Abstract
The present work investigated the flame structures and oscillations of oxy-fuel combustions in a heavy oil boiler using OH planar laser-induced fluorescence imaging. Combustion instabilities, such as flame oscillation and combustion fluctuation, can assess the performance of an industrial burner in the boiler. The peak position variation in OH concentration was associated with the change of the reaction zone that corresponded with the fluctuation of the heat-release zone in the combustion chamber, which provides a valuable reference for the design of the combustion chamber. The experimental results suggest that the phenomenon of stratified flame combustion is related to the characteristic of flame oscillation. The substitution of N2 with CO2 will not significantly influence the flame oscillation frequency but increases the number of flame surface. As O2 concentration increased in the O2/CO2 atmosphere, the phenomenon of stratified flame combustion disappeared, and the flame presented an island-like structure. The bimodal oscillation of the combustion center was demonstrated by means of the probability density method; CO2 played a role in the extension of the combustion center. The combustion fluctuation of inner regions was quantitatively described; CO2 could maintain interregional stabilization to some extent. Compared with traditional measurement methods, PLIF technology has great advantages in evaluating burner performance and optimizing the design of the combustion chamber.
Highlights
In the context of energy saving and emission reduction, heavy oil, which has the advantages of abundant reserves and low costs, has been the focus of much attention [1,2,3]. e oxy-fuel combustion process has been proposed as a promising technology for controlling CO2 emissions, presenting an important option to address the environmental issues [4,5,6]. erefore, the combustion system of heavy oil is combined with oxy-fuel combustion process in order to reduce carbon dioxide emissions while offering a more efficient use of heavy oil resources [7]
High-speed PLIF visualization measurement technology possesses the characteristics of high spatial and temporal resolution, which can present the spatial structure of flame and provide the time characteristic information of flame. e peak position variation in OH concentration was associated with the change of the reaction zone that corresponded with the fluctuation of the heat-release zone in the combustion chamber. e flame fluctuation can be tracked in real time, so combustion instability reflected by flame fluctuation can be investigated without spatial and temporal limitations
The high-speed PLIF measurement system has been widely used in laboratory small-scale combustion devices [22, 23], but its application in industrial combustors bench, such as scramjet engines and boilers, is still rare [24, 25]. e harsh bench test environment and high requirements on the performance of laser, detector, and optical system limit its engineering applications
Summary
Previous experience with the study of industrial combustors suggests that combustion instability may exist in scramjet engines and gas turbines [9,10,11,12]. Both the type of fuel and the injection mechanism have an impact on acoustic motion and flame oscillation. The high-speed PLIF (planar laserinduced fluorescence) measurement system has been widely used in laboratory small-scale combustion devices [22, 23], but its application in industrial combustors bench, such as scramjet engines and boilers, is still rare [24, 25]. The flame structure of oxy-fuel combustion of heavy oil was reported applying a 400 Hz OH-PLIF. A deep understanding of the combustion instabilities is beneficial to understand comprehensively the operating performance of industrial burner, especially providing a valuable reference for boiler design
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