Performance Of Micro-combustor Research Articles

Micro-combustor performance enhancement using a novel combined baffle-bluff configuration

This research is aimed at investigating a novel planar micro-combustor with combined baffle and bluff configuration for Micro-Thermo-Photo-Voltaic (MTPV) applications, numerically. It is shown that the novel combustor outperforms the similar configurations with only baffle or bluff, in terms of the flame stability, efficiencies, and emission. In addition, it is observed that the baffle thickness plays the key role in determining the flame location and, as the result, is the most important design variable controlling the temperature distribution and uniformity since the balance of heat transfer rates across the walls in different regions is significantly affected by this thickness. Moreover, small values of the bluff diameter and bluff-to-baffle distance result in performance improvements while the lower limit of these variables is set by the appearance of flame instability. In addition, for the optimal baffle thickness, the concurrent increase of 6.3% in the average wall temperature and 87.5% in the temperature uniformity are achieved. Finally, the sensitivity analyses reveal that the most effective parameter changing the combustion efficiency and entropy generation are the baffle length and wall conductivity, respectively.

Numerical investigation on the combustion characteristics of non-premixed hydrogen-air in a novel micro-combustor

A good mixing of fuel/oxygen is important for the non-premixed combustion in micro combustor, and the thermal performance of outer wall is of significant influence to the application of micro thermo photovoltaic (MTPV) systems. The non-premixed hydrogen/air combustion has been carried out in a novel micro combustor, in addition, the mixing performance of hydrogen/oxygen, the combustion characteristics, working performance of micro combustors are also investigated. Results show that the mixing performance of hydrogen/oxygen can be improved by the adoption of four pipes in combustor, and the thermal performance of combustor affects flame velocity, reaction rate and combustion efficiency. Moreover, the cavity or backward-facing step contributes to the heat recirculation and the flame stabilization, and a high and uniform outer wall temperature distribution is desirable for the application of MTPV system, which can be obtained at the hydrogen volume flow rate 90mL/min and the equivalence ratio 1.0.

Numerical investigation on hydrogen/air non-premixed combustion in a three-dimensional micro combustor

In order to obtain a higher combustion efficiency and a lager heat transfer from outer wall, a new type of micro cylindrical combustor with suction pipe, mixing pipe, diffuser pipe and shrinkage pipe and the combination of cavity and backward-facing step is designed and a numerical investigation on non-premixed hydrogen/air reacting flow inside three micro combustors has been carried out at atmospheric pressure. Moreover, the combustion characteristics and working performance of micro combustors are also investigated. Results show that the cavity and the backward-facing step in micro combustor is useful for the heat recirculation and the flame stability. Moreover, the combustion efficiency and the heat transfer from outer wall can be improved by increasing the length of combustion chamber within limited range. A high and uniform outer wall temperature distribution is desirable for the L2 micro combustor, therefore, the L2 micro combustor is more suitable for the micro thermo photovoltaic (MTPV) system when hydrogen volume flow rate is equal to 150mL/min and equivalence ratio φ is equal to 1.0.

Thermal performance of micro-combustors with baffles for thermophotovoltaic system

This paper presents a hydrogen-fueled micro-combustion system for thermophotovoltaic application. The thermal performances of the micro-combustor with and without baffles have been investigated numerically and experimentally. Dimensionless height λ and distance δ are defined to determine the optimal height and location of the baffles. The highest combustion efficiency is achieved when δ and λ are 0.3 and 0.9, respectively. The blowout limit is extended for the combustors with baffles. Besides, the heat from exhaust gas is recycled to preheat the fresh H2–air mixture, thereby increasing the mean wall temperature. A high H2–air mass flow rate will increase the fresh gas temperature but lead to low heat recovery rate.

Effects of wall thermal conductivity on entropy generation and exergy losses in a H 2-air premixed flame microcombustor

Microcombustion is a promising method for fulfilling the energy requirements of small-scale systems currently powered by portable batteries. However, its applications rely upon mitigation of heat losses, which adversely affect flame stability and performance. Heat losses in turn depend upon wall properties, especially thermal conductivity. It is thus necessary to systematically investigate the relationship between wall thermal conductivity and microcombustor performance using the exergy analysis. In this work, entropy generation rates of different irreversible processes in an annular microcombustor were computed for stoichiometric hydrogen–air mixture using CFD simulations of reactive flow for wall thermal conductivities in the range 0.1–325 W/m K. Chemical reaction, heat conduction, and mass diffusion were the dominant contributors to entropy generation, in the decreasing order. Irreversibilities due to combustion decreased as thermal conductivities increased. Diffusion contributions were most sensitive to the changes in thermal conductivity but chemical reaction and heat conduction contributions changed marginally. Results showed that walls did not contribute significantly to entropy generation, but increased wall heat losses at higher thermal conductivities adversely affected the exergetic performance of microcombustor through availability losses and by influencing the flow gradients. Based on the results of this study, wall thermal conductivity in the range 0.1–1.75 W/m K was found suitable in order to obtain uniform wall temperature profiles and high exergetic efficiencies.

The Investigation of Semi-Three-Dimensional Heat Transfer Modeling in Microcombustors

This paper presents a three-dimensional combustion model in the microcombustors. In this research, the flame structure is composed of three zones: a preheat zone, a reaction zone, and, finally, a post-flame zone. The governing equations are solved in these zones using the required boundary and matching conditions, which are achieved from nonasymptotic or asymptotic approach. Moreover, the role of Peclet number as a determining factor in the microcombustor performance is analyzed, and is found that by the increase of the Peclet number, the dimensionless flame temperature rises. Consequently, this three-dimensional model has provided a great description for the Peclet number, the dimensions, the asymptotic or nonasymptotic assumption effects, and the structural heat conduction in the microcombustors. The results are validated with those obtained from two-dimensional heat transfers modeling, and are in accordance with data published by former researchers.

Investigation over the recirculation influence on the combustion of micro organic dust particles

This paper investigates the role of recirculation and non-unity Lewis number on the combustion of organic dust particles. Since recirculation effect is more noticeable in micro-combustors, it is necessary to propose a modeling approach of this phenomenon to better simulate the performance of micro-combustors. In this research, in order to model the combustion of organic dust particles, it is assumed that the dust particles vaporize first to yield a known chemical structure which is oxidized in the gas phase, and the chemical structure of this gaseous fuel is assumed methane. To study the flame structure and solve the governing equations, it is considered that the flame structure consists of three zones titled the preheat-vaporization zone, the narrow reaction zone and finally the post flame zone. The recirculation phenomenon is evaluated by entering the exhausted heat from the post flame zone into the preheat zone. The solution is based on the following approach. First, the governing equations in each zone are nondimensionalized. Then the needed boundary and matching conditions are applied in each zone. After that, these equations and the required boundary and matching conditions are simultaneously solved with the analytical model. Consequently, the remarkable effects of recirculation and non-unity Lewis number on the combustion characteristics of the organic dust particles such as burning velocity and temperature profiles for different particle radii are obtained. The results show reasonable agreement with published experimental data.