Micro-thermophotovoltaic System Research Articles

Experimental and numerical investigations on NH3/H2 fueled combustion in the combustor with block for improved micro power generation

To advance the application of zero-carbon fuels in micro-combustion, enhance energy conversion, and reduce NOx emissions in NH3/H2-fueled micro-power generators, a micro-combustor with an insertion block is proposed and tested under various chamber configurations and operational conditions. Experimental and numerical tests are conducted in micro-combustors with varied block settings, burner dimensions, NH3 blended ratios (mN), and fuel flow rates (Vf). The results indicate that mN significantly impacts the generation and consumption of H, O, and OH radicals, as well as NO, affecting flame regime and heat transfer. Specifically, adding 5∼15% NH3 improves the operating performance of the burner, with the highest mean temperature achieved in combustor #24C3-0.4 at mN=15%. Block insertion alters flame characteristics and enhances gas-wall heat transfer, the combustor with thinner blocks at higher mN and thicker blocks at lower mN contributes to better thermal performance. Furthermore, combustors with thinner blocks exhibit lower NO emissions. The working performance of the micro-thermophotovoltaic system can be enhanced by selecting the appropriate burner length with block thickness W=0.4 mm and position Lb=7 mm based on Vf. The maximum electrical power of 3.7 W is achieved with a burner length of 28 mm for the system using InGaAsSb cells at Vf=1200 mL/min.

Investigation on H2-fueled combustion characteristics and improvement of thermal performance in a micro-planar with arranged inlet-fins and bluff-bodies for micro-thermophotovoltaic

To improve the energy conversion and efficiency, a micro-planar with arranged inlet-fins and bluff-bodies is proposed for H2-fueled micro thermophotovoltaic system. Effects of inlet-fins and bluff-bodies setting and combustor dimensions on combustion properties, heat transfer and energy conversion are investigated and analyzed under various operating conditions. The results illustrate that the flame stability and heat transfer in combustion chamber with arranged inlet-fins and bluff-bodies are enhanced, where heat recirculation is formed and radiation temperature is boosted. According to the field synergy analysis, coupling effects of inlet-fins and bluff-bodies on burning and thermal process can be improved by the optimization of bluff-bodies setting, and the flow limit is also expanded. There is a balance of the burner dimensions effects on the augment of radiation surface area and the reduction of radiation temperature for micro power generation. Particularly, the micro-planar with La/L = 0.62 contributes to achieve a higher radiation density, and the highest electrical output Pe = 3.16 W is adopted in combustor C2-0.62 at mf = 6.751 × 10−5 kg/s. It is beneficial to promote energy output of micro-planar and the energy efficiency of micro-thermophotovoltaic system.

Optimizing micro power generation with blended fuels and porous media for H2-fueled combustion

To enhance the combustion stability and thermal performance of micro-thermophotovoltaic system, a combustor inserted porous media and varying channel heights for premixed H2/CH4/Air burning is proposed. The experimental and numerical methods are conducted to investigate the effects of CH4 addition, equivalence ratio, porous media, and chamber setting on combustion characteristics, heat transfer, and flame stability. The results indicate that a small fraction of CH4 addition and porous media insertion both enhance heat release and transfer of H2-fueled combustion, and the optimal CH4 blending ratio is influenced by chemical energy input. Appropriately increasing the equivalence ratio under high flow rates contributes to stabilize the flame and improve the combustor thermal performance. Furthermore, porous media effectively promotes flame stability and heat transfer efficiency, with longer porous media enhancing heat conduction and convection processes, thereby increasing the radiation temperature. Besides, increasing the channel height of the porous media combustor appropriately enhances the electrical power output of the power system. Besides, the maximum electrical output of 9.7 W is obtained in the porous media combustor with a channel height of 11 mm at mc = 20 %, Ф = 1.0 and mf = 9.448 × 10−5 kg/s, which is 7.2 W higher than the free flame combustor with h = 7 mm.

Experimental and numerical investigation on energy efficiency improvement of methane/propane added of hydrogen-fueled micro power generation

The micro-thermal power generation presents several challenges including reaction instability, large heat loss, and energy conversion. So, a micro-planar with multi-hole baffle for micro power generation is proposed with C3H8/CH4 blended and reaction sensitivity analyzed. Effects of fuel sensitivities, baffle settings, operating conditions on combustion characteristics and performance of thermal are analyzed. Experimental results revealed the thermal performance of H2-fueled combustion with blended CH4 and C3H8 can be improved, while the H2/CH4/air burning obtains a higher improvement by promoting flame anchoring and reducing heat losses. Thermal reflux and high temperature zones can be generated at appropriate baffle positions and hole sizes to enhance the operating micro-combustor performance. Optimized baffles and CH4 blending ratios significantly improved combustor output power and system efficiency. For instance, the maximum mean radiation temperature of 1347 K can be obtained in combustor C8-0.8 at mc = 25 % and mf = 4.08 × 10−5 kg/s. Meanwhile, micro-thermophotovoltaic (MTPV) system equipped with InGaAsSb cell can achieve a 3.4 W electrical power output and a system efficiency of 3.5 %. It provides solutions for recovering energy from exhaust gases and improving energy efficiency to develop efficient and sustainable micro-energy sources.

