Characteristics of air and oxy-fuel combustion in micro-channels (original) (raw)
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Microscale combustion: Technology development + fundamental research
2011
Technical paper by Yiguang Ju + Kaoru Maruta, 2011 Princeton University + Tohoku University Deals with combustion in demanding environments + under more difficult conditions, including rotary engine, quenching ... 47 pages > Content ... > Abstract 1 > Contents 1 > 1. Introduction 2 » 1.1 Needs of micro-scale combustion 2 » 1.2 Scaling parameters of micro-scale combustion 3 » 1.3 Development + challenges of micro-power generators 4 » 1.4 Challenges in fundamental research of micro-scale combustion 5 » 1.5 Focus of previous + the present reviews 5 > 2. Meso + micro-scale combustors 6 » 2.1 Micro-thrusters 6 » 2.2 Micro internal combustion engines 8 » 2.3 Micro reactors 10 > 3. Flame dynamics of micro-scale combustion 14 » 3.1 Premixed combustion 14 » 3.1.1 Flammability limit + quenching diameter 14 » 3.1.2 Heat recirculation 16 » 3.1.3 Flame + structure coupling 17 » 3.1.4 Thermal + kinetic quenching 20 » 3.1.5 Weak flame regimes with temperature gradient 23 » 3.2 Catalytic micro-combustion 25 » 3.2.1 Stability + flammability limits of catalytic combustion 25 » 3.2.2 Interaction / transition between gas-phase + surface reactions 27 » 3.2.3 Ignition of catalytic reaction 29 » 3.3 Non-equilibrium combustion 31 » 3.4 Flame instability 32 » 3.4.1 Repetitive extinction + reignition instability 33 » 3.4.2 Spinning instability 35 » 3.4.3 Spiral flames + pattern formations 37 » 3.5 Non-premixed combustion 38 » 3.5.1 Mixing liquid fuel vaporization 39 » 3.5.2 Formation of diffusion flame cells + flame streets in mesa + micro-scale combustion 41 > 4. Future research of micro-combustion 42 » 4.1 Low temperature meso-scale combustion for advanced engines 42 » 4.2 Microreactors for fuel reforming 43 » 4.3 Microreactors for boundary layer flow control 43 » 4.4 Micro-combustion launching new concept fundamentals 43 > References 43 german keywords: Wankelmotor / Kreiskolbenmotor English Keywords: Wankel Engine / Wankel Rotary Engine / Rotary Piston Engine / Rotary Combustion Engine The high energy density of hydrocarbon fuels creates a great opportunity to develop combustion based micro-power generation systems to meet increasing demands for portable power devices, micro unmanned aerial vehicles, micro-satellite thrusters, and micro chemical reactors and sensors. In this paper, the recent technological development of micro-power systems and progress in fundamental understanding of micro-scale combustion are reviewed. At first, micro-scale combustion regimes are categorized by using different physical and chemical length and time scales and the resulting nondimensional parameters and their correlations to various combustion regimes for micro and mesoscale combustion are discussed. Secondly, the recent successful developments and technical challenges of micro-thrusters, micro internal combustion engines, and micro chemical reactors summarized. Thirdly, the underlying fundamental mechanisms and ignition and flame dynamics in micro-scale combustion are reviewed, respectively, in premixed, non-premixed, catalytic, and non-equilibrium, micro-scale combustion systems. The conventional concepts of combustion limits such as the flammability limit, quenching diameter, and flame extinction and heat recirculation are revisited. The unique thermal and chemical transport mechanisms such as flame structure interaction, radical quenching, non-equilibrium transport appearing in micro-scale combustion are discussed. New flame regimes and instabilities such as flame bifurcation, weak flames, flame cells/streets, thermal and kinetic quenching, flameless low temperature catalytic combustion, repetitive extinction and ignition, spinning flames, spiral and multibranched flames, symmetric and asymmetric oscillating flames are discussed. Finally, an overview of future research and conclusion are made. The goal of this review is to present an overview of the development of micro-power generators by focusing more on the advance in fundamental understanding of micro-scale combustion.
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The optimal design of a microreactor for a specific application can be explored based on simulation results obtained by using CFD package of COMSOL Multiphysics. This research deals with the design of suitable microreactors for the catalytic oxidation of volatile organic compound (VOCs), using propane as a model molecule. The microreactor considered consists of eleven parallel channels, in which an Au/Cr/γ-Al2O3-catalyzed combustion reaction takes place. Each channel is 0.5 mm diameter and 100 mm long. The catalytic microreactor was simulated for temperatures between 563 K and 663 K and inlet flow velocities between 0.05 and 1 m/s. As expected, the propane conversion increased quickly with increasing temperature for a fixed inlet flow velocity. For a fixed temperature, the propane conversion increased as the inlet flow velocity decreased. The simulated results have revealed that higher conversion rates of propane can be achieved by decreasing inlet gas velocity from 1 m/s to 0.01 m/...
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The present paper aims to analytically investigate combustion phenomenon in microcombustors by using a two-dimensional model. The main objective is to analyze the effects of main parameters such as reaction zone thickness, maximum temperature and quenching distance throughout the combustor under catalytic and non-catalytic conditions. In solution of energy and mass equations, the temperature and mass dependant reaction rates are considered with an iterative procedure. The reaction zone thickness is considered as a variable and is predicted by the solution results of the present study. In order to validate the present model, the normalized magnitude of flame temperature is compared with published data, which shows an acceptable agreement and confirms the accuracy of the predicted data. The results show that the effect of catalytic surface on expanding flammability limits in a lean mixture is larger than the rich one.
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