Towards Predicting Lean Blow-Off Based on Damköhler Number and Practical Reaction Zone

Lean Blow-off (LBO) is important in gas turbine combustion. In this paper, numerical simulation and experiment are conducted to develop a new method for LBO prediction of gas turbine combustors based on Damköhler (Da) number and practical reaction zone (PRZ). PRZ is established based on OH concentration in the reacting flow of combustor, and it is simplified to a perfectly stirred reactor (PSR) due to the drastic mixing caused by swirling flow. Flow time scale (Ft) and chemical time scale (Ct) contained in Da number are all specified based on PRZ. Flow time scale (Ft) is defined as the residence time of fuel flowing through the PRZ, and chemical time scale (Ct) is defined as the shortest time needed to trigger the chemical reaction in PRZ. Da numbers, which introduce the physical competition between Ft and Ct, are calculated under LBO conditions and design point. The average Da number at LBO is about 1, ranging from 0.6 to 1.86, and the Da number of design condition is 4.33, showing that the method proposed in the paper is reliable and has the potential for practical engineering applications.