Jihang Li - Academia.edu (original) (raw)
Papers by Jihang Li
Journal of Engineering for Gas Turbines and Power, 2021
Pilot flames are commonly used to extend combustor operability limits and suppress combustion osc... more Pilot flames are commonly used to extend combustor operability limits and suppress combustion oscillations in low-emissions gas turbines. Combustion oscillations, a coupling between heat release rate oscillations and combustor acoustics, can arise at the operability limits of low-emissions combustors where the flame is more susceptible to perturbations. While the use of pilot flames is common in land-based gas turbine combustors, the mechanism by which they suppress instability is still unclear. In this study, we consider the impact of a central jet pilot on the stability of a swirl-stabilized flame in a variable-length, single-nozzle combustor. Previously, the pilot flame was found to suppress the instability for a range of equivalence ratios and combustor lengths. We hypothesize that combustion oscillation suppression by the pilot occurs because the pilot provides hot gases to the vortex breakdown region of the flow that recirculate and improve the static, and hence dynamic, stabi...
2017 American Control Conference (ACC), 2017
This paper proposes a Bayesian nonparametric method for detecting thermoacoustic instabilities in... more This paper proposes a Bayesian nonparametric method for detecting thermoacoustic instabilities in gas turbine engines in real-time, where the underlying algorithms are formulated in the symbolic domain and the resulting patterns are constructed from symbolized pressure measurements as probabilistic finite state automata (PFSA) that is built upon a finite-memory Markov model, called D-Markov machine. The Bayesian nonparametric structure is adopted for: (i) automated selection of parameters in the D-Markov machine, and (ii) online sequential testing, to provide a data-driven and coherent statistical analysis of combustion instability phenomena without relying on numerically intensive models of combustion dynamics. The proposed method has been experimentally validated on the time series generated from a laboratory-scale combustion apparatus. The results of instability prediction, derived from the time series, have been compared with those of other existing techniques.
Volume 4B: Combustion, Fuels, and Emissions, 2019
The effect of a fully-premixed pilot flame on the velocity-forced flame response of a fully premi... more The effect of a fully-premixed pilot flame on the velocity-forced flame response of a fully premixed flame in a single-nozzle lean-premixed swirl combustor operating on natural gas fuel is investigated. Measurements of the flame transfer function show that as the percent pilot is increased there is a decrease in the flame transfer function gain at all frequencies, a decrease in the frequencies at which the gain minima and maxima occurred, and a decrease in the flame transfer function phase at high frequencies. High-speed CH* chemiluminescence flame imaging is used to gain a better understanding of the mechanism(s) whereby the pilot flame affects flame dynamics and thereby the flame transfer function. Time-averaged flame images show that the location of the maximum heat release rate does not change with forcing frequency or percent pilot, although the flame extends further upstream into the inner shear layer with increasing percent pilot. Heat release rate fluctuation images show tha...
2016 American Control Conference (ACC), 2016
This paper proposes a framework for analyzing video of physical processes as a paradigm of dynami... more This paper proposes a framework for analyzing video of physical processes as a paradigm of dynamic data-driven application systems (DDDAS). The algorithms were tested on a combustion system under fuel lean and ultra-lean conditions. The main challenge here is to develop feature extraction and information compression algorithms with low computational complexity such that they can be applied to real-time analysis of video captured by a high-speed camera. In the proposed method, image frames of the video is compressed into a sequence of image features. Then, these image features are mapped to a sequence of symbols by partitioning of the feature space. Finally, a special class of probabilistic finite state automata (PFSA), called D-Markov machines, are constructed from the symbol strings to extract pertinent features representing the embedded dynamic characteristics of the physical process. This paper compares the performance and efficiency of three image feature extraction algorithms: Histogram of Oriented Gradients, Gabor Wavelets, and Fractal Dimension. The k-means clustering algorithm has been used for feature space partitioning. The proposed algorithm has been validated on experimental data in a laboratory environment combustor with a single fuel-injector.
Research Journal of Applied Sciences, Engineering and Technology, 2013
The thermal loss angle error analysis and maximum pressure determination method analysis were con... more The thermal loss angle error analysis and maximum pressure determination method analysis were conducted first. Then the polytropic exponent method, the inflection point analysis, the loss function method and the symmetry method were utilized under different rotating speed, load and cooling water temperature, to calculate TDC in D6114 diesel engine and the results were compared with TDC position measured under the same condition with direct method of measurement. The study proved that (1) thermal loss angle of the diesel engine ranges from-1.0 ~-0.6°CA; (2) Thermal loss angle is mainly affected by rotating speed and is reducing when rotate speed increases;(3) the symmetry method is generally the optimum for calculating the thermal loss angle of automotive diesel engines, with an error within 0.2°CA.
