Temperature and Motion Tracking of Metal Spark Sprays

The temperature, velocity, and size of hot metal sparks are essential to understanding their ability to ignite flammable materials. However, existing measurement methods have limitations to achieve detailed, in situ measurements of these parameters. This paper describes a methodology that combines color-ratio pyrometry and particle streak tracing velocimetry, together with digital image processing to obtain non-intrusive measurements of the temperature, velocity, and size of multiple sparks in a spray. Furthermore, these measurements can be performed using a properly calibrated commercially available color digital camera. The principle of the measurement is firstly introduced, and the repeatability and accuracy of the method are validated via a designed experiment. Then the method is performed to measure the temperature and velocity of metal (steel) sparks in sprays generated by abrasive cutting. Measurements of initial spark temperatures and velocities are reported, as well as the evolution of the temperature and velocity along the flight path of the sparks. Observed initial spark temperature in this work mostly ranged within 1500°C to 1700°C. Results show evidence of both melting and oxidation of the sparks. Different blade speeds are used to understand their effect on spark velocity and temperature. The results of this study can be used as input parameters for spark oxidation and transport models, which in turn can be used to assess the hazards of spark sprays in wildland spot fires, ignition, explosions of flammable gaseous mixtures and dust clouds, and for monitoring and optimizing the material processes such as thermal-spray coating.