Numerical investigation of inserting conical ring into the micro-combustor with premixed hydrogen/air to enhance the heat transfer performance for the micro-thermophotovoltaic system

The low thermal performance of conventional micro-combustor (CMC) is one of the major obstacles hindering the development of micro-thermophotovoltaic (MTPV) system. In the present research, micro-combustor with conical ring (MCCR) is proposed to enhance the overall performance. A comparative study of the temperature field, pressure field, velocity field and combustion efficiency of the CMC and MCCR is conducted. The numerical results show that when the inlet velocity is 8 m/s, compared with the CMC, the mean outer wall temperature, combustion efficiency and pressure loss of the MCCR-6 increased by 32.3 K (2.6%), 0.05% and 718.6 Pa (273.4%), respectively, while the standard deviation of outer wall temperature decreased by 31.4 K (49.5%). Additionally, the MC made using SiC provides a better overall performance, the conical ring (CR) is installed at 6 mm from the step with better overall performance.

Energy and exergy analysis of a micro-thermophotovoltaic system equipped with porous foam heat recuperator

The exhaust gases from micro-thermophotovoltaic (TPV) systems have a high temperature, which can be used to preheat the incoming fuel/air mixture. Thus, in this study, a novel porous heat recuperator is proposed to improve the low efficiency of the TPV systems by recovering its wasted heat. Compared to the base case (TPV system with bare double-pipe recuperator) the TPV system equipped with alumina porous heat recuperator exhibits 153 % higher thermal effectiveness. Simulation results showed that using the porous foam recuperator, radiation and exergy efficiencies of the TPV system have increased by more than 44 % and 5 %, respectively. In particular, by applying 85 % porous alumina recuperator in the TPV system, the emitter wall temperature raised up to 1353 K leading to 74 % radiation efficiency with negligible pressure drop limited to 181 Pa. In addition, the utilization of multiple porosities for the foams inside the mixing chamber and annular return path is scrutinized to reach the best system performance. Results of the present study revealed that incorporating porous foam heat recuperators in TPV systems is a simple yet effective approach to design and fabricate practical high-performance TPV systems for portable power generation applications.

Numerical investigations on the performance enhancement of a hydrogen-fueled micro planar combustor with finned bluff body for thermophotovoltaic applications

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.

Numerical identifications of T-shaped rod effect on thermal performance and exergy efficiency in methane/air combustion

To maximize the power output of micro-thermophotovoltaic systems, achieving a high and uniform wall temperature is desirable. Towards this goal, this work proposes a novel combustor with inserting a T-shaped rod and assesses the effectiveness of such a strategy in determining the thermal and exergy performances with a validated computational model. Results indicate that introducing such strategy results in a 50.4 K wall temperature elevation and a 30.5 % decrease in the temperature standard deviation at the inlet velocity of 0.6 m/s. The effectiveness of applying a T-shaped rod on wall temperature is also found to be dependent on the inlet velocity. In addition, the optimal equivalence ratio associated with the highest wall temperature is shown to be stoichiometric caused by the relatively larger volumetric thermal power density. Further analysis of the pressure loss and exergy energy is performed. While the presence of a T-shaped rod can lead to an increase in the pressure loss, these are negligible relative to the ambient pressure. Furthermore, in addition to the temperature enhancement, the T-shaped rod combustor is associated with a higher exergy and exergy efficiency, which is beneficial to improving the energy efficiency of combustion devices. This work provides valuable insight into enhancing the wall temperature and energy conversion efficiency for micro-power systems.

