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The aim of this study is to investigate the post-injection flow interactive effects of atomized fuel blends from an injector system of known characteristics into a direct injection compression ignition engine combustion chamber and their outcomes. Attempts were made to link the interactive influence of blend mixture quality,effluence and consumption rate of fuel injection properties on frictional loss, heat liberation, combustion, and volumetric efficiency performance outcomes of the engine. This numerical-experimental dimension study began with computational fluid dynamics (CFD) prediction of fuel in-cylinder behavior between a 225° CA (crank angle) (45°ABDC--after bottom dead center) and 360°CA (0° BTDC--before top dead center) compression stroke elapsing into an expansion stroke. A Testo gas analyzer was used to determine the combustion efficiency. The experiments validated the CFD outcomes presented. Willans lines were applied on blends to compare piston frictional losses. A swirl prediction maximum peak of 0.027237 at 336.15 CA for pure diesel blend (Di00) at 2,300 rpm and 0.066811 at 341.3 CA for pure biodiesel blend (B100) at 1,800 rpm aided the mixing quality. The instantaneous velocity on the sinusoidal profile and contour around the swirling peak crank angle revealed ignition activity resulting from high mixing quality. The engine possessed high-efficient fuel blends burning strength on a minimum of 54.5% at a higher flow rate. The engine speed and flow rate interaction on the heat liberation rate made a symmetric profile for D100 and B100. Engine energy loss on friction was minimal with D100 compared to B100 and 5% biodiesel to 95% diesel blend (B5). [ABSTRACT FROM AUTHOR]

In order to design a micro tube combustor with good thermal performance and flame stability for thermophotovoltaic applications, in this work, thermal performance and flame stability of hydrogen-fueled micro tube combustors with backward facing step and with injector are compared. It is found that the decrease of diameter ratio d 2 / d 1 leading to expansion of the symmetrical recirculation zone, which is helpful for fluid and heat circulation, and higher flame locations, which is not helpful for flame stabilization. Furthermore, effects of diameter ratio d 2 / d 1 on thermal performance and flame stability are analyzed and discussed. Results suggest that when the diameter ratio d 2 / d 1 is decreased from 0.9 to 0.8, positive effects of injector on thermal performance are enhanced and flame stability is improved under lower hydrogen/air equivalence ratio. Finally, the applications conditions of the micro tube combustor with injector are achieved. This work will provides us significant reference for designing micro tube combustor with injector. [Display omitted] • Thermal performance and flame stability of micro tube combustor with injector is investigated. • Effects of diameter ratio on the thermal performance and flame stability are revealed. • Conditions of thermal performance and flame stability enhancement are obtained. [ABSTRACT FROM AUTHOR]

To achieve higher power output and energy conversion efficiency for micro-thermophotovoltaic (MTPV) systems, a hydrogen-fueled micro planar combustor with finned bluff body is proposed and compared to the micro planar combustor with/without bluff body. Numerical results indicate that among micro planar combustors without bluff body, with bluff body, and with finned bluff body, the micro planar combustor with finned bluff body obtains a higher and more uniform wall temperature, but the pressure loss is higher. This is due to that the Peclet number near the inner walls is significantly higher compared to those without bluff body, and the Peclet number in the center of the axis is significantly lower, which reveals a stronger convection effect in the non-recirculation region and diffusion effect in the recirculation region. Then, effects of finned bluff body position, fin length/bluff body radius ratio and fin angle on the performance of micro planar combustor are investigated. It is found that the micro planar combustor with a larger finned bluff body position, smaller fin length/bluff body radius ratio and larger fin angle is more practical for MTPV system. [Display omitted] • A micro planar combustor with finned bluff body is designed. • Peclet number is introduced to clarify the performance enhancement mechanism. • Effects of structure parameters of finned bluff body are investigated. • Guidelines about designing micro planar combustor with finned bluff body are offered. [ABSTRACT FROM AUTHOR]

