Effects of hydrogen and steam addition on laminar burning velocity of methane–air premixed flame: Experimental and numerical analysis

Effects of hydrogen enrichment and steam addition on laminar burning velocity of methaneeair premixed flame were studied both experimentally and numerically. Measurements were carried out using the slot burner method at 1 bar for fresh gases temperatures of 27 °C and 57 °C and for variable equivalence ratios going from 0.8 to 1.2. The hydrogen content in the fuel was varied from 0% to 30% in volume and the steam content in the air was varied from 0 to 112 g/kg (0e100% of relative humidity). Numerical calculations were performed using the COSILAB code with the GRI-Mech 3.0 mechanism for one-dimensional premixed flames. The calculations were implemented first at room temperature and pressure and then extended to higher temperatures (up to 917 K) and pressures (up to 50 bar). Measurements of laminar burning velocities of methanee hydrogeneair and methaneeairesteam agree with the GRI-Mech calculations and previous measurements from literature obtained by different methods. Results show that enrich- ment by hydrogen increases of the laminar burning velocity and the adiabatic flame temperature. The addition of steam to a methaneeair mixture noticeably decreases the burning velocity and the adiabatic flame temperature. Modeling shows that isentropic compression of fresh gases leads to the increase of laminar burning velocity

Bias adjustment of satellite precipitation estimation using ground-based measurement: A case study evaluation over the southwestern United States

Reliable precipitation measurement is a crucial component in hydrologic studies. Although satellite-based observation is able to provide spatial and temporal distribution of precipitation, the measurements tend to show systematic bias. This paper introduces a grid-based precipitation merging procedure in which satellite estimates from the Precipitation Estimation from Remotely Sensed Information using Artificial Neural Networks-Cloud Classification System (PERSIANN-CCS) are adjusted based on the Climate Prediction Center (CPC) daily rain gauge analysis. To remove the bias, the hourly CCS estimates were spatially and temporally accumulated to the daily 1°×1° scale, the resolution of CPC rain gauge analysis. The daily CCS bias was then downscaled to the hourly temporal scale to correct hourly CCS estimates. The bias corrected CCS estimates are called the adjusted CCS (CCSA) product. With the adjustment from the gauge measurement, CCSA data have been generated to provide more reliable high temporal/spatial-resolution precipitation estimates. In the case study, the CCSA precipitation estimates from the proposed approach are compared against ground-based measurements in high-density gauge networks located in the southwestern United States. © 2009 American Meteorological Society

Effects of CO2-H2O dilution on the characteristics of CH4-air-O2 flames

International audience Study of non-premixed turbulent flames stabilized by a swirler Control of pollutant emissions / emissions standards Improve performances of combustion plants Investigations on flame characteristics Effects of oxygen enrichment Effects of steam and CO2 dilution Effects of swirl intensit

Numerical analysis of characteristics of biogas and syngas combustion

International audienceDevelopment of modular adapted energy concept- Gasifier - multi-fuel burner - boilerCharacterization of syngas and biogas flames - Experimentally: stability, pollutant emissions, temperature - Numerically: Calculations of laminar burning velocity, flame temperature, pollutants (NOx, CO)…This poster: some results of calculation

A New Combustion Method in a Burner with Three Separate Jets

Oxy-flames from burners with separated jets present attractive perspectives because the separation of reactants generates a better thermal efficiency and reduction of pollutant emissions. The principal idea is to confine the fuel jet by oxygen jets to favor the mixing in order to improve the flame stability. This chapter concerns the effect of equivalence ratio on characteristics of a non-premixed oxy-methane flame from a burner with separated jets. The burner of 25 kW power is composed with three aligned jets, one central methane jet surrounded by two oxygen jets. The numerical simulation is carried out using Reynolds Average Navier-Stokes (RANS) technique with k-ε as a turbulence closure model. The eddy dissipation model is applied to take into account the turbulence-reaction interactions. The study is performed with different global equivalence ratios (0.7, 0.8 and 1). The validation of the numerical tools is done by comparison with experimental data of the stoichiometric regime (Ф = 1). The two lean regimes of Ф = 0.7 and 0.8 are investigated only by calculations. The velocity fields with different equivalence ratio are presented. It yields to increase of longitudinal and transverse velocity, promotes the fluctuation in interaction zone between fuel and oxygen also a better mixing quality and a decrease of the size of the recirculation zone

Dark Energy and Modified Gravity

Despite two decades of tremendous experimental and theoretical progress, the riddle of the accelerated expansion of the Universe remains to be solved. On the experimental side, our understanding of the possibilities and limitations of the major dark energy probes has evolved; here we summarize the major probes and their crucial challenges. On the theoretical side, the taxonomy of explanations for the accelerated expansion rate is better understood, providing clear guidance to the relevant observables. We argue that: i) improving statistical precision and systematic control by taking more data, supporting research efforts to address crucial challenges for each probe, using complementary methods, and relying on cross-correlations is well motivated; ii) blinding of analyses is difficult but ever more important; iii) studies of dark energy and modified gravity are related; and iv) it is crucial that R&D for a vibrant dark energy program in the 2030s be started now by supporting studies and technical R&D that will allow embryonic proposals to mature. Understanding dark energy, arguably the biggest unsolved mystery in both fundamental particle physics and cosmology, will remain one of the focal points of cosmology in the forthcoming decade.Comment: 5 pages + references; science white paper submitted to the Astro2020 decadal surve

Effets de l'enrichissement en oxygène sur une flamme turbulente non-prémélangée, méthane-air, stabilisée par un swirl

Ce travail présente les effets de l’enrichissement en oxygène sur le comportement d’une flamme non-prémélangée méthane air dans un brûleur co-axial à swirl. L’étude porte plus particulièrement sur la stabilité de la flamme et les émissions polluantes telles que les NOx, CO2, CO et CH4. Les expériences sont menées dans une chambre de combustion cylindrique de 25 kW refroidie par une circulation d’eau. Le brûleur est constitué de deux tubes concentriques avec un swirl placé dans la partie annulaire afin de mettre en rotation l’oxydant. Le tube central achemine le méthane jusqu’à un injecteur radial qui comporte huit trous uniformément répartis situés juste en dessous du plan de sortie du brûleur. Les mesures des gaz brûlés sont effectuées par des analyseurs multi-gaz à l’aide d’une sonde de prélèvement en sortie de la chambre de combustion. Des expériences de chimiluminescence du radical OH* sont menées pour décrire la structure et la stabilité de la flamme dans les cas air et air enrichi en oxygène. Les hauteurs d’accrochage, les fluctuations de la base de la flamme, et les longueurs de flamme sont déterminées. Les mesures sont effectuées pour une concentration en oxygène qui varie de 0 à 40 % en volume, un nombre de swirl de 0,8 à 1,4 et une richesse globale de 0,7 à 1. Les résultats montrent que l’ajout de l’oxygène à l’air améliorent la stabilité de la flamme en étendant les limites de soufflage. L’augmentation de la concentration en oxygène conduit à une diminution des hauteurs de décrochage et une réduction des fluctuations de la base de la flamme. Les mesures ont montré que l’augmentation du nombre de swirl améliore significativement la stabilité de la flamme. L’analyse des gaz brûlés a révélé que les émissions de CO2 augmentent linéairement avec la concentration en oxygène. Les émissions de CO décroissent exponentiellement tandis que les émissions de NOx, augmentent exponentiellement avec l’enrichissement en oxygène