Thermoacoustic analysis of lean premixed hydrogen flames in narrow vertical channels

Thermoacoustic instabilities arise for lean hydrogen-air flames propagating in narrow channels. We provide here a detailed experimental analysis of such phenomena in a semi-confined vessel, analyzing the effect of the mixture composition, geometry and gravity on the onset of acoustic-driven flame vibrations. Downward-propagating flames leaner than a critical value vibrate smoothly and transit to the secondary oscillating instability, which develops strong variations of pressure that couple with the propagation dynamics. The transition threshold changes during the propagation along very narrow channels, where heat losses are no longer negligible. The parametric region of equivalence ratio for the secondary thermoacoustic instability diminishes, showing an additional transition for very lean flames. There, the front breaks into several structures and the flame-wave feedback becomes weaker. The influence of gravity is studied by comparing upward and downward propagating flames, where the Rayleigh–Taylor instability arises for sufficiently small values of the Froude number in slow-propagating lean flames. For a constant mixture, buoyancy-driven upward-propagating flames develop less wrinkled fronts than those propagating downwards, and remain unresponsive to acoustic-front interaction. We show here a direct relation between front shape and thermoacoustics. In agreement with previous studies [1], [2], [3], curvature and strain effects on conduction and diffusion characterize the response of the flame to pressure perturbations, with the Markstein number controlling the aforementioned transition. Nevertheless, the theoretical analyses found in the literature can only be used on nearly equidiffusional mixtures, and are not accurate enough to describe the highly diffusive fuel mixtures (i.e. lean hydrogen-air flames) considered in our experiments.This work was supported by projects ENE2015-65852-C2-1-R (MINECO/ FEDER, UE), BYNV-ua37crdy (Fundación Iberdrola España) and KIT. The authors want to thank the technical support of ProScience GmbH. in the construction and operation of the experimental setup. D. Martnez-Ruiz would like to acknowledge F. Higuera for fruitful discussions.Publicad

Influence of the application of Jasmonic Acid and Benzoic Acid on Watermelon fruit quality.

In watermelon crops in Southeastern Spain, important thermal differences appear during the first stages of plant development that can affect them. This work shows the effect of applying jasmonic acid and benzoic acid (JA+BA), inductors of systemic acquired resistance (SAR) and induced systemic resistance (ISR), respectively, on fruit quality parameters from a crop in a greenhouse in Southeastern Spain, where crops face a remarkable abiotic stress. We assessed two treatments of JA+BA, T1 (500+500 ppm), T2 (2000+2000 ppm) and a control test using an experimental design of randomized blocks with four replications. The results obtained for the parameters assessed (ºBrix, flesh firmness, rind thickness, polar and equatorial diameter) did not show statistically significant differences. The results showed that there was no metabolic cost in the plants when applying the assessed treatments of JA+BA

Effect of the application of jasmonic acid and benzoic acid on grafted watermelons yield under greenhouse conditions in the southeast of Spain for mitigation of stress

One of the main problems of watermelon crops in Sou theast Spain is the thermal difference because of c limatic conditions that appear during the first stages of the crop. The objective of this work was to evaluate the effect of inducing the systemic acq uired resistance (SAR) and the induced systemic resistance (ISR) through the application of jasmonic ac id (JA) and benzoic acid (BA), respectively, to counter the abiotic stress. We assessed two treatments of JA and BA, T1 (500 mg·kg-1 + 500 mg·kg -1 ) and T 2 (2000 mg·kg -1 + 2000 mg·kg -1), as well as a control test using an experimental design of randomized blocks with four replications. The results obtained for kg·m -2, fruits/m², kg/plant and fruits/plant did not show statistically significant differences. However, we obtained statistically sig nificant differences in the average fruit weight co mpared with the control test in the two experiments carried out in 2009 and 2010. The results showed that there was no metabolic cost in the plants when applying the assessed treatments of JA and BA

Fault-tolerant unfalsified control for PEM fuel cell systems

The article addresses the implementation of a data-driven control strategy in a real test bench based on proton exchange membrane fuel cells (PEMFCs). The proposed control scheme is based on Unfalsified Control (UC), which allows adapting in real-time the control law by evaluating the performance specifications based only on measured input-output data. This approach is especially suitable to deal with non-linearity, model uncertainty and also possible faults that may occur in PEMFCs. The control strategy has been applied to several experimental practical situations in order to evaluate not only the system performance but also different fault scenarios. The experimental results have shown the effectiveness of the proposed approach to regulate the oxygen stoichiometry in real-time operation as well as to maintain a proper system performance under fault situations. Also, a start-up mass-flow controller is added in order to bring the system towards its normal operating conditions.Peer ReviewedPostprint (author’s final draft

