A study of droplet velocity and diameter measurements in a reacting diesel spray produced by a flow-blurring injector
In many combustion applications such as gas turbines, liquid fuel atomization is important to obtain lower emissions of nitrogen oxides (NOx), carbon monoxide (CO), unburned hydrocarbons (UHCs), and soot particles. Thus, understanding spray characteristics is essential for determining how fuel and air mix with each other and subsequently combustion takes place. In this experimental study, Phase Doppler particle analyzer (PDPA) and OH* Chemiluminescence (CL) imaging techniques are employed as a diagnostic technique to monitor the spray characteristics in the cold and reacting regions of a diesel spray flame using a flow-blurring (FB) injector. PDPA is a well-known technique to measure the diameter and velocity of spherical particles. PDPA is used in many research applications including fuel injection, spray, and combustion. PDPA system does not disturb the flow being measured, and thus, it is preferable over intrusive measurement techniques. A baseline case using a FB injector with a 3 mm orifice exit diameter and no inner slant is studied and operated at air to liquid mass ratio (ALR) of 2.0, heat release rate (HRR) of 60 kW, and equivalence ratio (φ) of 0.75. First, OH* chemiluminescence imaging is used to analyze the flame structure. Next, PDPA is used to acquire velocity and Sauter mean diameter (SMD) distributions in cold and flame regions. Then, a parametric study is performed by varying the ALR, and its influence on the diameter and velocity of the fuel droplets is investigated. The findings from OH* CL images suggest that as the ALR increases, the FB injector produces fine droplets and enhances secondary atomization to disintegrate the droplets further. Furthermore, the results show that FB injector produces finer droplets and mean axial velocity increases as ALR is increased. The Sauter mean diameter (SMD) and mean axial velocity decreases as the droplets enter the flame zone because heat released leads to droplet evaporation. Therefore, the larger droplets become finer whereas finer droplets are completely vaporized and mixed with the air.