Typical spray formation process
- We consider an air-blast atomizer to illustrate the spray formation process.
Spray cone angle
- Spray cone angle dictates the mass distribution in spray.
- Combustor diameter is chosen based on the spray cone angle.
- Larger cone angle will result in the flame moving towards the periphery, heating up the combustor wall, which may lead to loss of thermal efficiency (due to heat loss from the wall rather than to the exit gases).
- Photography and image processing are widely used to estimate cone angle.
Spray patternation
- Patternation is one way of determining the spray mass distribution and degree of symmetry, by obtaining information on spray distribution from optical imaging.
- Optical methods are non-intrusive and can be adapted to collect data on-line.
- To define spray characteristics quantitatively, circumferential pattern analysis is expressed in terms of spray uniformity index (SUI).
Schematic of arrangement for image analysis
Spray uniformity index (SUI)
- Measure of the mass distribution within spray.
- Measures the standard deviation of the normalized total scattering per sector (m x n) from the mean.
- Here, n is the number of rows, m is the number of columns, Is is the local intensity and is the mean intensity for all rows and columns.
- Indicates spray uniformity.
- Normally, a lower value of SUI and a higher value of (Min/Max) intensity ratio express a more uniform spray pattern.