The role of conductive heat losses on the formation of isolated flame cells in Hele-Shaw chambers

The propagation of low-Lewis-number premixed flames is analyzed in a partially confined Hele-Shaw chamber formed by two parallel plates separated a distance h apart. An asymptotic-numerical study can be performed for small gaps compared to the flame thickness deltaT . In this narrow-channel limit, the prob- lem formulation simplifies to a quasi-2D description in which the velocity field is controlled by domi- nant viscous effects. After accounting for conductive heat losses through the plates in our formulation, we found that the reaction front breaks into one or several isolated flame cells where the temperature is large enough to sustain the reaction, both in absence and in presence of buoyancy effects. Under these near-limit conditions, the isolated flame cells either travel steadily or undergo a slow random walk over the chamber in which the reacting front splits successively to form a tree-like pathway, burning only a small fraction of the fuel before reaching the end of the chamber. The production of quasi-2D circular or comet-like flames under specific favorable conditions is demonstrated in this paper, with convection, conductive heat losses and differential diffusion playing an essential role in the formation of the isolated one and two-headed flame cells.This work was supported by the project ENE2015-65852-C2-1-R (FV,MSS,DMR) and ENE2015-65852-C2-2-R (DFG,VK) (MINECO/FEDER, UE). Daniel Martínez-Ruiz would like to thank Amable Liñán for fruitful discussions

Experimental analysis of oscillatory premixed flames in a Hele-Shaw cell propagating towards a closed end

An experimental study of methane, propane and dimethyl ether (DME) premixed flames propagating in a quasi-two-dimensional Hele-Shaw cell placed horizontally is presented in this paper. The flames are ignited at the open end of the combustion chamber and propagate towards the closed end. Our experiments revealed two distinct propagation regimes depending on the equivalence ratio of the mixture as a consequence of the coupling between the heat-release rate and the acoustic waves. The primary acoustic instability induces a small-amplitude, of around 8 mm, oscillatory motion across the chamber that is observed for lean propane, lean DME, and rich methane flames. Eventually, a secondary acoustic instability emerges for sufficiently rich (lean) propane and DME (methane) flames, inducing large-amplitude oscillations in the direction of propagation of the flame. The amplitude of these oscillations can be as large as 30 mm and drastically changes the outline of the flame. The front then forms pulsating finger-shaped structures that characterize the flame propagation under the secondary acoustic instability. The experimental setup allows the recording of the flame propagation from two different points of view. The top view is used to obtain accurate quantitative information about the flame propagation, while the lateral view offered a novel three dimensional perspective of the flame that gives relevant information on the transition between the two oscillatory regimes. The influence of the geometry of the Hele-Shaw cell and of the equivalence ratio on the transition between the two acoustic-instability regimes is analyzed. In particular, we find that the transition to the secondary instability occurs for values of the equivalence ratio phi above (below) a critical value phi(c) for propane and DME (methane) flames. In all the tested fuels, the transition to the secondary instability emerges for values of the Markstein number M below a critical value M-c. The critical MarkstPublicad

H2 purity control for highpressure alkaline electrolyzers

This paper proposes a control strategy that mitigates the cross contamination of H2 and O2 in a high-pressure alkaline electrolyzer, which consequently increases the supplied gases purity. In order to reduce the diffusion of gases through the membrane, the controller establishes the opening of two outlet valves based on the pressure of the system and the difference in liquid level between both separation chambers. Therefore, a multiple input - multiple output optimal controller is designed here. For this purpose, an available high-fidelity model was simplified in order to obtain a control-oriented model. The proposed controller was evaluated in simulation using the high-fidelity nonlinear model in a wide operating range and was compared with a pair of decoupled PI controllers. The resulting impurity of gases was below 1% in all cases.This work has been partially funded by the DEOCS project (DPI2016-76493-C3-3R).Peer ReviewedPostprint (author's final draft