Experimental and numerical investigation on H2-fueled micro-thermophotovoltaic with CH4 and C3H8 blending in a tube fully/partially inserted porous media

Energy conversion and utilization of micro-thermophotovoltaic (TPV) system are limited by the micro-combustor, so the stepped tube inserted with porous media (PM) is proposed for H2-powered systems with blending CH4 or C3H8. Effects of blended CH4 and C3H8 on the H2/air combustion are experimentally investigated and numerically simulated. The results show that the addition of CH4 and C3H8 improves the thermal performance at lower blending ratios to stabilize the combustion and increase the energy efficiency, and the addition of CH4 gives superior thermal performance compared to C3H8. In addition, to increase the power output of micro-TPV system, the effects of micro-burners with different PM setups are investigated under varied operating conditions, which indicate that the insertion of PM alters the flame regime, enhancing combustion stability and energy conversion. For instance, the maximum radiant efficiency is obtained in the burner with PM L3 = 19 mm at vp = 4 m/s, while burner with PM L3 = 25 mm gains the maximum radiant efficiency of 46 % at vp = 6 m/s and is 12.4 % higher than that without PM. Therefore, the power output of the burner with longer PM is higher at high flow rates. When vp = 8 m/s, the maximum radiated power and system output power of the micro-TPV system with InGaAsSb cells reached 81.2 W and 4.2 W, respectively.

Effect analysis on combustion performance enhancement of the hydrogen-fueled micro-cylindrical combustors with twisted tapes for micro-thermophotovoltaic applications

The main part of a micro-thermophotovoltaic (MTPV) system is the micro combustor (MC). In this work, the performance of the traditional micro combustor (TMC) and the micro combustor with twisted tape (MCTT) is investigated numerically under various inlet velocities (9 m/s-12 m/s), H2/air equivalence ratios (0.7–1.0), lengths of the twisted tape (4 mm–16mm), and pitches (4 mm, 5.33 mm and 8 mm). The results show that compared with the TMC, the MCTT with a 16 mm long twisted tape has a 114.7 K, 12.2 W and 15.0% increase in the mean outer wall temperature T¯w, radiation power Pemitter and emitter efficiency ηmc, respectively, at vin = 9 m/s. The outer wall temperature Tow is more uniform when the length of the twisted tape is 4 mm or 8 mm, the maximum drop in temperature standard deviation is 38.9 K when vin = 9 m/s. When the equivalence ratio φha is less than 0.9, the ηmc is not significantly improved with the increase of the length of the twisted tape. Overall, the MCTT offers better promise for applications in MTPV systems than the TMC.

Experimental investigation of blended H2/CH4 combustion in combustors with block for micro-thermophotovoltaic

To extend the operation conditions and improve the working performance of micro-thermophotovoltaic system, the combustor with varied block setting and length is proposed, where blended CH4/H2 is employed. Effects of CH4 addition, burner dimensions and parameters on combustion characteristics, energy conversion and multi-factors on working performance are investigated under various flow rates. Results demonstrate that the consumption and production of OH and H radicals are strongly impacted by the CH4 blending ratio, affecting the flame regime, burning heat release and heat transfer in the combustion chamber. And 5–15 % CH4 addition is beneficial to the improvement of burner thermal performance, where the highest radiation temperature is achieved at mCH4 = 15 % in combustor C24-0.4 under lower fuel flow rate, while it is also affected by the burner setting. A higher CH4 mixing ratio contributes to the combustor with thin block and the thicker block with lower CH4 addition can both contribute to achieve a better working performance. Besides, the augment of burner length extends the operating conditions and the radiant area, while it reduces Tw, and combustor C29-0.6 obtains the highest radiation power of 48.1 W and electrical power output of 2.9 W with a system efficiency 2.2 % at mCH4 = 10 %, Vf = 635 mL/min and Φ = 1.0. So, the appropriate CH4 addition, block setting and burner size can yield enhanced system performance.

Heat transfer enhancement and pressure loss analysis of hydrogen-fueled microcombustor with slinky projection shape channel for micro-thermophotovoltaic system

Micro thermophotovoltaic (MTPV) system, as a type of micro-combustion power system, possesses several advantages, including higher energy density, sustained and stable energy output, and significantly extended service life. The energy conversion performance of the MTPV system is known to be closely correlated with the thermal performance of the microcombustor. This study proposes a unique microcombustor for the MTPV system with a slinky projection form channel. The influence of the amplitude of the slinky projection, the slinky projection fins number, and the basic oscillating channel radius on the external wall temperature, temperature uniformity, and pressure loss are investigated by adopting the detailed hydrogen/air reaction mechanism with 3-D numerical models. The results show that the increase of the slinky projection amplitude and the slinky projection fins number can improve the external wall temperature. Compared to the traditional microcombustor, the average external wall temperatures of the microcombustor with a slinky projection amplitude of 0.4 mm are 31.6 K lower at an input velocity of 5 m/s. Additionally, when the input mixture velocity is 5 m/s, the average outer wall temperature improves by 29.4 K as the number of slinky projection fins grows from 10 to 42, and the pressure drop increases by 1.4 times. Furthermore, the basic oscillating channel radius is suggested to be 1.5 mm. In summary, this research provides a valuable method for enhancing the energy production of the MTPV system.

