Search

Multiple single-channel meso-scale combustors assembling into a multi-channel meso-scale planar combustor is a good solution for elevating the output power of the micro-thermophotovoltaic system. Consequently, how to assembly a multi-channel meso-scale planar combustor for achieving higher output power comes to be an interesting issue. In this work, four representative four-channel meso-scale planar combustors, namely, combustor A, combustor B, combustor C and combustor D are designed. Extensive numerical investigations are conducted to compare the wall temperature of the four combustors under various hydrogen mass flow rates, hydrogen/air equivalence ratios and solid materials. Two variables, namely, mean wall temperature and nonuniformity coefficient of wall temperature are defined for comparing the wall temperature of the four meso-scale combustors. It is found that the purely counterflow four-channel meso-scale planar combustor D has more uniform and higher wall temperature compared with other combustors. Furthermore, the detailed heat transfer mechanisms of four different four-channel meso-scale planar combustors are analyzed and presented. In addition, some critical values are proposed for keeping high and uniform wall temperature on the purely counterflow four-channel meso-scale planar combustor. This work offers us great reference value for the design of multi-channel meso-scale planar combustor. [ABSTRACT FROM AUTHOR]

In this work, an improved counterflow double-channel micro combustor is designed. Computational Fluid Dynamics software Fluent is used to conduct numerical investigations on the thermal performance comparison between the old and improved counterflow double-channel micro combustors. It is found that the improved counterflow double-channel micro combustor has much higher and more uniform wall temperature compared that of the old one under various hydrogen mass flow rates, hydrogen/air equivalence ratios and solid materials. To make a quantitative comparison, the main results are presented as follows: (a) The improved combustor achieves the largest thermal enhancement at the hydrogen mass flow rate of 5.25 × 10 −7  kg/s when the hydrogen mass flow rate is ranged from 5.25 × 10 −7  kg/s to 9.8245 × 10 −7  kg/s. Namely, the mean temperature of upper and right wall is improved by about 9.66 K and 13.53 K, respectively, and the mean nonuniformity of upper and right wall temperature is reduced by about 23.24% and 26.79%, respectively. (b) The improved combustor achieves the largest thermal enhancement at the hydrogen/air equivalence ratio of 0.6, when the hydrogen/air equivalence ratio is ranged from 0.9 to 0.5. Namely, the mean temperature of upper and right wall is improved by about 27.55 K and 29.55 K, respectively, and the mean nonuniformity of upper and right wall temperature is reduced by about 23.24% and 19.51%, respectively. (c) The improved combustor achieves the largest thermal enhancement at the solid material of silicon carbide when the solid material is changed from quartz to silicon carbide. Namely, the mean temperature of upper and right wall is improved by about 16.77 K and 18.38 K, respectively, and the mean nonuniformity of upper and right wall temperature is reduced by about 26.47% and 28.41%, respectively. Finally, some guidelines are proposed for applications of the improved counterflow double-channel micro combustor in the micro-thermophotovoltaic system. [ABSTRACT FROM AUTHOR]

In order to extend the output power of the micro-thermophotovoltaic system, it is necessary to assemble multiple single-channel micro combustors into a multiple-channel micro combustor. As a result, how to assemble multiple single-channel micro combustors into a multiple-channel micro combustor comes to be an interesting issue. In this work, the counterflow combustion concept is used in a double-layer four-channel micro combustor, and three representative double-layer four-channel micro combustors are designed. Extensive numerical investigations are conducted to compare the thermal performance of the three different double-layer four-channel micro combustors under various hydrogen mass flow rates, hydrogen/air equivalence ratios and solid materials. Moreover, the purely counterflow double-layer four-channel micro combustor is compared with the counterflow single-layer double-channel micro combustor in our previous work under various H 2 mass flow rates, hydrogen/air equivalence ratios and solid materials. It is found that the purely counterflow double-layer four-channel micro combustor can keep more uniform wall temperature. And the purely counterflow double-layer four-channel micro combustor has better thermal performance compared with that of the counterflow single-layer double-channel micro combustor. Moreover, some critical values are given for keeping the merit of the purely counterflow double-layer four-channel micro combustor. [ABSTRACT FROM AUTHOR]

