Experiments employing porous sphere technique are carried out to investigate the combustion characteristics of biodiesel produced from karanja oil and its blends with diesel and gasoline. Biodiesel or its blend is transpired to porous sphere surfaces, where it burns. Porous spheres are placed in an air stream blowing with a uniform velocity at atmospheric pressure and temperature under normal gravity conditions. At low air velocities, a flame envelops the entire sphere. Fuel feed rates are recorded for various sphere sizes and air velocities. Overall, the visible flame shape is analyzed with the help of digital flame image. At a particular air velocity, the flame will not envelope the sphere, but establish near the rear region of the sphere and the same is recorded for different sphere sizes. Theoretical correlations are proposed for burning rate as a function of effective Reynolds number and for Damkohler number as a function of Froude number.

Vasudevan Raghavan

Department of Mechanical Engineering

Shintre Parag

Burning rate

Critical velocity

INFUSION PUMP

KARANJA OIL

POROUS SPHERE TECHNIQUE

Atmospheric pressure

Biodiesel

combustion

Flammability

Pumps

Reynolds number

velocity

Spheres

IIT Madras is a public technical and research university located in Chennai, Tamil Nadu. Founded in 1959, it is recognised as an Institute of National Importance.

IIT Madras has been ranked as the top engineering institute in India for four years in a row by the National Institutional Ranking Framework of the MHRD

It currently offers undergraduate, postgraduate and research degrees across 16 disciplines in Engineering, Sciences, Humanities and Management. About 596 faculty belonging to science and engineering departments and centres of the Institute are engaged in teaching, research and industrial consultancy.

IIT Madras

Investigation of Combustion Characteristics of Biodiesel and Its Blends

Combustion Science and Technology

Characteristics of methanol diffusion flames burning under three different configurations with respect to the directions of forced and natural convective flow fields are presented for zero and normal gravity conditions. Combustion of a spherical methanol particle and of a methanol film within a mixed convective environment, have been numerically simulated. The effects of gravity on aiding, opposing and perpendicular flow are presented. The gravitational field considerably changes the flow field, flame shapes and fuel burning rates, especially for the opposing flow case. © 2006 Elsevier Ltd. All rights reserved.

International Communications in Heat and Mass Transfer

Effect of gravity on methanol diffusion flames burning within a forced convective environment

In this work, experimental and numerical investigations of spheres burning in a convective environment have been carried out. In the numerical simulations, transient axi-symmetric Navier-Stokes equations along with species and energy conservation equations are solved using a finite volume technique based on non-orthogonal semi-collocated grids. A global single step reaction involving two reactants, two products and one inert species together with an Arrhenius rate equation has been used to model kinetics. For the sake of comparison, an infinite rate chemistry model has also been attempted. The density of the mixture has been evaluated from ideal gas equation of state. Thermo-physical properties like thermal conductivity and viscosity have been evaluated using the Chapman-Enskog description of binary gas mixtures. Specific heats and species enthalpies have been evaluated using piece-wise polynomials of temperature. The burning of isolated spherical particles in a mixed convective environment at atmospheric pressure has been simulated for various particle sizes, free-stream velocities and ambient temperatures. The numerical predictions have been compared with experimental results obtained using the porous sphere technique and the agreement is found to be good. Correlations have been developed for the critical Reynolds number at which transition from the envelope to wake flame occurs and also for the mass burning rates at sub-critical or super-critical Reynolds number regimes. It is observed that, at higher ambient temperatures, transition to wake flame is delayed to a higher critical Reynolds number value. The infinite rate chemistry model predicts flame shapes and mass burning rates with reasonable accuracy in the sub-critical Reynolds number regime, but it fails to predict transition to wake flame shape. For analyzing transition phenomena, a finite rate chemistry model is required. © 2005 Elsevier Ltd. All rights reserved.

International Journal of Heat and Mass Transfer

Flame shapes and burning rates of spherical fuel particles in a mixed convective environment

The combustion of a fuel droplet in a mixed convective environment has been simulated both theoretically and experimentally. In the theoretical model, the flow and transport equations have been solved subject to the assumptions of constant properties (except for density) and infinite rate kinetics, using the finite element method. The gas density has been treated as a variable, only to determine the buoyancy force contribution, and it has been evaluated assuming an ideal gas mixture. A porous-sphere facility has been employed for simulating the burning characteristics of a fuel droplet experimentally. The effects of airflow rate and droplet size have been studied for both upward and downward airflow configurations. Theoretical predictions for the mass burning rate and flame shape are in excellent agreement with the experimental results of the present study and also those reported in the literature. For upward airflow configuration, the mass burning rate is under-predicted by 15 to 20 percent when buoyancy effects are neglected. For downward airflow configuration, the flame shape is similar to the case of upward airflow for low air velocities. For higher downward air velocities, a flattened cylindrical flame front is obtained due to the opposing natural convection and forced convection flow fields, which has been predicted successfully. A detailed parametric study involving the variation of Reynolds number, ambient temperature and ambient oxygen concentration has also been carried out.

Combustion of a fuel droplet in a mixed convective environment

Proceedings of the Combustion Institute

Experimental and kinetic modeling study of extinction and ignition of methyl decanoate in laminar non-premixed flows

Combustion and Flame

Detailed chemical kinetic oxidation mechanism for a biodiesel surrogate

Investigation of combustion characteristics of biodiesel and its blends

Journal	Combustion Science and Technology
ISSN	00102202
Open Access	No