Tonghun Lee's research while affiliated with University of Illinois, Urbana-Champaign and other places

Publications (151)

Article
Large-eddy simulations of stable and unstable ramjet operational modes are presented for an axisymmetric inlet-isolator-combustor configuration experimentally tested in the University of Illinois's ACT-II arc-heated combustion tunnel. A 32 species ethylene oxidation mechanism including nitrous oxide formation reactions is used in the calculations (...
Article
Modern aircraft compression ignition engines that seek to achieve fuel-flexible operation require ignition-assisting devices to perform reliably. Many military propulsion systems, and unmanned aircraft in particular, can use hot surface energy addition to improve engine performance. An analysis of the thermomechanical stress behavior of hot surface...
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Full-text available
This report outlines the establishment of distributed databases for management and integration of current and future aviation fuels. Aviation fuel property and performance data has been gathered for many years in public and company specific fuel surveys. These surveys are suitable for use as overall quality control information and for monitoring ch...
Article
Time-resolved concentrations of oxygen (O2), carbon dioxide (CO2) and water vapor (H2O) produced by controlled propane gas burners are measured at three locations in a residential structure equipped with a heating, ventilation and air-conditioning (HVAC) system. Experiments are conducted to assess the effects of HVAC operating status (off vs. on) a...
Article
In this work, the growth regime of combustion instability was studied by analyzing 10 kHz OH planar laser induced fluorescence (PLIF) images through a combination of dynamic mode decomposition (DMD) and spectral proper orthogonal decomposition (SPOD) methods. Combustion instabilities were induced in a mesoscale burner array through an external spea...
Conference Paper
View Video Presentation: https://doi.org/10.2514/6.2022-2337.vid PIV measurements were conducted in the Arc-Heated Combustion Tunnel (ACT-II), on a high enthalpy Mach 4.5 nozzle flow. The primary motivation of the current work is to establish the feasibility of PIV as a high-quality flow diagnostic technique in hypersonic arc-heated flows and produ...
Conference Paper
View Video Presentation: https://doi.org/10.2514/6.2022-2059.vid The flow and flame dynamics within liquid fueled gas turbine combustors are complex due to the interactions between the highly turbulent flow, spray dynamics and combustion. Computational tools help understand these governing processes. Near nozzle spray characteristics are particular...
Conference Paper
View Video Presentation: https://doi.org/10.2514/6.2022-0364.vid In the interest of developing small-scale gas turbine combustors, understanding liquid fuel spray effects on global combustion ignition performance is critical. In these experiments, baseline ignition performance behavior is established for a relatively small-scale gas turbine combust...
Conference Paper
View Video Presentation: https://doi.org/10.2514/6.2022-1255.vid Cetane number (CN) is a metric widely used to measure the performance characteristics of jet fuels. While it is a common parameter, the exact definition of cetane number is not easily correlated to typical combustion parameters that are measured through experiment such as gas phase ig...
Conference Paper
View Video Presentation: https://doi.org/10.2514/6.2022-1409.vid The fluid and combustion dynamics were experimentally studied in Mach 4.5 high-enthalpy flows using constant area scramjet models with the axisymmetric and the perisymmetric cross-sectional shapes. The perisymmetric shape is analogous to the axisymmetric, inspired to enhance the fuel...
Conference Paper
View Video Presentation: https://doi.org/10.2514/6.2022-0678.vid The heat transfer behavior of a high-temperature cylindrical heater is evaluated over a wide range of flow conditions in a circular cross section experimental facility. Hot surface heaters exhibit promising energy addition functionality to support multi-fuel operation in compression i...
Conference Paper
View Video Presentation: https://doi.org/10.2514/6.2022-0228.vid This paper investigates deep learning algorithms to aid the evaluation of sustainable aviation fuels (SAF) using comprehensive two-dimensional gas chromatography (GCxGC). Specifically, two tasks are addressed: 1) Detection of low-confidence fuels with novel chemical characteristics fr...
