(619d) Simulation Study of Microburners with Spatial Catalyst Structuring

The objective of this work is to study the effect of spatial catalyst structuring on the steady state performance and ignition behavior of lean propane combustion in Platinum catalyzed microburners. While homogeneous combustion in microburners is susceptible to thermal and radical quenching, catalytic combustion benefits from the high (catalytic) surface area and fast mass transfer rates existing in microburners. During startup, ignition is achieved by preheating the fuel/air mixture above the so-called ignition temperature. During the ignition phase, reactants are unconverted, resulting in large emissions. Moreover, a desirable property of microburners used for portable power generation is that they should be fast-starting.

In our earlier work, we investigated steady state behavior and stability of Pt-catalyzed microburners [1] and ignition from cold-start conditions [2]. We showed that selectively heating the initial section of the micro-burner to promote front-end ignition reduced the power required for ignition [2]. In past, catalyst segmentation has been used to improve product selectivity [3] or to reduce the catalyst cost [4]. In this work, we study the effect of spatial catalyst structuring on the transient ignition behaviour of propane/air combustion in Pt-catalyzed microburners.

Simulations performed with in-house codes show certain advantages of catalyst segmentation on microburner performance, compared to the case when the entire microburner is catalytic. However, the in-house code does not adequately capture the enhanced heat and mass transfer observed at boundaries of catalytic segments (arising due to singularities at these boundaries). Hence, a thorough Computational Fluid Dynamics (CFD) study with commercial FLUENT package will be performed. Specifically, we will compare the steady state and transient performance of the microburner for a wide range of operating parameters. Analysis of heat and mass transfer effects within the microburner will also be presented.

REFERENCES

[1] N.S. Kaisare, S.R. Deshmukh and D.G. Vlachos (2008), "Stability and Performance of Catalytic Microreactors: Simulations of Propane Catalytic Combustion on Pt," Chem. Eng. Sci., 63: 1098-1116. [2] N.S. Kaisare, G.D. Stefanidis and D.G. Vlachos (2009), "Comparison of Ignition Strategies for Catalytic Microdevices," Proc. Combust. Insti., 32: 3027-3034. [3] G.-B. Chen, Y.-C. Chao and C.-P. Chen, "Enhancement of hydrogen reaction in a micro-channel by catalyst segmentation," Int. J. Hydrogen Energy, 33 (2008) 2586?2595. [4] C. Phillips, A.B. Richoub, A. Ambarib and A.G. Federov, "Catalyst surface at a fractal of cost: A quest for optimal catalyst loading," Chem. Eng. Sci., 58 (2003) 2403?2408.