Experimental Investigations on Lifted Spray Flames for a Range of Coflow Conditions

Abstract

In the present work, the effect of coflow conditions and fuel injection pressure on flame lift-off height, flame stabilization, and flame fluctuations in liquid spray flames has been experimentally investigated for three different coflow cases: (1) cold flow, (2) cold flow with nitrogen dilution, and (3) preheated and diluted coflow. It has been observed that the flame lift-off height is proportional to the coflow velocity and inversely proportional to the injection pressure. The dependence of flame lift-off height on the fuel mass flow rate has been investigated using fuel injectors of identical spray cone angles, mean droplet diameter, and different fuel mass flow rates. It has been observed that the flame lift-off height decreases with an increase in the fuel flow rate. Mean droplet diameter (SMD) has a dominating effect on flame lift-off height and flame stability. An increase in the SMD increases the fluctuations in the stabilization point of the lifted flame and vice versa. For N2 dilution cas, (21%–17% O2 in coflow stream), the lift-off height increases with dilution as compared to ambient air coflow. The flame blows-off at lower coflow velocities due to reduced oxidizer concentration in the coflow. Preheating of the coflow stream enhances the droplet evaporation rate and mixing, thus leading to a significant increase in the stability of lifted spray flames.