Yong Mu

Experimental Investigation of Performance of an Air Blast Atomizer by Planar Laser Sheet Imaging Technique

It is widely recognized that the fuel/air mixing process is a critical factor in improving combustion efficiency and in minimizing pollutants such as NOx. Enhancement of fuel/air mixing can lead to lower pollutant emissions and greater efficiency. However, swirling flows in lean combustors play the role of fuel/air mixing and flame stability. The complex fluid dynamic phenomena encountered in swirling two-phase flow contribute to the difficulty in complete understanding the different processes occurring in combustors. Fortunately, Optical and laser-based visualization techniques available in our lab are important non-intrusive tools for visualizing flow process, especially for fuel injection and fuel/air mixing. To provide for a better understanding of effects of counter-rotating flow on droplets in atomization process, this study is a detailed characterization of the spray generated by an airblast atomizer by planar laser sheet imaging method.Optical facility for spray diagnostics with fuel Planar Laser Induced Fluorescence (fuel-PLIF) method for fuel distribution, and Particle Image Velocity (PIV) method for velocity of droplets, is used to evaluate the performance of an air-blast atomizer. The results show that the performance of secondary atomization is influenced by swirling flow and primary atomization simultaneously, the swirling flow exhibits significant influence on the droplet size and space distribution relative to that of primary atomization. The primary swirling air reopens the spray cone generated by pressure-swirl atomizer, and the secondary swirling air affects the fuel distribution by forming the recirculation zone. The results provide critical information for design and development of combustion chamber.Copyright

Effect of Fuel Staged Proportion on NOX Emission Performance of Centrally Staged Combustor

The low NOX emission technology has become an important feature of advanced aviation engine. A wide range of applications attempt to take advantage of the fact that staged combustion operating under lean-premixed-prevaporized (LPP) conditions can significantly decrease pollution emissions and improve combustion efficiency. In this paper a scheme with fuel centrally staged and multi-point injection is proposed. The mixing of fuel and air is improved, and the flame temperature is typically low in combustion zone, minimizing the formation of nitrogen oxides (NOX), especially thermal NOX. In terms of the field distribution of equivalence ratio and temperature obtained from Computational Fluid Dynamics (CFD), a chemical reactor network (CRN), including several different ideal reactor, namely perfectly stirred reactor (PSR) and plug flow reactor (PFR), is constructed to simulate the combustion process. The influences of the pilot equivalence ratio and percentage of pilot/main fuel on NOX and carbon monoxide (CO) emissions were studied by Chemical CRN model. Then the NOX emission in the staged combustor was researched experimentally. The effects of the amount of pilot fuel and primary fuel on pollution emissions were obtained by using gas analyzer. Finally, the effects of pilot fuel proportion on NOX emission were discussed in detail by comparing predicts of CRN and experimental results.Copyright

Improvement on ignition and lean blowout performances of a piloted lean-burn combustor

This work focuses on optimizing the flame stability by matching the primary spray with swirling air streams in swirl cup which is used as pilot stage of a lean-burn fuel injector. Two configures of pressure-swirl atomizer for pilot spray have been investigated for their ignition and lean blowout (LBO) performances, the new designed pilot atomizer decrease fuel–air ratio (f/a) of the ignition limit by about 35%, and capability of LBO is greatly improved with decreasing fuel–air ratio from 0.015 to 0.005. Furthermore, in order to relate the pilot spray characteristics with the combustion performances, the performances of pilot pressure-swirl atomizer working both single and together with swirlers are carried out by optical spray diagnostics in a quiescent open air environment. Fuel planar laser induced fluorescence method for fuel distribution, particle image velocimetry method for velocity of droplets, and Fraunhofer diffraction technique for line-of-sight measurement of D32 are used to visualize the spray. The interactions between pilot spray and pilot, main swirling air streams are analyzed. The relative pressure loss of swirling air streams larger than 3% is recommended for this type of spray facility to make sure high quality of atomization at ignition and near LBO conditions. Improvements of ignition and LBO performances by optimizing the pilot spray illustrate that matching pilot spray with swirling air streams is an effective method to improve capability of stable combustion in fuel-staged multi-injection combustors.

Experimental and numerical study of the effect of main stage stratifier length on lean blow-out performance for a stratified partially premixed injector

The lean blow-out performance of the pilot flame in a stratified partially premixed injector is studied in this work considering the influence of the main stage stratifier length. Particle image velocimetry and kerosene planar laser-induced fluorescence experiments at nonreacting conditions were carried out to give an explanation of the combustion performance. The evolutions of spray and velocity in space are discussed in detail to find out the inherent correlations of combustion stability, spray distribution, and flow structures. Moreover, special attentions are paid to the variation of primary recirculation zone with the increase of the stratifier length and its driving factors. Specifically, by lengthening the stratifier of the main stage, the primary recirculation zone is enlarged both axially and radially, and this creates an advantageous flow topology for the anchoring of the pilot flame. Finally, the dominating mechanisms for the primary recirculation zone that are responsible for the alteration of the primary recirculation zone size are pointed out with the assistance of computational fluid dynamics.