Adria Carmona

Bio: Adria Carmona is an academic researcher. The author has contributed to research in topics: Combustion & Premixed flame. The author has an hindex of 1, co-authored 1 publications receiving 15 citations.

Experimental study of the channel effect on the flame spread over thin solid fuels

Abstract: We experimentally burn thin solid fuels and obtain the speed of the flame front when it propagates (1) within a narrow channel (closed cross section), (2) within a channel with lateral walls only and (3) through a free cross section (plain case). The latter configuration is the classical one and it has been extensively studied with analytical, numerical and experimental methods by other authors. Our experiments have been carried out at different geometrical configurations and angles of inclination of the sample and also at several values of oxygen molar fraction. All experiments are restricted to purely buoyant flow. Our main results are as follows: (1) sidewalls reduce the flame spread rate in a non-monotonous trend when varying its height; (2) in horizontal flame spread, two simultaneous flame fronts that propagate at different velocities may arise in the channel case at high oxygen levels. The fastest flame front speed may be higher than that obtained in the plain case; (3) in upward flame spread, the channel effect configuration produces the highest flame front speed. We finally analyze the correlation of the downward flame front speed data in terms of the Damkohler number.

Combustion and fire safety of energy conservation materials in building vertical channel: Effects of structure factor and coverage rate

Abstract: Experimental study on combustion and fire safety of energy conservation materials (extruded polystyrene, i.e., XPS) in vertical channel with front openings of building facade is conducted, and effects of channel structure factor (α) and curtain wall coverage rate (β) are revealed. The XPS flame in the vertical channel is turbulent. There is a correlation between the flame height and pyrolysis length: x f = m x p n , where m and n vary with the change in structure factor and coverage rate. Upward flame spread rate decreases first and then increases as β rises. When 0 ≤ β 0.2 , the restraining effect of vertical channel on air entrainment dominates, while for 0.2 ≤ β ≤ 0.8 , the heat feedback from curtain wall dominates. When β = 0, the influence of α on flame spread rate is not significant. The flame spread rate increases with increasing α when 0.2 ≤ β ≤ 0.8 . A model is established to predict the flame spread rate under different coverage rates and structure factors. Compared with experimental results, the prediction error is smaller than 10%. Larger values of flame height and flame spread rate correspond to higher fire hazard. This work is beneficial for fire safety assessment of building thermal insulation materials and optimal design of energy-saving curtain wall.

Opposed flow flame spread over thermally thick solid fuels: buoyant flow suppression, stretch rate theory, and the regressive burning regime

Abstract: The Michigan State University Narrow Channel Apparatus (MSU-NCA) was used to investigate opposed flow flame spread over samples of thermally thick Polymethylmethacrylate (PMMA). Three different fuel thicknesses were tested for mean airflow velocities 8-58 cm/s. The sample thicknesses were 6.6 mm, 12.1 mm and 24.5 mm, respectively. The measured flame position versus time determined the spread rate. Flame spread rates ranged between 0.02 - 0.07 mm/s depending on fuel thickness and mean opposed flow. Complete sample burnout occurred for the 6.6 mm and 12.1 mm samples at the critical flow velocity of 30 cm/s ± 5 cm/s and higher. The flame spread results appeared to be independent of flow velocities for this range (>30 cm/s): this plateau regime is identified as the regressive burning regime. The 24.5 mm thick samples never completely burned through, but they entered the regressive burning regime at 41.4 cm/s flow velocity. The nature of surface regression and its influence on the spread mechanism in this regime at high flow velocities was discussed for completely burned through samples (6.6 mm and 12.1 mm) and partially burned through samples (24.5 mm). For 12.1 mm thick samples, the flame spread results were compared with the same material (PMMA) and similar thickness (12.7 mm) results from the 1981 Fernandez-Pello et al. study. Their tests used a wind tunnel having a different length and cross-section than the MSU-NCA. The comparison was favorable when employing the stretch rate theory of flame spread incorporating the appropriate numerically computed stretch rate. Since buoyancy was an important factor in the 1981 study, when the buoyant stretch was also included, excellent agreement was obtained between the Fernandez-Pello et al. data and the current NCA data. The results demonstrated the effectiveness of the stretch rate theory for markedly different experimental configurations.

Spacing effects on downward flame spread over thin PMMA slabs

Abstract: To explore the flame spread mechanism over non-charring materials, the downward flame spread over polymethyl methacrylate (PMMA) samples is studied experimentally under the spacing scenarios of 2 mm, 7 mm, 13 mm, 19 mm and 25 mm. The experimental results show that: (1) As the spacing increases, the flame height, the length of the preheating zone and mass loss rate all increase first and then decrease. When the spacing is 13 mm, each value reaches the maximum. (2) As the spacing increases, the flame spread speed increases first and then decreases, approaching the single burning PMMA slab finally. In this study, a heat transfer model is proposed to examine the spacing effect over PMMA slabs. According to experimental results, a correlation between the flame spread rate and spacing is derived. Besides, experimental data agree well with the theoretical model.

Experimental study of concurrent-flow flame spread over thin solids in confined space in microgravity

Abstract: Concurrent flow flame spread experiments are conducted over thermally thin solid fuels in microgravity aboard the International Space Station (ISS) under varying levels of confinement. Samples of cotton fiberglass blended textile fabric are burned in air flows in a small flow duct. Baffles are placed parallel to the sample sheet, one on each side symmetrically. The distance between the baffles is varied to change the confinement of the burning event. Three different materials of baffles are used to alter the radiative boundary conditions of the space that the flame resides: transparent polycarbonate, black anodized aluminum, and polished aluminum. In all tests, samples are ignited at the upstream leading edge and allowed to burn to completion. The results show that at low flow speeds (

Influence of gap height and flow field on global stoichiometry and heat losses during opposed flow flame spread over thin fuels in simulated microgravity

Abstract: This study characterizes thin fuel opposed flow flame spread in simulated microgravity for a range of gap heights and airflow velocities in a Narrow Channel Apparatus (NCA). One objective was to estimate gap heights that suppress buoyancy without promoting excessive heat losses to the channel walls. A corollary of this objective was to assess the dependence of heat losses on the channel height. A second objective was to determine the influence of global combustion stoichiometry on simulated microgravity flame spread in the NCA. Whatman 44 filter paper was used for NCA gap heights ranging from 6–20 mm (half-gap below and above sample) and average opposed flow velocities 1–40 cm/s. Flames at low flows were fuel rich when the forced flows were of the same magnitude as the diffusive flow. For thin fuels, a full gap of 10 mm (5 mm half-gap) provided a compromise between buoyancy suppression and heat loss. Calculations were made of flame stoichiometry and of the influence of the velocity profile on flame spread rates (comparing it with previous theory). This part of the analysis provided support for the velocity gradient theory of flame spread. The information provided in this work on the theoretical nature of opposed flow flame spread over thin fuels is based on experimental measurements in simulated microgravity conditions.