Numerical Investigation of Pin Fin Types on the Thermal Improvement of H2/Air Micro Burner

The micro-thermophotovoltaic system is a prospective power generation system. The radiation performance of exterior walls is a critical component of MTPV, as it effectively determines the overall energy output. At a mixture intake speed of 10 m/s, the MCPFs-Diamond exhibits the most favourable thermal performance, as evidenced by the thermal distribution and the highest average temperature of the exterior walls, which measures 1255.3 K. Its available radiation energy can reach up to 43.6 W. In the case of micro combustors that incorporate alternative shapes of pin fins, the highest values for both the average external wall temperature and the available radiational energy are achieved when the gas intake speed is set to 8 m/s.

Numerical investigation of H2/Air fueled micro combustion characteristics with trapezoidal ribs for micro thermophotovoltaic applications: Effect of rib height

In this numerical study, the impact of equidistant trapezoidal ribs on the characteristics of premixed H2-air micro-combustion was investigated, with a specific focus on the rib height. The study comprehensively examined flame structure, flame front position, flame speed, and combustion efficiency. A comparative analysis was performed between a backward-facing step micro combustor (MCSD) and micro combustors with varying rib heights: MCRD1 (0.5 mm), MCRD2 (0.6 mm), and MCRD3 (0.7 mm). The incorporation of trapezoidal ribs resulted in the creation of elongated and evenly distributed recirculation zones, significantly enhancing mixing and promoting flame stability, particularly at higher rib heights. The recirculation zones played a critical role in influencing the chemical reaction rate and the species distribution, leading to higher flame speed and greater combustion intensity. The findings highlight the outcomes of incorporating ribs in terms of combustion efficiency. The combustion efficiency values for MCRD1, MCRD2, and MCRD3 were recorded as 96.95%, 96.75%, and 96.61%, respectively, while the MCSD had a combustion efficiency of 97.14%. Hence, the recommended range of rib height is considered advantageous in ensuring an optimal balance between improved flame stabilization and maintaining a satisfactory level of combustion efficiency. The findings provide valuable insights for optimizing micro-thermophotovoltaic systems.

Optimisation of a micro-thermophotovoltaic with porous media inserted burner for electrical power improvement

To improve energy efficiency and electrical power output of H2-fueled micro-thermophotovoltaic, burning in combustors with varied porous media (PM) settings is experimentally and numerically studied. Effects of burner dimensions, PM settings and operating conditions on flow field, species distribution, combustion characteristics and heat transmission are investigated and analyzed. Results demonstrate that inserted PM strongly affects burning properties and combustor thermal performance, which is enhanced in larger size combustors. The combination of partially inserted PM with inlet-step is conducive to flame anchoring, improving the efficiency at higher flow rate in small combustor because of the high surface values of Nusselt number and heat flux. The fully inserted PM is beneficial to the heat transfer in chamber at lower flow rate and achieves the highest radiation power of large scale burner. The limit of flow rate is dramatically broadened with the augment of burner scale, such as mr = 2.65 × 10−5 kg/s to mr = 4.64 × 10−5kg/s, and the highest electrical power of micro-thermophotovoltaic system with burner 9D and InGaAsSb cells reaches to 2.81 W.

Employing Taguchi method to optimize the performance of a microscale combined heat and power system with Stirling engine and thermophotovoltaic array

This study proposes a biosyngas-fueled power system, which is a fusion between a micro-thermophotovoltaic (micro-TPV) system and a Stirling engine. The combustor in the micro-TPV is a coaxial tube made of platinum. Biosyngas was simulated using different compositions of H2 and CO mixture. The H2/CO/air mixture was delivered to the inner channel of the micro-TPV combustor, while the CH4/air mixture was delivered to the outer channel. This study realized a micro-CHP system with a combustion-driven TPV cell array, and a Stirling engine-driven power generation system. This micro-CHP system harvests energy generated through thermal radiation from the reactor's surface as well as thermal energy from hot flue gas. The results indicate that the overall efficiency of the biosyngas-fueled micro-CHP system was strongly dependent on fuel composition, fuel/air ratio, and flowrate mixture. Thus, Taguchi method was employed to find optimal operative conditions; the highest efficiency was achieved under a biosyngas composition of 80% CO and 20% H2, with a flow velocity of 6 ms−1, and an equivalence ratio of 1.2, and its corresponding overall efficiency reached 43%, incorporating 0.84 W electricity output by TPV cell array, 3.25 W electricity output by Striling engine-driven power generation system, and 325.5 W of water energy gained.

