Numerical Simulations of a Micro Combustion Chamber (original) (raw)
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International Journal of Engineering, 2014
A micro combustor is one of important devices in heat generation to power miniaturized products such as microrobots, notebook computers, micro-aerial vehicles and other small scale devices. An integrated micro combustor with thermophotovoltaic (TPV) in a micro-size electric generator supplies electricity to these micro devices. There is a growing interest in developing micro combustors as a power source due to their inherent advantages of higher energy density, higher heat and mass transfer coefficients and shorter recharge times compared to electrochemical batteries. A new micro combustion concept is described in this work by introducing a new terminology in the micro combustion. The effects of Area to Volume Ratio (AVR) of the micro-combustors were studied to find the best performance of designed micro-combustors. In order to test the feasibility of the designed micro combustors before the actual experiment is conducted, simulation work was performed. There are three key parameters involved in the current study: Area to Volume Ratio (AVR), Flow Velocity of the mixture (u), and Fuel-Air Equivalent Ratio (Ø). Main results of this experiment are images of temperature contour, graphs of temperature distribution profile, and graphs of mean temperature profile. This study found there is a specific range of mixture flow velocity (0.50-0.56 m/s) which result a high and uniform temperature distribution as well as its best mean temperature of micro combustion process. The simulation work could also localized the specific range of AVR-value (1.40-2.01) which require further investigation in the future.
LES Simulation of an Ultra-Micro Combustion Chamber Based on a 177 Reactions Mechanism
ASME 2010 10th Biennial Conference on Engineering Systems Design and Analysis, Volume 1, 2010
Goal of this paper is to investigate the performance of microcombustors, a field currently under rapid development in particular for propulsion, e.g., UAVs and micro-electrical power generators. This study focuses on a cylindrical microcombustor fed by methane and air, with diameter and height 0.025m and 0.06m respectively. A 3D LES simulation with the WALE subgrid scale models, the EDC combustion-chemistry model and the reduced GRIMech1.2 mechanism has been performed. The calculated maximum temperature inside the chamber, the gas exhaust temperature and the combustion efficiency are compared and discussed. Reported results are at 0.05s, that is after 5 residence times. This ultra-microcombustor displays an excellent combustion efficiency which makes it a suitable for application in ultrasmall energy producing devices. This work is part of a broader work that includes an experimental analysis, and it was conceived as a contribution towards a better understanding of the most convenient simulations guidelines for future microcombustor applications, and to a more accurate estimate of the performance parameters to apply to first-order design procedures.
Numerical characterization of a premixed flame based annular microcombustor
International Journal of Hydrogen Energy, 2010
Thermal inertia of the surrounding hardware or elaborate flow arrangement is used for external recirculation of heat in many microcombustors, increasing the weight and pressure losses. Recent research promotes hydrogen as a promising fuel for microcombustion due to its high heat of combustion. On this background, a hydrogen-fuelled microcombustor of simple construction was designed, which utilized the external thermal recirculation by a hollow nitrogen-filled tube inserted in the flame. The present paper reports stabilization and structure of a well stabilized stoichiometric H 2-air flame established in this microcombustor with the help of a detailed computational fluid dynamics model. Self-sustaining combustion could be achieved without any need for catalytic action. An asymmetric flame composed of two branches was stabilized on the walls at a location where the wall heat losses were balanced by the wall heat conduction. The flame thickness exceeded its characteristic one-dimensional value and flame zone broadened from the base to the tip due to heat losses and differential diffusion of hydrogen. Finally, the performance data for different inlet mass flow rates and wall thermal conductivities revealed useful operating points of the microcombustor for applications including micropropulsion, heating and portable electric power generation.
Numerical study on stabilization of flame inside micro-combustor
1ST INTERNATIONAL CONFERENCE ON MANUFACTURING, MATERIAL SCIENCE AND ENGINEERING (ICMMSE-2019), 2019
This work aims to numerically study the stabilization of flame in a MEMS based methane-air adiabatic microcombustor. Three different micro-combustor geometries were computationally simulated using premixed methane air-fuel in quartz micro-combustor with different configurations in order to determine the optimal micro-combustor design for the highest efficiency. The study was conducted to determine the design and characteristics of flame stabilization behavior in the micro-combustor. ANSYS Fluent application software was used to simulate the models. Premixed fuel of methane-air is used to stabilize the flame with a stoichiometric ratio of 0.6. The design of micro-combustor is modified by creating backward steps in the model, in order to create a recirculation zone to slow down the flow, which intends to stabilize the flame at center of the micro combustor. The model was analyzed for different inlet velocities, ranging from 0.5 to 2 m/s, of the premixed fuel. It is clear from the analysis that a micro-combustor with one backward step stabilizes the flame with highest efficiency for different inlet velocities.
