Curvature and velocity of methane-air Bunsen flame tips

PIV and photographic recording are used to measure the velocity of the fresh gas and the shape of the reaction layer in a region around the tip of a methane- air Bunsen flame attached to a cylindrical burner. The results compare well with numerical simulations carried out with an infinite activation energy reaction model. The experimental and numerical results confirm that the well-known linear relation between flame velocity and flame stretch derived from asymptotic theory for weakly curved and strained flames is valid for small and moderate values of the flame stretch if the modified definition of stretch introduced by Echekki and Mungal (Proc Combust Inst 23:455–461,1990) and Poinsot et al. (Combust Sci Technol 81:45–73,1992) is used. However, the relation between flame velocity and modified stretch ceases to be linear and approaches a square root law for large values of the stretch, when the curvature of the flame tip becomes large compared to the inverse of the thickness of a planar flam

Measurement of the burning velocity of strongly curved methane-air flames

An experimental and numerical study has been carried out of the region around the tip of a methane-air premixed flame attached to a circular laminar jet burner. On the experimental side, photographic records and PIV have been used to measure the shape of the reaction layer and the velocity of the gas around the tip of the flame. The numerical part of the study includes simulations of stationary axisymmetric flames with infinitely high activation energy reactions. The experimental and numerical results compare well with each other and allow to determine the curvature of the reaction layer at the tip and the velocity and strain rate of the fresh gas flow along the axis of the burner. These data, together with the planar flame velocity determined by extrapolating the velocity of the flame at the tip to the limit of zero stretch, are used to assess the well-known linear flame-velocity/flame-stretch relationship originally proposed by Markstein and later derived in the asymptotic limit of weakly curved and strained flames [1, 2], as well as the phenomenological modification proposed more recently by Mungal and coworker

Curvature and burning velocity of Bunsen Flame tips.

The burning velocity of a premixed flame propagating in a given flammable mixture is known to depend on the difference between the curvature of the flame and the so-called curvature of the flow, which is the strain rate of the flow of fresh gas along the normal to the flame divided by the burning velocity of the planar flame. The difference between the local burning velocity and the burning velocity of a planar flame in a gas at rest is proportional to the difference of the flame and flow curvatures. The proportionality factor is the product of the burning velocity of the planar flame and the Markstein length, which is an intrinsic property of the flame that characterizes its dynamics. The Markstein length can be determined experimentally by simultaneously measuring the curvature of the flame and the strain rate of the flow. To achieve this goal, we have set up a laminar jet burner and used two PIV systems to measure the gas flow velocity in two perpendicular planes normal to the flame. Each PIV system is composed by two Q-switched Nd: YAG pulse lasers (New Wave, maximum 120 mJ/pulse at 532 nm wavelength), a double-shuttered cross-correlation camera (PCO, 1392 × 1040 pixels) and a pulse generator (ILA GmbH) to synchronize all the components as well as the two PIV systems. Oil droplets are used for tracking the flow and the flame. They are formed by condensation after oil evaporation in a seeding chamber placed in the air line. Seeded air and fuel gas (CO,H2, CH4) are mixed in a settling chamber upstream of the burner and burned in a stationary Bunsen flame. The oil droplets evaporate in the flame preheating region, thereby allowing a dual tomography of the front

Local burning velocity in a Bunsen jet flame

A PIV-based system has been set-up for the simultaneous measurement of the local burning velocity of premixed flames and the flame stretch due to the flame front curvature and the incoming flow strain rate. For moderately short jet flames, these measurements allow an indirect determination of the Markstein length, according to Clavin and Joulin (C–J) theory. For tall flames, the flame curvature becomes relatively large in a region around the tip where the C–J theory breaks down. However, our experiments confirm the appearance of a new linear relation between burning velocity and curvature at the flame tip. This relation defines a new proportionality factor which is probably associated to the evolution from rounded tips to slender tips when the jet velocity is increased

Prevalence of reduced lung diffusing capacity and CT scan findings in smokers without airflow limitation: a population-based study

Exercise; Lung Physiology; Tobacco and the lungEjercicio; Fisiología Pulmonar; Tabaco y pulmónExercici; Fisiologia pulmonar; Tabac i pulmóBackground Population distribution of reduced diffusing capacity of the lungs for carbon monoxide (DLCO) in smokers and main consequences are not properly recognised. The objectives of this study were to describe the prevalence of reduced DLCO in a population-based sample of current and former smoker subjects without airflow limitation and to describe its morphological, functional and clinical implications. Methods A sample of 405 subjects aged 40 years or older with postbronchodilator forced expiratory volume in 1 s/forced vital capacity (FVC) >0.70 was obtained from a random population-based sample of 9092 subjects evaluated in the EPISCAN II study. Baseline evaluation included clinical questionnaires, exhaled carbon monoxide (CO) measurement, spirometry, DLCO determination, 6 min walk test, routine blood analysis and low-dose CT scan with evaluation of lung density and airway wall thickness. Results In never, former and current smokers, prevalence of reduced DLCO was 6.7%, 14.4% and 26.7%, respectively. Current and former smokers with reduced DLCO without airflow limitation were younger than the subjects with normal DLCO, and they had greater levels of dyspnoea and exhaled CO, greater pulmonary artery diameter and lower spirometric parameters, 6 min walk distance, daily physical activity and plasma albumin levels (all p<0.05), with no significant differences in other chronic respiratory symptoms or CT findings. FVC and exhaled CO were identified as independent risk factors for low DLCO. Conclusion Reduced DLCO is a frequent disorder among smokers without airflow limitation, associated with decreased exercise capacity and with CT findings suggesting that it may be a marker of smoking-induced early vascular damage.The EPISCAN II study has been a GlaxoSmithKline sponsored study (grant number: not applicable)

Unravelling young COPD and pre-COPD in the general population

COPD; General populationMPOC; Població generalEPOC; Población generalBackground Chronic obstructive pulmonary disease (COPD) is commonly diagnosed when the airflow limitation is well established and symptomatic. We aimed to identify individuals at risk of developing COPD according to the concept of pre-COPD and compare their clinical characteristics with 1) those who have developed the disease at a young age, and 2) the overall population with and without COPD. Methods The EPISCAN II study is a cross-sectional, population-based study that aims to investigate the prevalence of COPD in Spain in subjects ≥40 years of age. Pre-COPD was defined as the presence of emphysema >5% and/or bronchial thickening by computed chromatography (CT) scan and/or diffusing capacity of the lung for carbon monoxide (DLCO) 0.70. Young COPD was defined as FEV1/FVC <0.70 in a subject ≤50 years of age. Demographic and clinical characteristics were compared among pre-COPD, young COPD and the overall population with and without COPD. Results Among the 1077 individuals with FEV1/FVC 0.70, 350 underwent both DLCO testing and chest CT scanning. Of those, 78 (22.3%) subjects fulfilled the definition of pre-COPD. Subjects with pre-COPD were older, predominantly women, less frequently active or ex-smokers, with less frequent previous diagnosis of asthma but with higher symptomatic burden than those with young COPD. Conclusions 22.3% of the studied population was at risk of developing COPD, with similar symptomatic and structural changes to those with well-established disease without airflow obstruction. This COPD at-risk population is different from those that develop COPD at a young age.The EPISCAN II study was sponsored by GlaxoSmithKline

Author correction : A small Cretaceous crocodyliform in a dinosaur nesting ground and the origin of sebecids

Correction to: Scientific Reports https://doi.org/10.1038/s41598-020-71975-y, published online 17 September 202