الفهرس 
الغلافOnly 14 pages are availabe for public view
 |  | from | 128 |  |  |
| | | from | 128 | | |
Abstract
ABSTRACT
The demand for sustainable feedstock continuous to increase to limit the greenhouse gas emission issuing from petroleum fuels. In the way to switch to sustainable fuels, liquefied petroleum gas (LPG) is one of the better alternative fuels to reduce gaseous emissions. Most of the experimental work on the fundamental understanding of the combustion behavior of LPG fuel has been carried out in inverse diffusion flame burners.
Inverse diffusion flame (IDF) characterizes the features of both premixed and diffusion flames including wider stability limits, lower pollutants, and safer in operation. Moreover, the IDF is cleaner and more resistant to the lift-off and flashback phenomena. The present work aims at providing an experimental study on an inverse diffusion LPG flame issuing from an elliptical burner with an aspect ratio of 2:1. The changes in the flame appearance and mean gas temperature associated with the varying central air velocities, inner-to-outer air ratio, and outer elliptical tube angles at constant total air flow rate and with fixed thermal input are investigated. Both visual and shadowgraph images for different flames under different operating conditions were acquired. Axial and radial temperature distributions are conducted.
The investigation has focused on the flame stability limits which relying on central air velocity at a constant fuel velocity. The stability mapping of the IDF elliptic burner shows that the flame exhibits four zones namely yellow flame, blue flame, local flame extinction and re-ignition, and main flame extinction. For all flames, the air velocity of 22m/s is the starting limit of local flame extinction and re-ignition.
Three different measuring techniques are employed throughout the whole experimental program. These include, (i) a high-resolution digital camera for flame visualization, (ii) the shadowgraph imaging is acquired by 405 nm laser diode (UV laser), and (iii) the mean gas temperature is accomplished by a bare 125 µm (Pt-10% Rh) thermocouple (type-S).
The experimental results indicated that all flames exhibit dual flame structure. With increasing the central air velocity within 13.26 to 17.9 m/s at fixed fuel velocity, the flame becomes thinner and shorter due to better fuel entrainment. It is observed that the flame becomes longer and resembles a normal diffusion flame with increasing the outer air percentage from 0 to 50% because of the decreased air jet potential core momentum. With increasing the outer elliptic tube angle, θ within 0o to 90o, a slight change in flame length and less luminosity is found due to the fixed inner air flow rate.
The maximum centerline temperature falls with higher air velocities. Due to the elliptical shape of the fuel port, the radial temperatures at minor plan are higher than that on the major plan. That is attributed to the unequal fuel distribution around the air jet for the case with 100% inner air. Axial and radial temperature distributions show that with decreasing the outer-to-inner air ratio, the combustion process intensifies. That is attributed to the effect of axis switching of the outer air elliptic flow. For the influence of increasing the outer elliptic tube position angle on the thermal structure of IDFs, it is observed that the temperature along the centerline is not affected, and the air/fuel mixing is enhanced.