Thermal performance characteristics of a microcombustor for heating and propulsion
Applied Thermal Engineering, 2011
Wall heat losses are a major impediment to ignition and flame stabilization in microcombustion. In this context, reactant preheating may improve flame stability in a microcombustor. This work is aimed at studying the flame response to changes in inlet temperature of an annular microcombustor burning hydrogeneair stoichiometric mixture. The proposed configuration uses a hollow inner tube filled with nitrogen to facilitate flame stabilization. A detailed axi-symmetric computational model for reactive flow was developed and tested for this purpose. The model predictions were used to evaluate suitability of the proposed design for gas turbine and other applications in terms of different indicators of thermal performance. The baseline data showed the operational feasibility of the proposed configuration. Reduction in the preheating zone length and improved ignition at the cross-stream sites combined to give an increasingly compact flame as inlet temperatures increased. However, the increased wall heat losses at higher inlet temperatures reduced the overall efficiency of microcombustor. This drawback offsets the gain obtained in the form of improved function of the inner tube due to higher inlet temperatures. As a result, the proposed configuration is suitable for gas turbine applications at low to medium values of the investigated temperature range subject to a critical assessment of increased heat losses and reduced heat reflux. The thermophotovoltaic and thermoelectric applications should be feasible at medium to high inlet temperatures.
Fuel, 2018
Main challenges for a fuel efficient micro scale combustion are rooted from size restriction of micro combustors which results with inappropriate residence time of fuel/air mixture and intensified heat losses due to relatively high surface to volume ratio of such devices. One way of increasing energy output of micro combustors is to optimize its geometry by considering simplicity and easy manufacturability. In this study, effect of combustor geometric properties on combustion behavior of premixed hydrogen/air mixtures was numerically investigated. For this purpose, an experimentally tested micro combustor's geometric properties were modified by establishing a backward facing step which is varying distance from combustor inlet and has varying step height, and adding opposing cavities which are varying distance from combustor inlet and have constant length to depth ratio into the flow area. Modeling and simulation studies were performed using ANSYS Design Modeler and Fluent programs, respectively. Combustion behavior was analyzed by means of centerline and outer wall temperature distributions, amount of heat transferred through combustor wall, conversion ratio of input chemical energy to utilizable heat, and species distributions. Turbulence model used in this study is Renormalization Group (RNG) k-ε. Multistep combustion reaction scheme with 9 species and 19 steps was simulated using Eddy Dissipation Concept model (EDC). Results showed that backward facing step in the flame region alters reaction zone distribution, flame length and shape, and consequently temperature value and distribution throughout the combustor. Lastly cavity was found to slightly increase peak temperature value.
Multi-Fidelity Combustor Design and Experimental Test for a Micro Gas Turbine System
Energies, 2022
A multi-fidelity micro combustor design approach is developed for a small-scale combined heat and power CHP system. The approach is characterised by the coupling of the developed preliminary design model using the combined method of 3D high-fidelity modelling and experimental testing. The integrated multi-physics schemes and their underlying interactions are initially provided. During the preliminary design phase, the rapid design exploration is achieved by the coupled reduced-order models, where the details of the combustion chamber layout, flow distributions, and burner geometry are defined as well as basic combustor performance. The high-fidelity modelling approach is then followed to provide insights into detailed flow and emission physics, which explores the effect of design parameters and optimises the design. The combustor is then fabricated and assembled in the MGT test bench. The experimental test is performed and indicates that the designed combustor is successfully implem...
International Journal of Hydrogen Energy, 2014
Lengthedepth ratio Flame-splitting limit Recirculation zone a b s t r a c t Combustion characteristics of H 2 /air mixture in a micro-combustor with wall cavities were investigated numerically. The effects of inlet velocity, equivalence ratio, and the length edepth ratio of the cavity were studied. The results show that at a high enough velocity the flame splits in the middle which leads to a large amount of fuel leakage and a sharp decrease in the conversion rate of hydrogen. Meanwhile, the flame splits at the inner wall which gives rise to two high temperature regions and double temperature peaks at outer wall. Moreover, the flame-splitting limit is extended at a higher equivalence ratio due to a more intensive reaction. Furthermore, the flame-splitting limit increases for a larger length edepth ratio of the cavity, whereas the wall temperature level decreases. Therefore, excessive large lengthedepth ratios are not beneficial for this type of micro-combustors if the combustor walls are used as heat sources of thermoelectric or thermal photovoltaic devices.
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.