Improvement of thermal performance and energy efficiency of micro-thermophotovoltaic with the dual-inlet combustor at appropriate equivalence ratio

Micro-thermophotovoltaic is facing challenge caused by small size, large area-volume proportion and heat loss ratio, reducing the burning stability and output power. So, the dual-inlet combustors with exit-step and porous medium are proposed for micro-thermophotovoltaic system. Effects of equivalence ratio, exit-step and porous medium setting on combustion characteristic and thermal performance are conducted and analyzed. Results demonstrate that 1% air in the second-inlet is conducive to releasing heat of combustion and optimizing wall temperature distribution, where the total equivalence ratio of H2/air keeps 1.0. Furthermore, the exit-step with applicable length and channel height can generate heat recirculation and enhance working performance of micro-combustor, while the employment of porous medium can further enhance heat transmission of gas-wall and boost the radiation temperature Tw. Combustor CP13 with porosity ε = 0.85 obtains the highest average Tw of 1273.9 K at mf = 3.376 × 10-5 kg/s. With the increase of mf, system efficiency of the combustor with porous medium is increased, while that with exit-step reaches the maximum at mf = 4.501 × 10-5 kg/s. The highest output electrical power and efficiency are appeared in combustor CP15 with ε = 0.95 at mf = 5.626 × 10-5 kg/s, that is, 4.2 W and 2.2%.

Effects of different channels on performance enhancement of a nozzle hydrogen-fueled micro combustor for micro-thermophotovoltaic applications

Under the background of the international energy crisis, it is urgent to develop a micro-thermophotovoltaic system using hydrogen as combustion energy. In order to optimize the micro-combustor in the system, the nozzle micro-combustors with five different channels are designed. All nozzle micro-combustors are numerically studied by using the mechanism of 9 components and 19 elementary reactions within the ANSYS Fluent 20.0, and their advantages and disadvantages in thermal performance, flame performance and chemical reaction are compared. It is concluded that the nozzle micro-combustor with constriction-expansion channel has the best performance among the five micro-combustors because of its reasonable segmented structure. Then, a new type of nozzle micro-combustor with segmented channel is designed, and the numerical study of segmented micro-burners and non-segmented micro-combustors with different inlet velocities and hydrogen/air equivalence ratios shows that the thermal performance of segmented micro-combustors is much better than that of non-segmented micro-burners. Therefore, compared with non-segmented nozzle micro-combustors, segmented nozzle micro-combustors have better application potential in micro-thermophotovoltaic applications.

Exergy analysis and NOx emission of the H2-fueled micro burner with slinky projection shape channel for micro-thermophotovoltaic system

In order to improve the energy output of the MTPV system and reducing the NOx emission, a novel micro burner with a slinky projection shape channel for the MTPV system is proposed. To conduct the numerical simulation, 3-D models with detailed H2/air reaction mechanisms and the extended Zeldovich mechanism of NOx generation are employed. The influence of the slinky projection amplitude, slinky projection fins number, and the basic oscillating channel radius on the energy conversion characteristics and the NOx emission is investigated. The increase of the slinky projection amplitude and slinky projection fins number can improve the energy output and exergy efficiency, as well as reduce the NOx emission. When the slinky projection amplitude is 0.4 mm and the slinky projection fins number is 42, the exergy efficiency reaches the maximum value of 70.3%, while the energy output of MTPV reaches the maximum value of 4.99 W at 10 m/s. Meanwhile, the decrease of the basic oscillating channel radius can significantly decrease the NO mole fraction at the outlet. Generally, an efficient technique to increase energy output and reduce NOx emission for the MTPV system is to introduce a micro burner with a slinky projection shape channel.

Effects of structure parameters of tube outlet on the performance of a hydrogen-fueled micro planar combustor for thermophotovoltaic applications

In order to obtain high energy output power and energy conversion efficiency for micro-thermophotovoltaic system, in this work, a hydrogen-fueled micro planar combustor with tube outlet is designed. Effects of structure parameters of tube outlet (tube distance, tube cross section and tube number) on the performance of micro planar combustor are numerically investigated for thermophotovoltaic applications. Results suggest that the energy output and energy conversion efficiency of MTPV system is slightly increased with the increment of tube distance, and the pressure loss is slightly reduced. Moreover, compare with the micro planar combustor with the circular tube, the micro planar combustor with square tube is more suitable for MTPV system. Furthermore, with the tube number increasing from two to three, the energy output and energy conversion efficiency of MTPV system is increased by about 8.49%–9.38%, and the pressure loss is significantly reduced by about 44.54%–46.78%.