Figure 1(a) shows schematic of the ‘Box of Turbulence’ rig which is used to generate statistically stationary zero-mean homogeneous and isotropic turbulence (HIT) at the central volume of the box under atmospheric conditions. The HIT is achieved by high-efficient mixing of arrays of synthetic air jets. As depicted in the below figure, the turbulence rig consists of three pairs of loud speakers arranged on aluminum rails in such a way that the loudspeakers in each pair are oppositely faced and directed towards the center. Rubber pads were kept between speakers and back plate for vibration isolation. Perforated plates containing a two-dimensional array of 80 holes of 6 mm diameter (organized in a specific pattern) were fitted on top of each loud speakers such that operation of the loudspeakers generate high velocity synthetic turbulent jets from the surface of each plate. Each loud speaker was driven by a sine waves (frequency 50 Hz) generated by a 16 bit National Instruments analogous output card with eight channels out of which six channel are used in the current study. The signals from the output channel of the PCI card were amplified using three two channel amplifiers. Once actuated by the amplified signals, each loudspeaker generate an array of synthetic jets. Because of the inherent tolerance limits in the output of all electronic devices, appropriate balancing of the input voltage to each speakers requires hit and trial method which was done by operating two ‘Master control’ knobs on each amplifiers to produce same velocity jets from all speakers. The synthetic air jets interfere at central region and as a result of mixing, the zero-mean isotropic turbulence is generated. Different turbulent intensity/kinetic energy can be realized at the center of the box by controlling the voltage input to the speakers via the ‘Master control’ knobs in the amplifiers. The air flow turbulence at the center of the box was characterized by two-dimensional digital Particle Image Velocimetry (PIV). Figure 1(b) shows a schematic of the plan view of the facility and the optical arrangements for PIV.

Setup to produce homogeneous and isotropic turbulence

Faculty incharge:

Srikrishna Sahu

Fig. 1 shows the Interferometric Laser Imaging for Droplet Sizing (ILIDS) for droplet size and velocity measurements, Fig. 2 shows the Particle Image Velocimetry (PIV) for fluid velocity, Fig. 3 shows the high speed imaging of sprays and Fig. 4 shows the Laser Induced Fluorescence (LIF) for liquid jet visualization.

Optical diagnostic techniques

Faculty incharge:

Srikrishna Sahu

Understanding the dynamics of gasification in a canonical configuration is essential for reactor design and the counter-current flame propagation mode in a packed bed offers one such with the following advantages - (1) fuel flux, as a function of superficial velocity exhibits universal characteristics with distinct regimes (gasification and combustion), (2) tar fraction in product gases under counter-current configuration is much less compared to co-current (updraft) systems and hence a preferred configuration for downdraft gasifiers, small (cooking) and medium scale (industrial heating) systems, (3) flame propagation in these practical configurations is analogous to packed bed systems with a coordinate frame fixed to the unburnt fuel, and (4) single particle models developed using packed bed systems can be extended to fluidized bed configurations as well. A 108 mm dia, 500 mm long counter-current packed reactor is operational in our lab; it is instrumented to measure flame propagation rate, fuel consumption rate and exit gas composition (using both NDIR based gas analyzer and a GC). The reactor is currently being used to measure the 'net-CO2 and steam' conversion potential of biomass.

Lab-scale counter-current biomass packed bed reactor

Faculty incharge:

S. Varunkumar

High ash content and low fusion temperature are the major bottlenecks in combustion and gasification of Indian coals. Inspired by the MILD combustion systems used for gaseous fuels, a reactor has been designed and developed in our lab for combustion and gasification of Indian coals. This configuration offers the following advantages - (1) stable primary flame even with low grade coal, (2) near homogeneous temperature distribution, and (3) modularity and easy scale up. The near homogeneous temperature distribution is achieved by creating an intense recirculation zone, like in MILD systems, using asymmetrical high speed secondary jets. The primary axial air carries the coal into the reactor. The reactor temperature can always be maintained lower than the fusion temperature by varying the ratio of primary to secondary air. Auxiliary systems are available for crushing, seiving and feeding of coal.

