Chenthil Kumar

Bio: Chenthil Kumar is an academic researcher from Indian Institute of Technology Madras. The author has contributed to research in topics: Flame spread & Premixed flame. The author has an hindex of 5, co-authored 6 publications receiving 79 citations.

On the role of radiation and dimensionality in predicting flow opposed flame spread over thin fuels

Abstract: In this work a flame-spread model is formulated in three dimensions to simulate opposed flow flame spread over thin solid fuels. The flame-spread model is coupled to a three-dimensional gas radiation model. The experiments [1] on downward spread and zero gravity quiescent spread over finite width thin fuel are simulated by flame-spread models in both two and three dimensions to assess the role of radiation and effect of dimensionality on the prediction of the flame-spread phenomena. It is observed that while radiation plays only a minor role in normal gravity downward spread, in zero gravity quiescent spread surface radiation loss holds the key to correct prediction of low oxygen flame spread rate and quenching limit. The present three-dimensional simulations show that even in zero gravity gas radiation affects flame spread rate only moderately (as much as 20% at 100% oxygen) as the heat feedback effect exceeds the radiation loss effect only moderately. However, the two-dimensional model with the gas radi...

A Computational Study on Opposed Flow Flame Spread Over Thin Solid Fuels with Side-Edge Burning

Abstract: A steady-state flame spread model has been used to study the effect of side-edge burning on flame spread over thin solid fuel strips of finite width. Simulations have been carried out for fuel strips with both inhibited (by metallic strips) and uninhibited side edges. The effect inhibition on both normal- and microgravity flame spread along with several intermediate gravity levels has been investigated. Such a study is important for understanding the physiochemical processes controlling the flame spread in low gravity where human experience is limited. Although simulations have shown an overall increase in spread rate for uninhibited cases for both normal- and microgravity flames, some effects such as flame spread variation with external imposed velocity and flame extinction limits show different behavior for microgravity and normal gravity flames. The heat and mass transport processes in the flame have been discussed in detail to explain the observed trends.

Opposed flow flame spread over an array of thin solid fuel sheets in a microgravity environment

Abstract: In this work a numerical study has been carried out to gain physical insight into the phenomena of opposed flow flame spread over an array of thin solid fuel sheets in a microgravity environment. The two-dimensional (2D) simulations show that the flame spread rates for the multiple-fuel configuration are higher than those for the flame spreading over a single fuel sheet. This is due to reduced radiation losses from the flame and increased heat feedback to the solid fuel. The flame spread rate exhibits a non-monotonic variation with decrease in the interspace distance between the fuel sheets. Higher radiation heat feedback primarily as gas/flame radiation was found to be responsible for the increase in the flame spread rate with the reduction of the interspace distance. It was noted that as the interspace distance between the fuel sheets was reduced below a certain value, no steady solution could be obtained. However, at very small interspace distances, steady state spread rates were obtained. Here, due to...

Gravity modulation study on opposed flame spread over thin solid fuels

Abstract: In this work a numerical investigation has been carried out to study the effect of g-jitter on zero-gravity (0 g e ) opposed flow spreading flame over thin solid fuels. For comparison simulations have also been carried out for normal gravity (1 g e ) downward spreading flames. G-jitter is emulated by gravity modulation of sinusoidal ( A ge sin(2 πt / T ge )) gravity perturbation ( g -perturbation) of a particular time-period ( T ge ) and amplitude ( A ge ) over a selected base gravity level (0 g e or 1 g e ). The response of flames at 0 g e base gravity and at 1 g e base gravity was different to the imposed g -perturbation. While at 0 g e the mean and the amplitude of the oscillatory flame spread rate (FSR) magnified with increase in the time period of g -perturbation, interestingly for the 1 g e flame a maximum mean FSR and oscillation amplitude occurs at certain perturbation time period. Further, at very small perturbation time-periods ( T ge ) the FSR at 1 g e was lower than the steady state FSR. The amplitude of oscillatory FSR increased with increase in perturbation amplitude ( A ge ). However, the 0 g e flame which is little affected (compared to 1 g e flame) at small perturbation amplitude ( A ge ) is affected severely at large perturbation amplitude ( A ge ). Both the gas phase and fuel pyrolysis (or fuel response) follow perturbation signal with a lag but fuel pyrolysis is more sluggish and lags behind gas phase. The phase lag between fuel pyrolysis and gas increases at smaller time-periods ( T ge ) and tends to enhance the effect of external perturbation whereas at larger time-periods ( T ge ) this lag inhibits the effect of external perturbation.