In order to further optimize the working performance of micro-cylindrical combustor, the combustion chamber of the micro-cylindrical combustor is inserted in a rectangular rib. Extensive numerical investigations are conducted to compare the exergy efficiency of non-ribbed and rectangular-ribbed micro combustors under various hydrogen mass flow rates and hydrogen/air equivalence ratios. Moreover, the effects of dimensionless rib positions and heights on the exergy efficiency of micro-cylindrical combustor are also widely investigated. Results suggest that the exergy efficiency of the rectangular-ribbed micro combustor is significantly higher than that of the non-ribbed micro combustor under different inlet conditions. Moreover, the exergy efficiency of the rectangular-ribbed micro combustor is significantly affected by the dimensionless positions l. The optimum dimensionless l is increased with the increase of hydrogen mass flow rate. This work offers us significant reference for optimizing the micro combustor in energy utilization. Image 1 • Exergy efficiency of rectangular-ribbed micro combustors is analyzed. • Exergy efficiency of micro combustor is greatly improved due to the inserted rectangular-rib. • Optimum rib position and height is achieved for higher exergy efficiency. [ABSTRACT FROM AUTHOR]

In order to reduce the entropy generation of premixed hydrogen/air flame in the micro combustion chamber, the combustion chamber of the old micro reactor is modified by gradually varying the diameter of the combustion chamber. Extensive numerical investigations about the entropy generation of premixed hydrogen/air flame in old and modified micro reactors are conducted under various hydrogen mass flow rates, hydrogen/air equivalence ratios, solid materials and inlet/outlet diameter ratios. Results suggest that the modified micro reactor has lower total entropy generation than that of the old micro reactor. This is attributed to that the temperature gradient of the burned gas in the modified micro reactor is lower than that in the old micro reactor after chemical reactions. Finally, the largest descent percentages of total entropy generation are achieved under various conditions, which provide significant reference values for hydrogen energy usage under micro scale combustion. Image 1 • A modified micro reactor is presented. • Specific entropy and total entropy generation are investigated. • The modified micro reactor has lower total entropy generation. • Largest decent percentages of total entropy generation are achieved. [ABSTRACT FROM AUTHOR]

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]

A high and uniform wall temperature on micro combustors is desirable for Micro-TPV system application. In this work, extensive numerical investigations of H 2 /air premixed combustion in the coflow and counterflow double-channel micro combustors are conducted under various H 2 mass flow rates, H 2 /air equivalence ratios and solid materials. Moreover, in order to characterize the uniformity of wall temperature, a nonuniformity coefficient R T ,w is introduced. Results show that the mean outer wall temperature of the coflow double-channel micro combustor is slightly higher than that of the counterflow double-channel micro combustor and the outer wall temperature nonuniformity of the counterflow double-channel micro combustor is greatly lower than that of the coflow double-channel micro combustor, meaning that the counterflow double-channel micro combustor has better thermal performance than the coflow double-channel micro combustor. More importantly, some critical values about the H 2 mass flow rate, H 2 /air equivalence ratio and solid material are determined for keeping the better thermal performance of the counterflow double-channel micro combustor. This design offers us another way for assembling the single-channel micro combustor into the double-channel micro combustor. [ABSTRACT FROM AUTHOR]

In order to obtain high energy output power and energy conversion efficiency for micro-thermophotovoltaic system, a hydrogen-fueled micro planar combustor with cavity is designed in this work. Numerical investigations on the performance of micro-cylindrical combustors with and without cavity are executed under different cavity length, outlet size and solid wall materials. Results show that the micro planar combustor with cavity can obtain a higher and more uniform outer wall temperature comparing with the micro planar combustor without cavity. With the reduction of cavity length and outlet size, the energy output and energy conversion efficiency of MTPV is much higher, while the pressure loss becomes larger. Thus, the optimal dimensionless cavity length and outlet size is 3/9 and 5/7 × 1/3, respectively. Furthermore, with the optimal cavity length and outlet size, nickel is used as the solid wall material for higher energy conversion efficiency of MTPV system, which increases to 3.86% at the inlet velocity of 5 m/s. As a result, the micro planar combustor with cavity is more suitable in MTPV system for higher energy output and energy conversion efficiency. [Display omitted] • A micro planar combustor with cavity is designed for thermophotovoltaic applications. • Effects of cavity on performance of a hydrogen-fueled micro planar combustor are investigated. • The optimal cavity length and outlet size is determined. • The total energy output and energy conversion efficiency of MTPV system is increased. [ABSTRACT FROM AUTHOR]