Suppression of thermoacoustic instabilities by flame-structure interaction

We present here an experimental study of the influence of the aeroelastic coupling between the combustion chamber walls and the acoustic fluid field on the onset and development of thermoacoustic instabilitiesin stoichiometric propane-air premixed flames. A horizontal quasi-two-dimensional Hele-Shaw chamber formed by two parallel plates separated a small distance h is used. The flames are ignited at the open end, in contact with the atmosphere, and propagate towards the opposite closed end. The experiments reveal three distinct propagation regimes determined by the stiffness of the plates and the evolution of the pressure perturbation generated during ignition: (i) for sufficiently rigid plates, we observed secondary acoustic instabilities with large amplitude oscillations in the direction of propagation of the flame; for flexible enough walls to be compliant with ignition-related pressure changes, (ii) the propagation of the flame undergoes small-amplitude oscillations (primary acoustic instabilities) along the channel or (iii) it is smooth with no oscillations whatsoever. The flexural rigidity of the plate is modified experimentally by changing both the widthW and thickness hw of the top plate of the Hele-Shaw cell. The data recorded by the pressure transducer and the accelerometer is used to plot a stability map in the W - hw parametric space to define the combination of structural parameters that triggers the onset of thermoacoustic instabilities. Our experimental measurements, supplemented with results from a theoretical analysis of the walls vibration modes, indicated that deformation-induced volume changes of around 0.1% of the volume of the Hele-Shaw cell are sufficient to suppress thermoacoustic instabilities.This work was funded by the Agencia Estatal de Investigación of Spain under grants PID2019-108592RA-C43 and PID2019-108592RB-C41, and by the Regional Government of Madrid (Comunidad de Madrid-Spain) under the Multiannual Agreement with UC3M (H2SFE-CM-UC3M). The authors wish to thank the technical knowledge and assistance of David Díaz, Israel Pina and Manuel Santos in the design, construction and operation of the experimental setup. The assistance of Rubén Palomeque in the preparation of figure 6 is greatly acknowledged. We would also like to acknowledge Raúl San Miguel and Ramón Zaera for providing the values of E and v of the PMMA plates. Funding for APC: Universidad Carlos III de Madrid Read & Publish Agreement CRUE-CSIC 2022

Effects of exogenous enzymes and application method on nutrient intake, digestibility and growth performance of Pelibuey lambs

Pelibuey sheep is the main breed in the tropical and subtropical regions of Mexico, and high demand of sheep meat has favored the finishing of lambs in feedlots with diets containing high levels of grains. The objective of this study was to evaluate the effects of exogenous enzymes (EE) and application method on nutrient intake and digestibility and performance of growing Pelibuey lambs. Treatments were based on comparison of two different methods of adding an enzyme product (sprayed on the total mixed ration or applied orally to the lambs) versus control treatment (no added enzyme). Twenty-one Pelibuey lambs, weighing 15.7 kg (SD = 1.8 kg) initial body weight, were individually housed in shaded pens and assigned randomly to one of the three enzyme treatments. At the end of study (lasting for 45 days), three lambs from each treatment were randomly selected and adapted to a pants and harness designed for fecal collection to measure nutrient digestibilities. Total body gain and average daily gain were affected (P < 0.05) by supplemental EE. The application method of EE had significant (P < 0.05) effect on FCE and FCR, but no effects were observed on nutrient intake. Supplemental EE did improve (P < 0.05) the digestibilities of dry matter, organic matter, neutral and acid detergent fiber, but no differences were observed in crude protein digestibility. The application method of EE had significant (P < 0.05) effect on the digestibility of acid detergent fiber. Supplemental EE can improve body weight gain and nutrient digestibilities without affecting nutrient intake in Pelibuey lambs, but the results of feed conversion efficiency and acid detergent fiber digestibility depend on the application method used of the E

Sistema Informático para la Gestión Financiera de la Secretaría Ejecutiva Trinacional del Plan Trifinio (SIGEFI)

SIGEFI es un sistema que integra tres módulos, presupuestos, contabilidad y tesorería, por medio del cual llevan un control de sus movimientos financieros y transacciones diarias, además de generar ciertos informes para su control. Actualmente la Secretaría Trinacional del Plan Trifinio posee el sistema integrado de control de proyectos (SICOP) con el que administra presupuestos, contabilidad y tesorería, con dicho sistema está teniendo problemas de inconsistencias, información no validada e incompleta, además desde su implementación en el 2003, las necesidades de información han crecido. SIGEFI brinda una administración eficaz a la institució