Diagnostics

Members of the UW Fire Research Group are involved in development and application of LIF and PLIF to reacting and non-reacting flows. Recent research efforts include the application of PLIF to measurement of joint velocity-scalar fields in large helium plumes and for visualization of nozzle flows in welding applications.

Helium plumes

This research was undertaken in partnership with Sandia National Laboratories, NM with the aim to collect a set of validation quality data appropriate for comparison with velocity and scalar statistics predicted using large computational fire models. The experiments were conducted in the Sandia FLAME facility, Albuquerque, NM with participation of UW researchers. After characterization of the facility, Particle Image Velocimetry (PIV) and PLIF were applied to measure joint velocity-concentration statistics in 1 m diameter helium plumes. Plumes were seeded with acetone to facilitate concentration measurements, and with glass microspheres as seed particles for PIV. A UV laser beam, expanded into a 1 m high sheet, was passed through the central plane of the plume, generating a fluorescence signal proportional to the acetone concentration in the plume. Using two high speed motion picture cameras, the fluorescence signal was captured on one film simultaneously with the PIV signal on the other. Film images were digitized and analysed using custom methods developed jointly by researchers at Sandia and the UW Fire Research Group.

In a complementary set of experiments in the same facility, PIV and PAH-fluorescence were employed to map velocity fields and reaction zone positions in 1 m diameter hydrogen and methane fires in quiescent environments.

This research was partially undertaken at FLAME facility at Sandia National Labs in Albuquerque, NM.

Research into the PIV diagnostic method is aimed toward developing new algorithms for application of PIV to flows in which there are large spatial gradients in velocity. Limitations in existing analysis methods were identified and new approaches developed to track, measure and validate the displacements of individual seed particles and particle clusters in the flow field. An iterative, probability-based particle correspondence framework was then proposed that allowed improved discernment of displacement gradients within a field. Comparative results based on a set of vortical flow situations indicated that the new methodology could provide improved particle tracking for flows in which there are strong gradients.

The nature of laminar non-premixed methane-air flames is studied over the pressure range of 0.5 to 4 MPa using a new high pressure combustion chamber outfitted with Spectral Soot Emission (SSE) and Line-Of-Sight Attenuation (LOSA) diagnostics for measurement of radially resolved soot volume fraction and soot temperature. The experiments are designed to develop improved diagnostics applicable in high pressure flame studies, as well as to improve understanding of the influence of pressure on soot formation. Improved soot formation, growth and oxidation mechanisms that incorporate the influence of pressure have wide applicability in the design and modelling of practical combustion systems operating at elevated pressures. With increasing awareness of the effects of particulates on health and the environment, as well as new legislation on particulate emissions, there is a need to study the physics of soot formation in order to develop strategies and designs to reduce soot emissions from practical combustion systems.

This research was conducted in collaboration with Prof. Ö. Gülder at University of Toronto Institute for Aerospace Studies (UTIAS) and Drs. G. Smallwood, D. Snelling and K. Thomson at NRC-ICPET.

Experimental studies were undertaken to investigate the shielding gas characteristics of various welding nozzle designs. Qualitative (smoke visualization and PLIF) and quantitative (PIV) imaging and analysis of existing welding nozzle designs were performed in order to determine the important parameters that affect the shielding gas behaviour in the nozzle passages, as well as in the flow immediately upon exiting the nozzle, under both cold flow and live welding conditions. It was found that nozzle geometry, shielding gas flow rate, contact tip position and internal gas diffuser configuration were important in the optimization of welding nozzle design. The results obtained from these parametric studies were used in developing new nozzle designs with improved shielding gas flow characteristics.

This research was conducted in collaboration with Tregaskiss Ltd. through the NRC-IRAP Program.