Design of a Numerical Microcombustor for Diffusion Flames

• Published in: Combustion science and technology Vol. 184; no. 7-8; pp. 1121 - 1134
• Main Authors: Badra, J., Masri, A. R.
• Format: Journal Article
• Language: English
• Published: Philadelphia, PA Taylor & Francis Group 01.07.2012; Taylor & Francis; Taylor & Francis Ltd
• Subjects: Applied sciences; Combustion. Flame; Conductivity; Diffusion; Diffusion flame; Energy; Energy. Thermal use of fuels; Exact sciences and technology; Flame stability; Heat transfer; Industrial design; Industrial equipment; Methane; Microcombustion; Micromixing; Reaction kinetics; Theoretical studies. Data and constants. Metering; Thermal quenching; Methane; Mixing; Stability; Thermal quenching; Flame stability; Combustion; Flame propagation; Quenching; Micromixing; Combustion chamber; Diffusion flame; Flame structure; Thermal conductivity; Microcombustion; Burner; Kinetics; Strength; Heat transfer
• ISSN: 0010-2202; 1563-521X
• DOI: 10.1080/00102202.2012.664003

This article focuses on the development of a numerical microcombustor capable of stabilizing a diffusion flame of methane. Different designs are tested with the objective of optimizing mixing of the methane and air streams. Stability of the flame is then ensured by increasing the temperature of the incoming streams of reactants and changing the internal conductivity of the combustor material with and without allowing heat transfer to the surrounding. Two-dimensional (2D) as well as three-dimensional (3D) computations of the microreactor are presented using detailed chemical kinetics. It was found that the optimal design that ensures adequate mixing requires the presence of a restriction at the inlet of the combustion chamber forcing the incoming streams to converge while introducing minor pressure drop. A flame could not be sustained in an adiabatic microreactor for mixtures entering at ambient temperature (27°C), but stability was achieved at inlet temperatures of 100°C and 300°C. When heat is allowed to transfer from the products to the reactants, while keeping the microburner externally adiabatic, stronger and more stable flames were observed within the domain and the strength of the flame increases with decreasing the thermal conductivity of the walls. Calculations in 3D were carried out on a scaled-up version of the domain to demonstrate the effects of thermal conductivity and gap size (distance between the two plates that constrain the burner). Such calculations provide useful information that assist in the construction of a physical microreactor.