This article presents a computational study of wood volatiles combustion in a two-layer porous radiant burner (PRB) at different power inputs (1–3 kW) and porosity ranges from 0.7 to 0.9 ...respectively. A 2-D computational model is designed to numerically solve the combustion of wood-volatiles and air. A finite volume technique is utilized to solve governing equations including; continuity equation, momentum equation, species transport equation, radiative transport equation, and gas and solid phases energy equations. The utilized model is validated with previous literature for a two-layer porous radiant burner and the deviation of comparison is found within the acceptable range. The results reveal that the higher temperature was found in the central part of the burner and the minimum at the circumference. The longitudinal temperature distribution along the central line ruled out the occurrence of flashbacks. Moreover, the transport species contours reveal that the maximum combustion reactions occur in the upper layer of the porous zone. Further, the radiation efficiency decreases with input power and increases with porosity. The maximum value of radiation efficiency is found 36% at 1 kW and porosity of 0.9. while the minimum is 26% found at 3 kW and porosity of 0.7. The overall assessment showed that the PRB-based cooking stove is capable for providing a desired temperature range and efficient radiation efficiency in the range of 1–3 kW of power input.
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•Thermal and emission performances in a methane-ammonia fuelled micro-planar combustor are investigated.•There is a contradictory between CO and NO emission varied with the ...equivalence ratio Φ.•Higher N2O emission occurs at the rich condition, while it can be reduced by increasing inlet flow rate Vi.•Radiation efficiency is found to be increased with increased XNH3 at Φ ≤ 1 condition.•The outer wall mean temperature T-w is less sensitive to the blended ammonia concentration.
In the present study, thermal and emission performances of a micro-planar combustor fuelled with methane/ammonia mixture are numerically investigated. For this, a 3D low-Mach number solver is developed based on OpenFOAM. The effects of equivalence ratios Φ, inlet volume flow rates Vi, and ammonia molar fractions in the fuel XNH3 are considered. It is found that the outer wall mean temperature T-w and the non-uniformity R-Tw vary non-monotonically. There is a contradictory variation between CO and NO emissions with Φ. A higher N2O emission occurs under the fuel-rich conditions, while it can be reduced by increasing Vi. Vi plays a critical role in affecting thermal performance. Increasing Vi could lead to an increase of T-w. However, an appropriate Vi should be selected to avoid a higher R-Tw and a lower radiation efficiencyηr. The variation of NO and CO emission are insensitive to the variation of Vi. The variation of XNH3 almost has negligible effect on T-w but it can lead to a decrease of R-Tw, especially under fuel-rich conditions. Increasing XNH3 improves ηr at Φ = 0.8 and 1.0 while it has little effect at Φ = 1.2. The addition of ammonia can reduce the CO2 emission but lead to the increased NO emission. Increasing XNH3 results in the increase of CO emissions at stoichiometric conditions, but the decrease at rich conditions. N2O emission is observed to be increased first and then decreased with increased XNH3. This work provides a preliminary study on the thermal and emission performances of a methane-ammonia fuelled micro-thermo-photo-voltaic system.
Ammonia, as an alternative option of conventional hydrocarbon energy source, can achieve carbon free emission. However, the production of NOx is responsible for photochemical pollution and human ...health. In order to reduce NOx emission at the premise of guaranteeing energy conversion efficiency, three micro-combustors with different ring-shaped ribs in a cross-sectional view of 1) rectangular, 2) Ո-shaped and 3) Ս-shaped are proposed and fuelled by NH3. Extensive numerical comparisons are made with 3D models built by structured mesh. The effects of 1) inlet velocity, 2) equivalence ratio, 3) rib shape and 4) key parameters of these ribs are evaluated. In addition, the normalized sensitivity of NO formation and related reaction pathways are analyzed. It is found that the double-rib structure is more conducive to achieving better thermal performance. Besides, HNO is found to contribute the most of NO, while NH and NH2 are beneficial to the consumption of NO. When the dimensionless distance x between the rib and the combustor inlet is 3/9, comparing the condition of Φ being 1.1 and 1.0, NO emission is reduced by 47.0%, while the radiation efficiency is only decreased by 1.76%. This work has proven that a high energy conversion efficiency and a low NO emission can be achieved at the same time by properly optimizing the internal structure of the combustor in fuel-rich condition.
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•Micro-combustor with double ribs are studied in fuel-rich combustion.•NOx emission and thermal performance are evaluated in 7 cases.•Sensitivity of NO formation is analyzed under various equivalence ratios.•High radiation efficiency and low NOx emission can be achieved with proper design.
We provide results of antenna radiation and total radiation efficiency at millimeter-wave frequencies gathered with a new open-ended waveguide-plate method that is compared to a well-known ...two-antenna method. The new method yields improved uncertainty in antenna efficiency measurements. Both methods are based on use of a reverberation chamber. Measurement results are compared to numerical simulations and good agreement (~3% maximum difference) is achieved. Before performing the efficiency measurements, the chamber configuration was assessed with respect to the Rician K-factor, number of uncorrelated paddle orientations, and coherence bandwidth. We calculated the uncertainty using the NIST microwave uncertainty framework capable of performing parallel sensitivity and Monte Carlo analyses. The framework enables us to capture and propagate the uncertainties in the S-parameter measurements to the final efficiency result. The expanded uncertainty that we achieved for these antenna efficiency measurements is 2.60%.