MILD inspired coal combustion/gasification burner

Faculty incharge:

S Varunkumar

Non-premixed flame established in the boundary layer of oxidizer flow past a porous cyclinder issuing fuel is commonly used for characterizing extinction. This configuration is known as the Tsuji burner. It was used extensively by Tsuji and co-workers from 1960 till 1980 to study extinction of non-premixed flames. Opposed jet configuration became the preferred choice after this point and extensive studies have been performed over the last four decades covering a wide range of fuel-oxidizer combinations. The principal reason for this transition is likely to be the dependence of measured extinction strain rate values on the diameter of the porous cylinder; that the flow is not strictly 1D in Tsuji type burner leading to flame curvature effects at smaller diameters and associated 2D effects on the measured extinction strain rates are the possible causes for this. Unlike this, the flames in opposed jet configuration are flat. But even here, the measured extinction strain rate is a function of nozzle separation distance. Preliminary 2D CFD simulations for opposed jet configuration have shown that there exist a nozzle separation distance L* where the extinction occurs at the same value of a_g for 1D and 2D computations. Therefore, experimental determination of a_g for validation of kinetic mechanisms using 1D framework requires a prior estimate of L* and hence inputs from 2D CFD and experimental results for the range of L. In the light of this, there is a possibility of using the much simpler Tsuji configuration for experimentally determining a_g, which can later be used for optimization of kinetic mechanisms using a combination of 1D and 2D numerical simulations. With this principal aim, a Tsuji burner has been developed in our lab; it is designed to accomodate different burner diameters ranging from 5 to 50 mm and is currently being used to study extinction characteristics of different gaseous fuels and its geometric dependence.

Tsuji type counter flow burner

Faculty incharge:

S. Varunkumar

The axisymmetric co-flow burner consists of two concentric tubes made of stainless steel. Metered quantities of fuel and air are supplied from radial inlets to a mixing chamber. The mixture, from the chamber is passed through a central core tube having 10 mm internal diameter. Surrounding this core tube, there is a co-flow tube of 42 mm internal diameter. Secondary air is supplied through this co-flow tube. Fine meshes are placed in the tube to filter eddies. This also helps in intercepting the flame, in case the flame flash backs into the tube.

Schematic of the co-flow burner set up

Faculty incharge:

V. Raghavan

The cross-flow set up mainly consists of a settling chamber, flow straighteners (honeycomb structure), a test section, air supply system and fuel supply system. Air is supplied perpendicular to the axis of the cylindrical settling chamber G through the path A-B-C-D. Rotameter used for air has been pre-calibrated for the required range of volumetric flow rate. The settling chamber has been constructed using mild steel and is of diameter 200 mm. It consists of a chamber of length 150 mm, to which the air is supplied, and another of length 300 mm. The chamber having a length of 300 mm facilitates the flow development and ensures a steady uniform flow at the exit of it and into the test chamber. To ensure uniform and unidirectional flow of air into the test section, a honeycomb flow straightener is present just before the exit of this chamber. Porous block is made of pressed glass wool. It has a length of 70 mm, width of 19mm and depth of 10 mm. Fuel mixture enters the test section uniformly with the desired volumetric flow rate (or an average velocity).

Schematic of the cross-flow setup with the details of the obstacles and the fuel injector

Faculty incharge:

V. Raghavan

The porous sphere set up consists of a liquid fuel feed system, wind tunnel and a porous alundum sphere. The porous sphere is prepared from white aluminium oxide and powdered fire clay. A stainless steel hypodermic needle of diameter 1.2 mm has been used to support the alundum sphere. Uniform distribution of fuel inside the porous sphere is ensured by drilling radial holes of 0.4 mm diameter at the end of the hypodermic needle. The other end of the needle is fixed to a glass syringe. An infusion pump is used to supply the fuel. The sphere is supported in front of an air flow system, which consists of a low turbulence wind tunnel of 200 mm diameter. Mass burning rate is measured by noting down the fuel flow rate (ml/h) from the syringe.

Schematic of the porous sphere experimental set up

Faculty incharge:

V. Raghavan

The cold free-jet test facility consists of a Khosla-Crepelle compressor,two storage tanks and pipeline system supplying compressed air to all rooms in the laboratory. The air is pressurized using a 150 HP 2-stage, inter-cooled reciprocating air compressor driven by a three phase induction motor. It can pressurize the air up to 8 bars absolute. The compressed air is stored in two separate storage tanks of total capacity of 20 m3. The compressed air is supplied to the experimental area from storage tanks through 4-inch plumbing.

Faculty incharge:

Srinivasan K