Effects Of Airflow Temperature Research Articles

An experimental study on the influence of airflow temperature on the different silicone oil droplet breakup regimes

In industrial environments, droplet deformation and breakup in hot airflow are universal. The effect of airflow temperature (293–473 K) on the breakup of silicone oil droplets in continuous airflow was studied. The breakup morphology, deformation stage, and breakup regime map are discussed in detail by varying the airflow temperature and Weber number in this paper. The results show that the breakup regimes of silicone oil droplets are consistent with water droplets in the Weber number (5 < We < 30) considered in this paper. However, airflow temperature has an obvious effect on droplet breakup modes. The number of nodes generated at the toroidal rim of the silicone droplet is verified to be the same as that of the water droplet, following “the combined Rayleigh–Taylor /aerodynamic drag” mechanism. The rising airflow temperature will increase the droplet cross-stream diameter. The maximum cross-stream diameter relationship for droplet breakup at different temperature airflows is proposed. The liquid bag growth time can accurately describe the droplet breakup characteristics in a hot airflow environment. The correlation equation for the time characteristics is proposed. In addition, the droplet breakup angle is used to describe the space range of droplet breakup. Eventually, special attention is paid to sub-droplets. The airflow temperature has a considerable effect on the sub-droplets. The average number of sub-droplets and the average surface area ratio before and after breakup increased as the airflow temperature increased. However, the number of sub-droplets and surface area increase slowly after the airflow temperature increases to a certain level.

Effect of Airflow Temperature on the Formation of Initial Flame Kernel and the Propagation Characteristics of Flame

Using liquid RP-3 aviation kerosene as the fuel to study, the effect of airflow temperature on the formation of initial flame kernel during the ignition of spray combustion and on the propagation characteristics of flame was investigated. Combining high-speed camera and dynamic temperature acquisitions at the outlet of combustor, the internal triggering mode was used under a constant fuel flow rate and airflow velocity. This combined system simultaneously recorded the formation of initial flame kernel, flame propagation, and outlet temperature variation of combustor under different airflow temperatures. MATLAB software was used to obtain the reaction zones at different moments and to analyze the effects of airflow temperature on morphological characteristics such as flame area, perimeter-to-area ratio, maximum length-to-height ratio, equivalent mean length-to-height ratio, mass center, and centroid. According to the growth rate in flame area, the ignition process can be divided into three stages: formation of flame kernel, rapid development of flame, and stable development of flame. Airflow temperature not only affects the formation time of flame kernel but also affects the growth rate of flame area. During the development of flame, the movements of mass center and centroid are irregular, and their positions do not coincide with each other. However, the overall moving trends are consistent. With the increase of the airflow temperature, the position, where the flame kernel is gradually formed, moves closer to the center of the end face of spark plug. The force of airflow on flame is the main factor that increases the flame area and heat-release rate. Therefore, the folds around the flame edge mainly result from the stretching under the action of airflow. With the increase in airflow temperature, the heat release of the initial flame kernel increases, and the ratio of perimeter to area as a characterization parameter increases by 8%, 86%, and 33%, respectively. In addition, the maximum outlet temperature rise increased by about 53%, 73.5%, and 0.65%, respectively. Meanwhile, the maximum rate of temperature rise increased by about 42.8%, 57%, and 5.1%, respectively.

Ignition and flame-holding of H 2 and CH 4 in high temperature airflow by a plasma torch

The effect of airflow temperature on ignition characteristics of a plasma torch was experimentally investigated. Various combinations of fuels (CH 4 and H 2) and plasma jets (PJs) (N 2, O 2, and N 2/H 2) were tested for a wide range of airflow temperature from 300K to 700K and the PJ power required for ignition was investigated. Ignition by the PJ occurred more easily in a high temperature airflow than in an atmospheric temperature airflow. The main reason for this was considered to be the increase in the reactivity of the fuel at high temperature rather than the effect of radicals in the PJ, because there was no difference in the spectroscopic measurement of the PJ between T air = 300K and 700K. The addition of H 2 to the N 2 feedstock was also effective for ignition enhancement of both fuels (H 2 and CH 4). In particular, the H 2 30%/N 2 70% PJ was able to ignite both fuels even at atmospheric temperature and the lowest electric power input for the stable operation. One of the reasons for this advantage of the H 2 30%/N 2 70% PJ was the heat release from the diffusion flame of the H 2 included in the feedstock with the airflow after injection. Moreover, the conditions around the local ignition site such as the local fuel concentration or the size of the contact area of the PJ and the fuel jet were found to be important factors for the success of ignition.