الفهرس 
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Abstract
ABSTRACT
The generation of thermal energy from burning fossil fuels (solid, liquid, gas) for power generation, transportation, industrial applications remain to be almost the prime source (almost 80%) of nowadays usage. This situation appears to be alarming when considering their rapid depletion and the concern regarding the air quality deterioration associated with their burning. Current worldwide strategies and policies put priorities on (i) increasing the energy share of renewable resources (ii) efficient burning of fossil fuels including biofuels and/or their blends with conventional oil fuels, (iii) the adoption new combustion technologies as well as modifying burners design to mitigate the environmental pollution.
The present thesis is concerned with burning standalone biofuels (mainly waste cooking oil) and their blends with light and heavy diesel oils. The experimental program is divided into two main parts namely, (i) Hot measurements covering enclosed and free flame test cases and (ii) Cold measurements to characterize the interaction (at the macroscopic and microscopic level) between the fuel spray and the surrounding air.
In the former case an industrial disc stabilized coaxial burner fitted with a central twin air assisted atomizers (Delavan Siphon nozzle, solid cone) are employed. This burner is coaxially mounted on a cylindrical water-cooled combustor. The test cases cover varying excess air factor at a given input throughput for light and heavy diesel oils and their blends with waste cooking oil at a fixed blending ratio (on mass basis) of 20%. The measurements include the inflame mean gas temperature, as measured by a 50 μm bare wire thermocouple and the cumulative heat transfer to the cooling jacket. The experimental program of these hot test cases is extended to define the flame regimes (for the free flames) at the microscopic level of the cross-sectional average values of the C2 and CH radicals as well as the flame temperature using a hyperspectral camera.
The cold experiments are intended to characterize the standalone spray flow field in free atmosphere for the tested fuels and the interaction between the spray cone and the coaxial outer secondary air. The later is conducted for two burner configurations namely, (a) the burner fitted with a stabilizer disc and (b) the burner fitted with coaxial vane air swirlers having a swirl angle of (0, 15,30, 40 and 60O). Extensive experiments are conducted that cover the variations of the spray flow field at different secondary air flow rate whereby the air / liquid ratio of the atomizer is varied at any case. The measurements include at the macroscopic level: the spray visual image, the spray cone angle, the spatial distributions of the spray concentration along the spray (using a patternator) and the estimated vaporization rate (derived from the variations of the spray concentration). The PIV is employed to provide measurements (at the microscopic level) of the variations of the spray flow field in terms of droplet size, fuel droplets velocity and their streamline trajectories
The variations in the cold spray patterns with the changes of the secondary air swirl conform to the well-known four flame configurations previously reported by the International Flame Research Foundation (IFRF), and hence provide detailed insight into the spray/air interaction for adequate development of computational modeling.
The non-reacting study covers and gives good agreement with all spray patterns that are mentioned by International Flame Research Foundation (IFRF). The cold study shows four sections where a free spray at stagnant air and another with annular co-flowing air. The blended fuel spray possesses a homogenous droplet velocity distribution along the spray when compared with diesel and waste cooking oil sprays.
The non-reacting flow field associated with the employment of the stabilizer disc exhibits three successive regions along the spray development. The first region is located at the immediate vicinity of the burner exit that encompass an inner core whereby the fuel jet spreads and penetrates the central recirculation zone being created by stabilizer disc, a surrounding shear layer resulting from the central primary air jet and an outer recirculation zone. The second intermediate region where the spray jet continue expansion at a lower velocity causing progressive spreading and vaporization of the fuel droplets that leads to the formation of an outer envelope of homogeneous cloud of fuel/air vapors. The last region is located at the far end where the remaining finer droplets continue vaporization and spreading at a slower pace. The increase of the secondary air velocities increases the strength of the recirculation zone, and so results in increasing the vaporization rate, squeezing the fuel jet core spreading while increasing the width of the outer foggy envelop.
The employment of vaned air swirlers dramatically promotes the spray vaporization rate and spreading. Low swirl number, SN < 0.3, gives longer jet penetration, lower vaporization rate and narrower spreading. Intermediate swirl numbers, 0.3 < SN < 0.54, give shorter penetration, higher droplet velocities at immediate burner exit and concentrated vaporization at the central core. Higher swirl number, SN > 0.54, results in higher angular momentum, disappearance of jet penetration and wider spreading.