Opposed Flow Flame Spread Over Thin Solid Fuels: A 2D Numerical Study on Flame-Spread Transition from Normal Gravity to Zero Gravity and Vice Versa

Abstract: An unsteady two dimensional numerical model of flame spread is formulated to study the transient flame spread over thin solid fuels. The work focuses on the study of transient flame spread from a steady normal gravity flame to micro gravity flame and vice versa. The gas-phase is described by two-dimensional governing equations comprising of full Navier-Stokes equations for laminar flow along with the conservation equations of mass, energy and species. The specie equations are for fuel vapor, oxygen, carbon dioxide and water vapor. A one-step, second-order finite rate Arrhenius reaction between fuel vapor and oxygen is assumed. The thin solid fuel model comprises of equations of continuity and energy in the one-dimension parallel to the solid fuel surface along with a solid fuel pyrolysis law. The solid fuel considered here is an aerodynamically and thermally thin cellulosic material. The solid is assumed to burn ideally i.e. it vaporizes to form fuel vapors without melting. The radiation transport is mode...

I and i

Abstract: There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality. Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

Heat and Mass Transfer

Abstract: Thermophysical Properties Research Literature Retrieval Guide Edited by Y. S. Touloukian, J. K. Gerritsen and N. Y. Moore Second edition, revised and expanded. Book 1: Pp. xxi + 819. Book 2: Pp.621. Book 3: Pp. ix + 1315. (New York: Plenum Press, 1967.) n.p.

Solid combustion research in microgravity as a basis of fire safety in space

Abstract: This paper introduces fire safety standards for flammability evaluation of solid material intended for use in a spacecraft habitat. Two types of existing standards include material evaluation by pass/fail criteria corresponding to Test 1 of NASA STD 6001B and evaluation by a flammability index such as maximum oxygen concentration (MOC) corresponding to the improved Test 1. The advantage of the latter is the wide applicability of the MOC index to different atmospheres in spacecraft. Additionally, the limiting oxygen index (LOI) method is introduced as a potential alternative index for the evaluation using the improved Test 1 method. When criteria based on an index such as MOC or LOI are applied for material screening, the discrepancy of the index to the actual flammability limit in microgravity such as minimum limiting oxygen concentration (MLOC) is essential information for guaranteeing fire safety in space because material flammability can be higher in microgravity. In this paper, the existing research on the effects of significant parameters on material flammability in microgravity are introduced, and the difference between the limiting value in microgravity and the indices given by the standard test methods on the ground is discussed. Finally, on-going efforts to develop estimation methods of material flammability in microgravity according to normal gravity tests are summarized.

Effect of Diaphragms on Regression Rate in Hybrid Rocket Motors

Abstract: In this work, single-port, cylindrical grain laboratory-scale hybrid rocket motors are numerically simulated to study the effect of diaphragms. The effect of single and multiple diaphragms is investigated by varying diaphragm height, its axial location (for a single diaphragm), and spacing (for multiple diaphragms) at selected inlet GOX. A single diaphragm increases the local regression rate and its influence is prominent only in the region immediate downstream. Therefore, a tangible increment in average regression rate with a single diaphragm can only be realized for motors with small L/D( 10), use of multiple diaphragms are required to increase the regression rate and combustion effici...

Effect of swirl on the regression rate in hybrid rocket motors

Abstract: In this work, the effect of swirl on regression rate ( r b ) in a hybrid rocket motor is investigated numerically. The r b increased monotonically with inlet swirl number and was also found to depend on the inlet swirl profile. The swirl velocity profiles with the peak closer to the axis yielded higher r b . Parametric study on fuel grains of various lengths and diameters ( L / D ⩽ 25 ) shows that swirl is more effective in improving the average r b for short grains ( L / D 5 ) and large diameter grains.