Ryan Seballos

Bio: Ryan Seballos is an academic researcher from Case Western Reserve University. The author has contributed to research in topics: Solid fuel & Flame spread. The author has an hindex of 1, co-authored 1 publications receiving 18 citations.

Concurrent flame spread over discrete thin fuels

Abstract: An unsteady two-dimensional numerical model was used to simulate concurrent flame spread over paper-like thin solid fuels of discrete configurations in microgravity (0 g with 20 cm/s) and in normal gravity (1 g). An array of ten 1 cm-long fuel segments was uniformly distributed in the flow direction (0 g) or in the vertical direction (1 g). A hot spot ignition source was applied at the upstream leading edge of the first fuel segment. The separation distance between the fuel segments was a parameter in this study, ranging from 0 (corresponding to a continuous fuel) to 3 cm. Using this setup, the burning characteristics, spread rate of the flame base, and the solid burning rate were examined. The flame base spread rates in both 1 g and 0 g cases increase with the separation distance. This is due to the flame jumping across the gaps. For the solid burning rate, the dependency on the separation distance is different in 1 g and 0 g cases. At a flow velocity of 20 cm/s in 0 g, the flame reaches a limiting length and the flame length is approximately the same for all fuel configurations. As the separation distance increases, the heating length (the fuel area exposed to the flame) decreases, resulting in a decreasing total heat input and a decreasing solid burning rate. In 1 g, the flame is long and extends to the last fuel segment before the first fuel segment burns out. This suggests that the heating length is approximately the same in all simulated cases (∼total fuel length). However, the flame standoff distance decreases when the separation distance increases. This results in an increasing total heat input and an increasing solid burning rate. Terrestrial experiments were conducted to validate the 1 g model. The experimental results agreed reasonably with the model predictions of burning characteristics, burn durations, and flame spread rates.

Understanding the effects of inclination angle and fuel bed width on concurrent flame spread over discrete fuel arrays

Abstract: Concurrent flame spread over discrete fuel arrays is a dangerous flame configuration where flame spread has the same direction with induced airflow. However, inclined upward flame spread over discrete fuels is rarely concerned, especially for the varied fuel bed width. In this study, birch rods were mounted in the regular array spaced 9 mm apart. 36 groups of arrays by varying six inclination angles (θ, 15°–90° with an interval of 15°) and six kinds of column numbers (n, 1–11 with an interval of 2) were designed to study the combined effect of inclination angle and array fuel bed width on flame spread over discrete fuel arrays. Average flame spread rate was found to be independent on the fuel bed width for n > 1 , and mass loss rate per total mass is restricted by air entrainment when θ ⩾ 75 ° or θ = 60 ° and n > 5 . As the inclination angle increases, the heat transfer mechanism changed from radiant dominance to convective dominance. Moreover, in the cases of radiant dominance, average flame spread rate was proportional to the squared incident heat flux. By simplifying burning zone, a prediction model of mass loss rate was developed. Based on the aspect ratio, burning zone was further divided into line ( λ ⩾ 3 ) and rectangular ( λ 3 ) fire sources, and then dimensionless correlations between the flame length and the heat release rate were proposed both for λ ⩾ 3 and λ 3 . In addition, during the upward flame spread process, flame length was found to be controlled by the competition between the accelerated upward buoyancy flow and the restriction of lateral air entrainment. This study provides a comprehensive insight for flame spread behavior of discrete fuels.

Experimental study of upward flame spread over discrete thin fuels

Abstract: Experiments are performed to study upward flame propagation over discrete combustibles separated by air gaps. An array of ten 1 cm-long 5 cm-wide filter papers is uniformly distributed on a vertical sample holder subjected to double-sided burn. The distance between the samples was varied from 0 to 4 cm. After being ignited from the bottom end, the flame spread process is recorded by front and side video cameras. A precision balance with 0.01g resolution is used to monitor the mass loss and deduce the solid burning rate. The results show that both flame spread rate and solid burning rate have a non-monotonic relationship with the gap size. The presence of gaps decreases the fuel load (fuel mass per unit length), which results in an increasing apparent flame spread rate as the gap size increases. The gaps also allow the lateral entrained air to push the flame closer to the sample surface, enhancing the conductive heat input to the samples. This results in an increased solid burning rate and flame spread rate. However, when the gap size is large, the effective heating length of the sample and hence the total burning rate decrease as the gap size increases. Eventually, the flame fails to spread.