A high and uniform wall temperature on micro combustors is desirable for micro-thermophotovoltaic system application. In this work, an improved micro-cylindrical combustor with rectangular rib is developed. Numerical investigations on the combustors with and without rectangular rib are conducted under various H 2 mass flow rates and H 2 /air equivalence ratios. Moreover, the effects of dimensionless rib positions and heights on the outer wall temperature of micro combustors are also widely investigated. Results suggest that the improved combustor has a higher and more uniform outer wall temperature distribution under the same inlet condition compared with that of the micro combustor without rectangular rib. It is concluded that the inserted rectangular rib makes a recirculation region, enhancing the heat transfer between the combustor inner wall and burned gas. In addition, among all the investigated geometrical models, the geometrical model with the dimensionless rib position of 5/9 and dimensionless rib height of 0.4 has the highest and most uniform outer wall temperature where the H 2 mass flow rate and H 2 /air equivalence ratio are fixed at 5.25 × 10 −7 kg/s and 1.0, respectively. More importantly, the optimum dimensionless rib position is related with the inlet velocity of H 2 /air mixture and it is increased with the inlet velocity of H 2 /air mixture. [ABSTRACT FROM AUTHOR]

Energy conversion efficiency of a micro thermophotovoltaic (TPV) system strongly depends on wall temperature of micro combustors and its uniformity. In this work, a 3D numerical model is built to investigate effects of inlet pressure on premixed H 2 /air combustion in a micro-cylindrical combustor with a step. The variation of velocity, temperature and specific entropy field are analyzed. Moreover, in order to characterize the uniformity of wall temperature, a nonuniformity coefficient R T ,w is introduced. Results suggest that the variation of velocity, temperature and specific entropy field is mainly existed at the reaction and outlet regions. And the highest mean wall temperature (1265.59 K) is arrived at p in = 0 MPa, while the lowest nonuniformity coefficient R T ,w (5.06) and the highest exergy efficiency (40.29%) is approached at p in = 0.1 MPa. In the viewpoint of energy usage, the micro combustion system has the best performance at p in = 0.1 MPa due to that it has the potentiality to obtain better energy conversion efficiency and higher exergy efficiency. This work provides us a direction to improve the performance of the micro combustor without changing the structure of the micro combustor, and can combine with other optimization methods. [ABSTRACT FROM AUTHOR]

In order to enhance the thermal performance of micro-cylindrical combustors for micro-thermophotovoltaic applications, a micro-cylindrical combustor with cavity is designed. Extensive numerical investigations on micro-cylindrical combustors with and without cavity are implemented under different inlet velocities, hydrogen/air equivalence ratios and solid wall materials by ANSYS Fluent 16.0 with 9-species-19-reactions mechanism. It is found that the thermal performance of micro-cylindrical combustors with cavity is much better than that of micro-cylindrical combustors without cavity. This is attributed to that the cavity makes the burned gas closer to the back part of solid walls. Then, effects of cavity length and depth are analyzed and discussed. The optimal cavity length and outlet diameter of cavity is 6 mm and 2 mm, respectively. The mean outer wall temperature reaches 1306.88 K. Meanwhile, the mean nonuniformity of outer wall temperature is relatively low. All in all, the micro-cylindrical combustor with cavity has better potentiality for applications in micro-TPV system compared with the micro-cylindrical combustor without cavity. [Display omitted] • A micro-cylindrical combustor with cavity is developed. • Thermal performance enhancement mechanism of the designed micro combustor is revealed. • Thermal performance enhancement under different conditions is obtained. • The optimal cavity length and outlet diameter of cavity is determined. [ABSTRACT FROM AUTHOR]

In order to address the issue about the low output power of the micro-thermophotovoltaic system, in this work, the inlets of the traditional micro planar combustor are modified into injectors for better thermal performance and higher output power of the micro-thermophotovoltaic system. The thermal performance of traditional and modified micro planar combustors is numerically investigated and compared. It is found that the thermal performance of the modified micro planar combustor is greatly enhanced with the help of the injectors. This is due to that the reduction of the step diameter leads to the rise of the velocity of the inlet flow, resulting in the chemical reaction zone is closer to the center of the combustion chamber in the micro planar combustor. Furthermore, the positive effects and negative effects on thermal performance enhancement brought by the reduction of the step diameter of injectors are vividly discussed under different hydrogen mass flow rate, hydrogen/air equivalence ratio and solid wall material. Finally, some guidelines are proposed for the applications of the micro planar combustors with injectors in the micro-thermophotovoltaic system. This work provides us a simple and practical way to address the issue about the low output power of the micro-thermophotovoltaic system. • Micro planar combustors with injectors are designed and investigated. • Thermal performance enhancement mechanism of the designed combustor is clarified. • Reduction of step diameter has significant effects on thermal performance enhancement. • A largest improvement of 22.56 K on mean wall temperature is achieved. [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]