Effects Of Combustor Geometry Research Articles

Effects of combustor geometry on the combustion process of an RBCC combustor in high-speed ejector mode

The combustion characteristics of high-speed ejector mode in a 2-dimensional strut-based RBCC (rocket-based combined cycle) combustor had been investigated numerically in a Mach 2.5 supersonic flow. The numerical approach had been validated by comparing numerical results with available experimental data. Besides, three different hydrogen-air chemical reaction mechanisms had also been compared. The effect of the combustor geometry on the combustion process was then discussed by analyzing the heat release distribution and flow field. It was found that the wall configuration, closeout angle of the converging location and converging ratio all have significant influences on the heat release distribution and flow field structures. It is demonstrated that a converging–diverging wall configuration is beneficial for the combustion process with significant heat release increase compared to the other wall configurations. In addition, the closeout angle of the converging location is also closely related to the combustion performance, and there exists an optimized closeout angle in a specific combustor geometry. It is also revealed that the major heat release region moves upstream obviously with increase in the converging ratio, leading to an enhanced combustion process. However, the converging ratio is still to be optimized to keep a balance between heat release increase and total pressure loss of the supersonic flow.

Evaluation criteria for a flameless combustor based on recirculation and mixing - A CFD approach

In the present work, the effect of combustor geometry and inlet air velocity on flameless critical parameters such as recirculation ratio and mixing is investigated. The main objective is to develop evaluation criteria for flameless combustors design based on these critical parameters. A simple lab scale combustor with central air jet arrangement is employed for the analysis. Three-dimensional computations were performed under non-reacting conditions using ANSYS Fluent. Reducing the air jet diameter to half its original value leads to a 100% increase in the recirculation ratio, which promotes flameless operation. Moreover, it results in a slightly more than 200% increase in turbulence intensity, which encourages hot products entrainment and accelerates mixing with incoming reactants. From another side, scaling down the combustor to half its original size results in 66% reduction of recirculation ratio, which might suppress flameless operation. Besides, it accelerates incoming reactants mixing in the near burner region due to the increased jet spreading and decay rate. These results show the considerable influence of combustor geometry on recirculation ratio and mixing. Furthermore, the critical role of later parameters in the previously reported transition between conventional and flameless combustion modes for the present combustor is demonstrated. A threshold value of recirculation ratio, Kcritical, is found critical for flameless operation and is noticed to increase with increasing excess air ratio. Therefore, the two parameters are linked together through a developed mathematical correlation. Finally, combustor geometry is represented through the dimensionless parameters; air jet to combustor diameter ratio, and combustor scaling factor. Recirculation ratio is linked to these parameters through additional correlations. Through these developed correlations, geometry aspects for flameless combustors can be preliminary identified and/or evaluated.

Effect of micro combustor geometry on combustion and emission behavior of premixed hydrogen/air flames

In this study, effect of micro combustor geometry on combustion and emission behavior of premixed hydrogen/air mixtures is numerically investigated. An experimentally tested micro combustor geometry is varied by establishing a cavity or a backward facing step or micro channels inside the combustor. Considering effect of combustor geometry on the amount of heat transferred through wall based on outer wall and combustor centerline temperature distributions, combustion behavior is analyzed. Emission behavior is examined by means of mixing conditions, combustion efficiency and maximum temperature value which are highly bound to geometric properties of a micro combustor. Turbulence model used in this study is Renormalization Group k-ε. For turbulence chemistry interaction, Eddy Dissipation Concept model is used. Multistep combustion reaction scheme includes 9 species and 19 steps. Numerical results obtained from this study are validated with published experimental data. Results of this study revealed that combustion in such combustors can be improved by means of quality of mixing process, residence time, combustor centerline and outer wall temperature distributions, conversion rate of input chemical energy to utilizable heat and emanated NOx levels from combustor outlet with proposed geometric variations.

Effect of combustor geometry on continuous spin detonation in syngas–air mixtures

Regimes of continuous detonation burning of syngas–air mixtures in transverse (spinning) detonation waves in a flow-type annular cylindrical combustor are considered. Mixtures of carbon oxide and hydrogen in proportions of 1/1, 1/2, and 1/3 are used. The varied parameters are the combustor geometry and the fuel injection system, as well as the flow rates of air and syngas. The influence of additional supply of air to the products on the detonation wave parameters, pressure in the combustor, and specific impulse is determined. The range of realization of continuous spin detonation of the syngas–air mixture in terms of specific flow rates of the mixture is expanded from 25 to 786 kg/(s ·m2). It is shown that additional supply of air increases the pressure in the combustor, the thrust, and the number of detonation waves, but decreases the detonation wave velocity. The flow structure in the domain of detonation waves is studied. For some values of the combustor expansion coefficient, a chart of detonation regimes in the coordinates of the fuel-to-air equivalence ratio and specific flow rate of air is constructed, and the specific impulse of the thrust force is calculated.

ВЛИЯНИЕ ГЕОМЕТРИИ КАМЕРЫ НА РЕАЛИЗАЦИЮ НЕПРЕРЫВНОЙ СПИНОВОЙ ДЕТОНАЦИИ СМЕСЕЙ СИНТЕЗ–ГАЗ — ВОЗДУХ

ВЛИЯНИЕ ГЕОМЕТРИИ КАМЕРЫ НА РЕАЛИЗАЦИЮ НЕПРЕРЫВНОЙ СПИНОВОЙ ДЕТОНАЦИИ СМЕСЕЙ СИНТЕЗ–ГАЗ — ВОЗДУХ

Effects of combustor geometry on hydrogen–air premixed flame combustion in an annular microcombustor

Heat losses at the walls and heat release are two competitive rate processes in microcombustion, and a microcombustor design must balance them appropriately for optimal performance. The primary objective of this work was to study the effects of some design variables on the processes influencing microcombustor characteristics and performance. A new compact and lightweight premixed hydrogen–air annular microcombustor was studied using a detailed computational fluid dynamics model validated against experimental data from literature. Heat reflux and flame stabilization were achieved by inserting a hollow tube in the combustion zone, which was also thermally isolated to reduce heat losses. It was found that the flame structure was insensitive to the thickness of inner tube, while wall temperature was not. On the other hand, a compact flame was obtained for larger aspect ratios, and wall temperature field did not alter significantly. Performance improved marginally with a higher thermal conductivity hollow tube. However, larger aspect ratio resulted in inferior thermal performance and non-isothermal walls. Thus, a configuration with smaller aspect ratio and thin-walled inner tube, possibly with a high thermal conductivity, was found to be desirable for good thermal performance. Finally, the model predictions indicated suitability of the design for intended applications.

Dynamic Behavior Simulations of Pulverized Biomass RDF Combustion

This study used a CFD solver, CFX, to simulate the pulverized biomass refused-derived fuel (RDF) dynamic combustion behavior inside a wall-fired furnace, and investigated the effects of combustor geometry, pulverized biomass RDF traces, and burner positions on its performance under various operating conditions. The results showed that the interactions between various burners can affect the pulverized biomass RDF dynamic behavior significantly. In particular, the probability of pulverized biomass RDF hitting the wall is controlled by the down-fired rate as well as inlet conditions. Finally, the NOx concentrations inside the furnace are predicted in the optimal operating condition (Case 3). The results can be used as a design reference for the optimal operational combustion condition of pulverized biomass RDF.