[Display omitted] • The constructed regression model is verified by ANOVA. • RSM and NSGA-II is combined for multi-objective optimization of PEMFC. • Effects of interaction term on power density,system efficiency and exergy efficiency are revealed. • The distribution of Pareto-optimal solutions is obtained. • The optimal design parameters of PEMFC are determined. This study optimized the performance of a proton exchange membrane fuel cell by combining the response surface methodology and non-dominated ranking genetic algorithm. Firstly, the design variables are determined, including operating pressure (p), operating temperature (T), Anode stoichiometry ratio (λ a), thickness of the proton exchange membrane (H mem) and gas diffusion layer (GDL) porosity (ε GDL). The objective functions are also identified, including power density (P), system efficiency (η) and exergy efficiency. Then, the Box-Behnken design is employed to arrange the numerical investigations. Analysis of variance is used to verify the appropriateness and reliability of the constructed regression models. Response surface analysis is used to show the interaction between each pair of design parameters. Finally, the Pareto optimal frontier is obtained by non-dominated ranking genetic algorithm II and the regression models constructed by response surface methodology. The Pareto optimal solution offers a power density of 0.6327 W·cm−2, a system efficiency of 26.16% and an exergy efficiency of 43.94 %, which is 13.18 %, 7.06 % and 20.29 % better than the initial direct current channel, respectively. The corresponding design variables is p = 2.6498 atm, T = 341.621 K, λ a = 1.1808, H mem = 0.0577 mm and ε GDL = 0.4908. This work provides a new multi-objective optimization method for designing more efficient proton exchange membrane fuel cells. [ABSTRACT FROM AUTHOR]

In this experimental investigation, four different types of biodiesel fuels were employed to investigate the effects of fatty acid methyl esters (FAMEs) proportion on emission and combustion characteristics of a marine diesel engine in terms of heat release rate, cylinder pressure, indicated power, brake specific fuel consumption (BSFC), CO emission, HC emission and NO x emissions. In accordance with international IS08178 standards, the experiments were carried out on a four cylinders direct injection diesel engine fueled with four different types of biodiesel fuels and pure diesel at two test cycle modes of E3 and D2. The experimental results showed that the kinematic viscosity and ignition delay time (IDT) of biodiesel fuel in combustion process played very important roles. The chemical IDT can be shorten by the higher saturation level and the kinematic viscosity will be increased due to the higher saturation contents like C18:0 and C16:0 together with C18:1 which is a single double bond methyl ester. The increased kinematic viscosity can result in poor evaporation process and poor fuel–air mixing. Lower kinematic viscosity methyl esters like C18:3 and C18:2 are beneficial for better combustion and fuel–air mixing, but the higher nitrogen oxide emission is discovered. Thus, the relationship between emission and combustion characteristics and proportion of biodiesel is not straightforward and simple, the balance of five majority components of biodiesel fuel is very significant. Compared with pure diesel, the oxygen content of biodiesel fuel improves the in-cylinder combustion. It is beneficial to decreasing HC and CO emissions and increasing NO x emissions. However, it is not obvious at low load. [ABSTRACT FROM AUTHOR]

An investigation on non-premixed H 2 /air combustion in a cylindrical micro combustor has been carried out. The effects of porous media and outer wall thickness on the combustion characteristics, flame location, thermal performance and energy conversion efficiency of the thermo photovoltaic (TPV) system were investigated. For the application of micro TPV system, a high and uniform outer wall temperature distribution is indispensable for the sustaining output, and the high energy efficiency is desirable. The results indicate that the setting of porous media or the increase of outer wall thickness can enhance the heat transfer in micro combustor and affects the flame stability, and the micro combustor with porous media and outer wall thickness b  = 0.2 mm obtains the lowest flame location. They are also conducive to the improvement of outer wall temperature and energy efficiency, the outer wall temperature of the micro combustor with a thicker outer wall and porous media is relatively uniform and the energy conversion efficiency of micro TPV system is also improved, the micro combustor with b  = 0.6 mm and porous media is more suitable for the application of micro TPV system. Additionally, the external thermal environment also can improve the outer wall temperature profile and the working performance of the micro combustor. [ABSTRACT FROM AUTHOR]

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 L 2 micro combustor, therefore, the L 2 micro combustor is more suitable for the micro thermo photovoltaic (MTPV) system when hydrogen volume flow rate is equal to 150 mL/min and equivalence ratio φ is equal to 1.0. [ABSTRACT FROM AUTHOR]