Suppression of flame instability by a short catalytic segment on the wall of a micro channel with a prescribed wall temperature profile. (15th December 2018)

• Record Type: Journal Article
• Authors: Wang, Shixuan; Li, Linhong; Fan, Aiwu
• Is Part Of: Fuel. Volume 234(2018)
• Page Start: 1329
• Page End: 1336
• Publication Date: 2018-12-15
• Subjects: Micro combustion -- Flame instability -- Catalytic segment -- Heterogeneous reaction -- Local burning velocity; Fuel -- Periodicals; Coal -- Periodicals; Coal; Fuel; Periodicals; 662.6
• DOI: 10.1016/j.fuel.2018.08.025
• Languages: English
• ISSNs: 0016-2361

Abstract

Graphical abstract: This graph schematically illustrates that in the micro flow reactor with a prescribed temperature profile, the flame instability of repetitive extinction and ignition can be suppressed and a stable flame can be achieved if there is a 3-mm Pt segment located at x = 49–52 mm on the inner surface. Highlights: The effect of catalyst location on flame stability was numerically investigated. Flame stability in a microchannel was improved by a Pt segment at suitable locations. The catalytic segment consumes some reactants and reduces flame propagation speed. In the presence of a Pt segment, the flame is constrained to farther downstream. Abstract: Flame with repetitive extinction and ignition (FREI) has received extensive attention since it was first observed in a heated micro channel of 80-mm long. However, how to suppress it was seldom reported to date. In this study, we imposed a 3-mm Platinum (Pt) segment on the channel wall to improve the FREI instability. Two dimensional numerical investigation with detailed gas phase/catalytic reaction mechanisms of CH4 /air mixture was performed at Vin = 25 cm/s and ϕ = 0.85. The results demonstrate that when the catalyst is set at x = 48–51 mm, FREI transforms into a pulsating mode. As the Pt segment is shifted to x = 49–52 mm, flame pulsating is completely suppressed and transforms into a stable flame. These facts manifest that flame instability can be effectively improved by a short Pt segment located at a suitable position. Analysis reveals that the Pt surface consumes some amount of CH4 and O2 in advance. Moreover, the adsorption of intermediate species grows stronger when flame propagates upstream. As a result, the burning velocity of gas phase combustion is reduced and flame propagation range is restricted to the downstream of catalyst where the wall temperature is relatively high. Hence, flame quenching can be avoided. When the catalyst is located at x = 49–52 mm, the impact of catalytic reaction becomes more pronounced and the flame propagation range is constrained to farther downstream with higher wall temperature. Therefore, flame can be hopefully stabilized at a certain position in the end.