Vasudevan Raghavan

A fundamental study to investigate the emission characteristics of ethanol-blended fossil fuels is presented. Employing a heterogeneous experimental setup, emissions are measured from diffusion flames around spherical porous particles. Using an infusion pump, ethanol-fossil fuel blend is transpired into a porous sphere kept in an upward flowing air stream. A typical probe of portable digital exhaust gas analyzer is placed in and around the flame with the help of a multi-direction traversing mechanism to measure emissions such as un-burnt hydrocarbons, carbon monoxide and carbon dioxide. Since ethanol readily mixes with water, emission characteristics of ethanol-water blends are also studied. For comparison purpose, emissions from pure ethanol diffusion flames are also presented. A simplified theoretical analysis has been carried out to determine equilibrium surface temperature, composition of the fuel components in vapor-phase and heat of reaction of each blend. These theoretical predictions are used in explaining the emission characteristics of flames from ethanol blends. © 2010 Elsevier Inc.

A fundamental experimental study to determine the burning rates of ethanol and ethanol-blended fossil fuels is presented. Pure liquid ethanol or its blends with liquid fossil fuels such as gasoline or diesel, has been transpired to the surface a porous sphere using an infusion pump. Burning of the fuel takes place on the surface of the porous sphere, which is placed in an air stream blowing upwards with a uniform velocity at atmospheric pressure and temperature under normal gravity conditions. At low air velocities, when ignited, a flame envelopes the sphere. For each sphere size, air stream velocity and fuel type, the fuel feed rate will vary and the same is recorded as the burning rate for that configuration. The flame stand-off distances from the sphere surface are measured by post-processing the digital image of the flame photograph using suitable imaging software. The transition velocity at which the flame moves and establishes itself at the wake region of the sphere has been determined for different diameters and fuel types. Correlations of these parameters are also presented. © 2008 The Combustion Institute.

A preliminary study of the shape and the extinction characteristics of a diffusion flame established over a circular liquid fuel surface under the influence of an opposed air flow, is presented. Renewable liquid fuel such as ethanol is employed. A simple heterogeneous combustion setup, which consists of a cylindrical tube containing ethanol located at the bottom, is exposed to an opposed air flow from a coaxial circular pipe of same size located at the top at a fixed separation distance. Axial and radial extents of flame for different air flow rates are qualitatively analyzed. Burning rates of ethanol for different separation distances and air flow rates are recorded. For a fixed separation distance, at a particular air flow rate the flame extinction takes place. Extinction air flow rates and corresponding strain rates for different separation distances are presented. © 2008 Elsevier Inc. All rights reserved.

A numerical study of leading edge anchoring characteristics of diffusion flames established over a liquid ethanol film in a confined environment at atmospheric pressure under normal gravity with a forced air flow parallel to its surface is presented. A numerical model, which solves the transient, two-dimensional, gas-phase governing conservation equations with proper interface coupling conditions, is employed. The model uses a global single-step reaction for ethanol-air oxidation to model the finite rate chemical kinetics and an optically thin radiation model to account for thermal radiation losses by absorbing species in a nonluminous flame. Validation of the numerical model is carried out against the available experimental data in terms of temperature profiles. The effect of free stream air velocity on the fuel mass burning rate and the movement of the flame anchoring point is further investigated. The emphasis is on investigating flame anchoring point, located upstream of the leading edge at low air velocities, and its movement towards and away from the leading edge of the fuel surface, as the air velocity is increased. This is studied by defining and evaluating local or cell based chemical and flow time scales and their ratios. Copyright © Taylor & Francis Group, LLC.

In this study, based on the extinction characteristics of nonpremixed flames, global single-step kinetics parameters are estimated for ethanol oxidation in air. Using a quasi-steady heterogeneous experimental setup, the air velocity at which an envelope flame surrounding the sphere transits to a wake flame that burns in the rear region of the sphere, termed as the transition or the extinction velocity, were obtained in a previous study. These extinction velocities for different sphere sizes are employed to estimate the single-step kinetics parameters. The estimated global single-step kinetics has been employed in a numerical model and extinction characteristics of opposed-flow ethanol-air diffusion flames have been predicted and validated against the available experimental results in literature.