Cyclic flame propagation in premixed combustion

Abstract

In experiments of hot surface ignition and subsequent flame propagation, a puffing flame instability is observed in mixtures that are stagnant and premixed prior to ignition. By varying the size of the hot surface, power input, and combustion vessel volume, it was determined that the instability is a function of the interaction of the flame, with the fluid flow induced by the combustion products rather than the initial plume established by the hot surface. Pressure ranges from 25 to 100 kPa and mixtures of n-hexane/air with equivalence ratios between φ = 0.58 and 3.0 at room temperature were investigated. Equivalence ratios between φ = 2.15 and 2.5 exhibited multiple flame and equivalence ratios above φ = 2.5 resulted in puffing flames at atmospheric pressure. The phenomenon is accurately reproduced in numerical simulations and a detailed flow field analysis revealed competition between the inflow velocity at the base of the flame and the flame propagation speed. The increasing inflow velocity, which exceeds the flame propagation speed, is ultimately responsible for creating a puff. The puff is then accelerated upward, allowing for the creation of the subsequent instabilities. The frequency of the puff is proportional to the gravitational acceleration and inversely proportional to the flame speed. A scaling relationship describes the dependence of the frequency on gravitational acceleration, hot surface diameter, and flame speed. This relation shows good agreement for rich n-hexane/air and lean hydrogen/air flames, as well as lean hexane/hydrogen/air mixtures.

Experimental and numerical study of the ignition of hydrogen-air mixtures by a localized stationary hot surface

“…The present study focuses on a stationary localized surface with an imposed heating rate. Similar configurations were studied by Roth et al [7,8], Beyer and Markus [9], Dubaniewicz [10], Dubaniewicz et al [11], Dubaniewicz et al [3], Bothe et al [12], Homan [13], Boettcher et al [14], Boettcher [15], and Menon et al [16]. These previous studies demonstrated the importance of the mixture chemical properties and surface properties (e.g.…”

“…The ignition experiments were performed in a closed vessel with a volume of 2.2 L. This combustion facility has been previously described in detail by Boettcher et al [14], Boettcher [15] and Menon et al [16]. Briefly, the vessel inner dimensions were 114 mm x 114 mm x 171 mm.…”

Ignition of fuel–air mixtures from a hot circular cylinder

“…The uniformity of surface temperature needs to be optimized and quantified to reduce uncertainties. The present study extends previous work that used a commercial glow plug as a hot surface [34][35][36][37][38][39] . To improve the surface temperature uniformity, a new cylindrical surface was developed with a unity aspect ratio of the hot surface section.…”

“…Figure 1 presents a cross-sectional view of the device. The material, stainless steel (316), corresponds to previous work using a commercial glow plug as a hot surface [34][35][36][37]39] . The stainless steel tube was centered between two 30 mm long thermally and electrically insulating quartz glass tubes to create a continuous geometric contour and to limit axial heat loss.…”

Oxidation of n-hexane in the vicinity of the auto-ignition temperature

“…Accidental combustion events in fuel tanks and flammable leakage zone is a major concern in aviation safety [1,2,3,4]. For example, the National Transport Safety Board investigation pointed out that the explosion of the center wing fuel tank resulting from the ignition of the flammable atmosphere in the tank as the probable cause of the flight TWA 800 accident in 1996 [5].…”