Journal of Engineering for Gas Turbines and Power, 2021
Pilot flames are commonly used to extend combustor operability limits and suppress combustion osc... more Pilot flames are commonly used to extend combustor operability limits and suppress combustion oscillations in low-emissions gas turbines. Combustion oscillations, a coupling between heat release rate oscillations and combustor acoustics, can arise at the operability limits of low-emissions combustors where the flame is more susceptible to perturbations. While the use of pilot flames is common in land-based gas turbine combustors, the mechanism by which they suppress instability is still unclear. In this study, we consider the impact of a central jet pilot on the stability of a swirl-stabilized flame in a variable-length, single-nozzle combustor. Previously, the pilot flame was found to suppress the instability for a range of equivalence ratios and combustor lengths. We hypothesize that combustion oscillation suppression by the pilot occurs because the pilot provides hot gases to the vortex breakdown region of the flow that recirculate and improve the static, and hence dynamic, stabi...
2017 American Control Conference (ACC), 2017
This paper proposes a Bayesian nonparametric method for detecting thermoacoustic instabilities in... more This paper proposes a Bayesian nonparametric method for detecting thermoacoustic instabilities in gas turbine engines in real-time, where the underlying algorithms are formulated in the symbolic domain and the resulting patterns are constructed from symbolized pressure measurements as probabilistic finite state automata (PFSA) that is built upon a finite-memory Markov model, called D-Markov machine. The Bayesian nonparametric structure is adopted for: (i) automated selection of parameters in the D-Markov machine, and (ii) online sequential testing, to provide a data-driven and coherent statistical analysis of combustion instability phenomena without relying on numerically intensive models of combustion dynamics. The proposed method has been experimentally validated on the time series generated from a laboratory-scale combustion apparatus. The results of instability prediction, derived from the time series, have been compared with those of other existing techniques.
Volume 4B: Combustion, Fuels, and Emissions, 2019
The effect of a fully-premixed pilot flame on the velocity-forced flame response of a fully premi... more The effect of a fully-premixed pilot flame on the velocity-forced flame response of a fully premixed flame in a single-nozzle lean-premixed swirl combustor operating on natural gas fuel is investigated. Measurements of the flame transfer function show that as the percent pilot is increased there is a decrease in the flame transfer function gain at all frequencies, a decrease in the frequencies at which the gain minima and maxima occurred, and a decrease in the flame transfer function phase at high frequencies. High-speed CH* chemiluminescence flame imaging is used to gain a better understanding of the mechanism(s) whereby the pilot flame affects flame dynamics and thereby the flame transfer function. Time-averaged flame images show that the location of the maximum heat release rate does not change with forcing frequency or percent pilot, although the flame extends further upstream into the inner shear layer with increasing percent pilot. Heat release rate fluctuation images show tha...
2016 American Control Conference (ACC), 2016
This paper proposes a framework for analyzing video of physical processes as a paradigm of dynami... more This paper proposes a framework for analyzing video of physical processes as a paradigm of dynamic data-driven application systems (DDDAS). The algorithms were tested on a combustion system under fuel lean and ultra-lean conditions. The main challenge here is to develop feature extraction and information compression algorithms with low computational complexity such that they can be applied to real-time analysis of video captured by a high-speed camera. In the proposed method, image frames of the video is compressed into a sequence of image features. Then, these image features are mapped to a sequence of symbols by partitioning of the feature space. Finally, a special class of probabilistic finite state automata (PFSA), called D-Markov machines, are constructed from the symbol strings to extract pertinent features representing the embedded dynamic characteristics of the physical process. This paper compares the performance and efficiency of three image feature extraction algorithms: Histogram of Oriented Gradients, Gabor Wavelets, and Fractal Dimension. The k-means clustering algorithm has been used for feature space partitioning. The proposed algorithm has been validated on experimental data in a laboratory environment combustor with a single fuel-injector.
Research Journal of Applied Sciences, Engineering and Technology, 2013
The thermal loss angle error analysis and maximum pressure determination method analysis were con... more The thermal loss angle error analysis and maximum pressure determination method analysis were conducted first. Then the polytropic exponent method, the inflection point analysis, the loss function method and the symmetry method were utilized under different rotating speed, load and cooling water temperature, to calculate TDC in D6114 diesel engine and the results were compared with TDC position measured under the same condition with direct method of measurement. The study proved that (1) thermal loss angle of the diesel engine ranges from-1.0 ~-0.6°CA; (2) Thermal loss angle is mainly affected by rotating speed and is reducing when rotate speed increases;(3) the symmetry method is generally the optimum for calculating the thermal loss angle of automotive diesel engines, with an error within 0.2°CA.