As a renewable fuel, ammonia NH3 is identified as one of the most potential candidates to tackle greenhouse gas challenge. For this, ammonia-hydrogen-oxygen combustion in micro-power systems is ...numerically investigated in this work. The computational model is first validated with experimental data available in the literature. Then, emphasis is placed on the effects of (1) the fuel composition ratio ε (defined as the hydrogen molar fraction relative to the mixed fuel of ammonia and hydrogen) and (2) the wall thermal conductivity (WTC) on the system's working performance. Results indicate that increasing ε can not only lead to the outer wall temperature (OWT) and radiation efficiency (RE) being decreased, but also enable the flame propagate towards the combustor inlet. An optimized ε is found to minimize the NOx emission by approximately 54.9% compared to 100% NH3 combustion. Further analyses show that a high WTC has a potential to increase OWT at low fuel flow rates, while RE varies non-monotonically with the NH3 volumetric flow rate. It is also shown that WTC has a slight effect on NOx emission and the flame shape. This work sheds light on a simple but effective way to improve thermal and emission behaviors.
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•The fuel composition ratio ε plays a critical role in thermal and emission performance of NH3/H2-O2 micro-system.•Radiation efficiency is found to be decreased with increased ε.•Wall thermal conductivity has a dramatic impact on the outer-wall temperature.•Higher wall thermal conductivity leads to improved temperature uniformity.•NO formation and flame location are less sensitive to wall thermal conductivity.
In this communication, an <inline-formula> <tex-math notation="LaTeX">8 \times 8 </tex-math></inline-formula> dual-polarized traveling-wave antenna array is proposed and studied for in-band ...full-duplex applications. The proposed array consists of single-layer dual-polarized patch antennas with a simple feeding network. Despite the strong coupling among antenna elements, good suppression for the self-interference can be achieved by using differential feedings. To validate the study, an on-board prototype is developed, fabricated, and measured. The results show that good impedance matching responses are found, and high isolation of over 50 dB between the dual-polarized outputs is realized from less than 13.0 to 15.7 GHz. Meanwhile, small sidelobes and low cross-polarization levels with low insertion loss are observed, showing well-designed radiation responses.
This paper proposes a simple yet accurate method for estimating the antenna correlation coefficient (ACC) of a high‐order multiple‐input multiple‐output (MIMO) antenna. The conventional method ...employed to obtain the ACC from three‐dimensional radiation patterns is costly and difficult to measure. An alternate method is to use the S‐parameters, which can be easily measured using a network analyzer. However, this method assumes that the antennas are highly efficient, and it is therefore not suitable for lossy MIMO antenna arrays. To overcome this limitation, we define and utilize the non‐coupled radiation efficiency in the S‐parameter‐based ACC formula. The accuracy of the proposed method is verified by the simulation results of a 4‐port highly coupled lossy MIMO array. Further, the proposed method can be applied to N‐port arrays by expanding the calculation matrix.
In this paper two prediction models to evaluate the radiation efficiency of orthotropic plates, developed with different approaches, are presented. A sound radiation model, based on an ...analytical/modal approach, is developed for a thin orthotropic plate, with the principal directions aligned with the edges. The model allows to consider the contribution of each mode, either resonant or non-resonant, as well as the influence of fluid loading on the plate dynamic response and on sound radiation. Moreover, a statistical model to evaluate the average radiation efficiency, based on a non-modal approach, which only considers the contribution of resonant modes, is presented. These two models have been used in order to predict the radiation efficiency of orthotropic cross-laminated timber (CLT) plates. CLT is an engineered wood material constituted by an odd number of lumber beams glued together, which have become very popular in the last twenty years in the building construction market. Due to their layered structure, CLT plates might exhibit a highly orthotropic behaviour. Both prediction models are validated by comparing the simulated results with the experimental radiation efficiency, obtained by means of vibro-acoustic measurements on three CLT plates. Finally, the influence of fluid loading on sound power radiated by CLT plates is investigated.
In this communication, a novel leaky wave antenna (LWA) based on substrate integrated coaxial line (SICL) with a composite slot is proposed to achieve a beamforming pattern and high radiation ...efficiency. The composite slot is constructed by weighted superposing of a series of basic cosine-shaped slots. Then, beams generated by the weighted slots are superposed in the radiation pattern. By adjusting the slot parameters and the weighting coefficients, a cosecant-distributed radiation pattern is obtained. Due to the high radiation efficiency property of the basic cosine-shaped slots, the final radiation aperture length of the proposed antenna is only Formula Omitted, and the radiation efficiency is 67.5%. The open-stopband of the LWA at broadside radiation is naturally suppressed by the composite slot structure. Thus, the angle range of beamforming can cover broadside. The simulated and measured results demonstrate that the beamforming of the proposed antenna can cover a range from 0° to 40°.
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