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Abstract
To evaluate the effects of inlet pressure on the ignition process of spray combustion, the images of the ignition process were recorded and the outlet temperatures were measured under inlet pressure of 0.04–0.16 MPa. The initial flame formation and flame propagation and the effects of the inlet pressure on the initial flame formation were observed. A variation of outlet temperature, flame propagation, initial time of outlet temperature rise, time of maximum temperature rise, and temperature rise rate was investigated. With increasing inlet pressure, the time of initial flame formation and time of maximum area growth rate of flame decrease and the centroid location move radially. The radial distances of the initial flame centroid gradually increased by about 13%, 5%, 6%, 12%, 57%, and 24%. The trace of flame centroid is determined from the distribution of fuel and is related to the initial SMD of the atomizer. The maximum temperature rise and temperature rise rate are determined by the rate of flame chemical reaction, rate of large drop evaporation, and fuel/air ratio. With increasing inlet pressure, the maximum temperature rise increased by 50%, 58%, 12%, 11%, and −9%, respectively. Meanwhile, the rate of the temperature rise increased by about 47%, 54%, 11%, 11%, and −7%, respectively.
Highlights
Spray combustion devices are widely used in many fields
Based on the growth rate of the flame area, the ignition process in the combustion chamber can be divided into three phases: (i) the formation phase of the initial flame, (ii) the high-speed development phase of the flame, and (iii) the stable development phase of the flame
The formation time and location of the initial flame determine the starting time of the temperature rise of the thermocouples located at the combustion chamber exit and the difference in the starting times of the temperature rise of the thermocouples located at different radial positions
Summary
Spray combustion devices are widely used in many fields. The fuel is directly injected into the air flow, and the ignition is a complex process including the evaporation and blending of fuels. Continuous shooting of flame images by a high-speed camera is an effective method to study the ignition process. Marchione and Mastorakos [11, 12] experimentally studied the ignition process and ignition characteristics of spray combustion of n-heptane. Ahmed and Mastorakos [2,3,4] studied the ignition process of a methane jet and found that the flame propagated upstream in the shape of a cylindrical surface after the initial flame kernel was formed. The ambient pressure has been mostly affected on ignition such as fuel atomization [15,16,17,18,19,20], minimum ignition energy [21,22,23,24], flame kernel propagation speed [25], and burning velocity [26].
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