Ignition and stabilization of laminar premixed n-heptane/air flames under engine-like conditions

被引:6
作者
Zhao, Wanhui [1 ]
Sun, Ting [2 ]
Liu, Shuqi [2 ]
Zhong, Lijia [2 ]
Zhang, Xiaojun [2 ]
Zhou, Lei [2 ]
Wei, Haiqiao [2 ]
机构
[1] Civil Aviat Univ China, Coll Aeronaut Engn, Tianjin 300300, Peoples R China
[2] Tianjin Univ, State Key Lab Engines, Tianjin 300072, Peoples R China
基金
中国国家自然科学基金;
关键词
Double-flame structure; Cool flame; Autoignition; Stabilization; COOL FLAMES; JET FLAMES; ELEVATED-TEMPERATURES; AUTO-IGNITION; WARM FLAMES; PROPAGATION; COMBUSTION; MIXTURE; EVOLUTION; SPEEDS;
D O I
10.1016/j.fuel.2023.128035
中图分类号
TE [石油、天然气工业]; TK [能源与动力工程];
学科分类号
0807 ; 0820 ;
摘要
The multi-stage ignition process of a laminar premixed n-heptane/air mixture is investigated under engine -relevant conditions. The cold fuel/air mixture is injected into a hot environment through an inflow boundary at different inlet velocities. Results show that a double-flame structure for stoichiometric mixture is observed and it transitions to a single flame at an inlet temperature (TFuel) of 700 K. The cool flame is stabilized near the inlet for the case with TFuel = 900 K before the hot flame merging with it. However, both the cool and hot flames move upstream for TFuel = 800 K due to the negative temperature coefficient (NTC) behavior. In addition, the effect of inlet velocity is also studied. By increasing the inlet velocity, the hot flame becomes lifted off. Comparisons of the ignition Damkohler number (Daign) defined by the ratio of the residence time to the cool-or hot-flame IDTs illustrate the different controlling mechanisms. At a low temperature of 700 K, both low-temperature combustion (LTC) and high-temperature combustion (HTC) have a Daign value of unity, indicating that the stabilization process is mainly controlled by autoignition rather than diffusion. The heating effect from the hot environment enhances the NTC characteristics of the premixed flame, thus, shortening the IDT. Whereas at 800 K, the value of Daign for the LTC is of unity, but that of HTC decreases, especially at a low inlet velocity, indicating that diffusion plays a more important role for HTC and the flame is stabilized by propagation, which can also be confirmed from the comparisons of the 0-D and 1-D ignition delay times (IDTs). Diffusion of intermediate radicals and heat suppresses the appearance of the high-temperature ignition at an inlet velocity of 1 m/s. At 900 K, high inlet velocity can increase the Daign to unity, indicating a transition in the combustion regime from propagation to autoignition.
引用
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页数:10
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