/methanol RCCI combustion are studied in detail. It is found that the ambient methanol affects the low temperature chemistry of n-heptane, which results in a change of spatial distribution of key species such as heptyl-peroxide, and therefore the cool flame structure. With the presence of methanol in the ambient mixture cool flame is found in the entire fuel-rich region of the n-heptane jet, while when methanol is absent in the ambient mixture, the cool flame is established only around the stoichiometric mixture close to the n-heptane injector nozzle. In general, both lowand high-temperature ignition stages of n-heptane ignition are retarded by the methanol chemistry. An increase in phi m leads to a decrease of the peak heat release rate of the n-heptane first-stage ignition. The chemistry of methanol inhibits the n-heptane ignition by decreasing the overall hydroxyl radicals (OH) formation rate and reducing the OH concentration during the transition period from the first-stage ignition to the second-stage ignition. As a result, the transition time between the two ignition stages is prolonged. Under the present lean methanol/air ambient mixture conditions, the impact of methanol on n-heptane ignition has a tendency of reducing the high temperature, fuel-rich region, which is in favor of soot reduction.

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