Acting mechanism of low ambient temperature on wall-impinging diesel spray ignition at an extensive range. (15th November 2021)

• Record Type: Journal Article
• Authors: Li, Yaozong; Li, Xiangrong; Cao, Weiren; Shi, Zhicheng; Bo, Yaqing; Wu, Han
• Is Part Of: Fuel. Volume 304(2021)
• Publication Date: 2021-11-15
• Subjects: Low temperature -- Spray impingement -- Wall cooling -- Fuel-air mixing -- Flame evolution -- Ignition mechanism; Fuel -- Periodicals; Coal -- Periodicals; Coal; Fuel; Periodicals; 662.6
• DOI: 10.1016/j.fuel.2021.121344
• Languages: English
• ISSNs: 0016-2361

Abstract

Highlights: The fuel adhesion ratio increases linearly as the ambient temperature decreases. Cold wall has little effect on fuel–air mixing and ignition at high temperatures. Cold wall causes evaporation and fuel fraction to decrease at low temperatures. Competition between reaction and diffusion lead to four different ignition modes. Ignition threshold of impinging spray increases by 40 K compared with free jet. Abstract: The impinging spray ignition has been widely studied, but the mechanism is unclear, especially at low temperatures. Thus, the 3-D simulation was conducted at ambient temperatures of 740–1200 K and wall temperature of 393 K. The results reveal that the fuel–air mixing and ignition processes of an impinging jet are approximately the same as that of a free jet at 1000–1200 K. However, as the temperature decreases, the attached fuel mass increases linearly, and the adhesion ratio is only 4.5% at 1000 K but as high as 32.6% at 780 K. The wall cooling causes the evaporation rate to drop sharply, thus the fuel mass fraction suitable for autoignition decreases. With the decrease of ambient temperature, the maximum temperature after cool flame decreases linearly, and the transition time from cool to hot flames is greatly extended. Compared to free jet, the heat release of impinging jet decreases significantly, and the ignition threshold increases by 40 K. The competition between chemical reaction and fuel diffusion rate divides the impinging ignition into four different modes: (1) The flame initially occurs at the center and then spreads to the edge. (2) The hot flame at the edge spreads to the center. (3) The hot flame spreads to the center but the central region misfires. (4) Only cool flame is observed at the edge. At low temperatures, most of the fuel film remains. At 900 K, 34.4% of the fuel film participates in combustion, but at 780 K it is reduced to 6.6%.