Identifying the criterion for discrete flame spread over single-row birch rods

Abstract: Although discrete flame spread is a common phenomenon in the practical fire scenarios, such as a group of burning trees under bushfire, research gaps still exist to address the flame spreading criteria and the related spread characteristics. Therefore, through this study, a group of birch rods with different lengths (denoted by l within 60–100 mm) and spacings (S, 1–9 mm) were analyzed experimentally and theoretically. It was known that the critical criterion of discrete flame spreading is determined by the l and S, where a criterion of l≥3d (sample thickness) could predict the critical spacing between the separated birch rods. Theoretical models were also developed to predict the global flame spread rate and mass loss rate under various S and l. The predictions based on the newly developed models agree reasonably well with those experimental data. Global flame spread rate, mass loss rate and flame height increase first and then decrease along with a bigger S, where the dimensionless flame height shows a piecewise exponential relationship with the dimensionless heat release rate. The research outcomes of this study provide a theoretical basis for the fire risk evaluation of those discrete fire spread.

Concurrent-flow flame spread over thin discrete fuels in microgravity

Abstract: Microgravity experiments are performed to study concurrent-flow flame spread over an array of thin cellulose-based fuel samples, using NASA Glenn Research Center's 5.18 s drop tower. Sample segments are distributed uniformly, separated by air gaps, on a sample holder. The exposed width of each sample segment is 5 cm. Two segment lengths, 0.5 cm and 1 cm, are tested. The gap sizes are varied in different tests, ranging from 0.5 to 5 cm. In all tests, a low-speed air flow (30 cm/s) is imposed and the upstream-most fuel segment is ignited by an electrical ignition wire. Upon ignition, the flame spread is recorded by two video cameras from the front and side-view angles. Spread rates, flame lengths, and burning durations are extracted using a custom video processing code. Similar to continuous fuels, flame spread over discrete fuels is a continual process of ignition. A burning discrete fuel segment, before it is consumed, needs to ignite the subsequent segment in order to have flame propagation across the gap. During this process, larger gaps between samples reduce the effective fuel load, increasing the apparent flame spread rate. However, larger gaps also reduce the heat transfer between adjacent samples, decreasing the sample burning rate. As a result, as the gap size increases, the flame spread rate increases but the burning rate decreases. At the same gap size, the flame spread rate is higher for the shorter tested sample segments. When considering sample configurations of the same fuel ratio (fuel length over the summation of the fuel and gap lengths), the spread rates are similar. This trend remains until a critical gap size is reached and flame fails to propagate across the entire array of samples. The critical gap sizes are similar for the two tested sample segment lengths and are suspected to be determined by the flame length.

Upward Flame Spread Over an Array of Discrete Thermally-Thin PMMA Plates

Abstract: Experiments and theoretical analysis were conducted to investigate the upward flame spread over a homogenous PMMA plate and an array of discrete thermally thin PMMA elements. In the experiment, a digital video camera was used to record the flame spread process. An electronic balance and thermocouples were adopted to monitor the mass loss and pyrolysis front position, respectively, as a function of time. In the theoretical analysis, the mass loss rate of PMMA was correlated to the heat transfer during flame spread. The experimental results show that the flame spread rate peaks in the case of discrete PMMA elements with a fuel coverage around 80% rather than 100% (the homogenous case) because the gap with an appropriate spacing between neighboring elements accelerates the flame spread. However, the flame cannot spread over an array of discrete fuels at a coverage of 50% or smaller where the gap is too large to allow effective heat transfer required for flame spread. A smaller coverage of PMMA results in a larger mass loss rate per area since the gaps between elements can entrain more air to promote the burning. A logarithmic relation, that can well describe the mass loss rate as a function of PMMA coverage, was proposed based on the theoretical analysis and the fitting of experimental measurements.