Flame front stability of low calorific fuel gas combustion with preheated air in a porous burner

Increasing stringent rules on carbon emissions have led to the development of more efficient combustion technology. For instance, the development of porous media combustion has overcome the drawbacks experienced in the traditional combustion systems and they can be used both in combusting premixed gas fuel and air, liquid fuel, and solid fuel. Combustion in porous media have been classified into filtration and steady combustion depending on flame stability. In a recently published literature, the flammability limit has been identified as a significant consideration factor in the application of porous media combustion thereby attracting significant attention of researchers.

To this end, various burners have been developed for both domestic and industrial applications. However, for stable and safe operation of the burner, several factors including enhancing the flame stability must be considered. Presently, flame stabilization has been studied using numerical, analytical and experimental methods. Unfortunately, obtaining a stable flame in the porous burners have remained a great challenge.

Among the available methods for obtaining stable flames in the porous burner, using a two-layer structure have been used to efficiently stabilize the interface at the porous media. Whereas most of the available methods have adopted the packed particle burners, adoption of ceramic foam burners for flame stabilization still remains a research area. Additionally, recent research work has not focused much on the effects of the preheated air temperature on the flame front stability and particularly for ceramic foam burners.

To this note, Dr. Guanqing Wang, Pengbo Tang, Dr. Yuan Li, Professor Jiangrong Xu at Hangzhou Dianzi University in collaboration with Professor Franz Durst from FMP Technology GmbH investigated the flame front stabilization of low calorific fuel gas combustion. In particular, the combustion involved a preheated air in a burner filled with aluminum oxide ceramic foams. The obtained results at room temperature were compared to the corresponding experimental results to validate the feasibility of the numerical method. The work is currently published in the journal, Energy.

Briefly, the authors developed a two-dimensional model to simulate the flame propagation process and investigate the flame front stability, particularly for ultra-lean combustion. Next, the flame front inclination, the propagation velocity and wall heat loss were analyzed to determine the effects of the preheated air temperature.

The authors recorded a good agreement between the flame front instability at room temperature and the corresponding experimental results. Additionally, the flame stabilization in low calorific fuel gas combustion was enhanced by an increase in the preheated air temperature. However, the temperature loses through the wall significantly enhanced the flame front inclination with little effect on the propagation velocity.

In summary, the research team successfully achieved super-adiabatic combustion for low calorific fuel gas combustion comprising of preheated air in the ceramic foam burner. In general, the air was preheated to a critical temperature to obtain a stable combustion flame. The stability of the flame decreased with the increase in the equivalence ratio and the decrease in the inlet velocity. The study provides vital new results that will pave the way for clean combustion of low calorific fuel gas in porous media.