Conference Paper
View Video Presentation: https://doi.org/10.2514/6.2022-0225.vid The data-driven optimized mechanism has recently been proposed for chemical kinetic modeling of the combustion of real, multi-component fuels. Experimental datasets of ignition delay times across wide temperature and equivalence ratio ranges are obtained by using a rapid compression m...
Conference Paper
View Video Presentation: https://doi.org/10.2514/6.2022-1849.vid Large-eddy simulations of stable and unstable ramjet operational modes are presented for an axisymmetric inlet-isolator-combustor configuration experimentally tested in the University of Illinois’s ACT-II arc-heated combustion tunnel. A 32 species ethylene oxidation mechanism includin...
Conference Paper
Energy addition using a hot surface probe is required for reliable ignition of aircraft compression ignition engines running on fuel variations and at altitude conditions. Thus, durability of the hot surface probe is crucial for application in these engines. Thermo-mechanical stress is one of the key parameters that determine durability, which requ...
Article
Partial substitution of hydrocarbon fuel with hydrogen can effectively improve small-scale combustion system stability and performance, potentially opening the way for novel compact power generation and/or propulsion systems in the future. In this study, the effects of hydrogen enhancement between 0% and 40% hydrogen volumetric fractions in methane...
Conference Paper
View Video Presentation: https://doi.org/10.2514/6.2021-3615.vid Aircraft compression ignition (CI) engines, originally developed for ground applications, exhibit significant ignition problems due to various fuel compositions and reactivities encountered in the field. Energy addition via a hot surface ignition assistant is one potential remedy; how...
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Full-text available
This manuscript presents a study of hydrogen-enhanced methane flames in a compact mesoscale burner array, where even a minute addition of hydrogen can significantly improve flame stability with reduced combustion length scale thereby enabling volumetric flexibility in small-scale combustion systems. The effect of hydrogen enhancement is demonstrate...
Article
In this study, we demonstrate successful development of a predictive model that detects both the fuel-air equivalence ratio (ϕ) and local pressure prior to plasma formation via machine-learning from the laser-induced plasma spectra; the resulting model enables measurement of a wide range of fuel concentrations and pressures. The process of model ac...
Conference Paper
The effect of ignition assistant probe temperature on ignition delay was investigated to achieve reliable compression ignition engines in aircraft systems using numerical simulations of alcohol-to-jet (ATJ) fuel injected into a combustion chamber with a hot surface probe. The main goal of this study is to improve understanding of the interaction be...
Conference Paper
The autoignition characteristics of an alternative alcohol to jet (ATJ) fuel are examined by analyzing chemical ignition delay using a rapid compression machine (RCM) and shock tube. Additionally, a data-driven chemical kinetic mechanism based on the HyChem approach of ATJ is proposed for modeling the ignition process. Ignition delay times of ATJ a...
Conference Paper
Advancements in fuel efficiency and emissions reduction of commercial automotive vehicles as well as progress in the fuel flexibility of heavy-duty direct-injection natural gas (DING) engines demonstrate the utility of compression ignition (CI) engines in a wide range of engineering applications. However, the demand for a multi-fuel capable engine...
Conference Paper
As alternatively derived jet fuels become more common in the aviation industry, it is increasingly important to understand their lean blowout behavior as early as possible in the fuel development process. This work uses a small-scale research combustor (ARC-M1) to ascertain the lean blowoff behavior of a selection of conventional and research fuels...
Article
Nanosecond-gated laser-induced breakdown spectroscopy (n-LIBS) has been used to quantify fuel mole fraction (ΧC2H4) in the cavity flameholder of a model high-speed combustor. The measurement locations selected, in the vicinity of the cavity shear layer, have low fuel concentrations. Previous n-LIBS measurements showed unexpectedly high values at th...
Article
A data-driven chemical kinetic mechanism for the military version of Jet A, F-24, is developed for numerical simulations of the ignition process. The main purpose of this study is to obtain a practical F-24 mechanism across wide temperature and equivalence ratio ranges, with a particular focus on the negative temperature coefficient and low tempera...
Article
Fuel-flexible aircraft propulsion systems using compression ignition engines will require novel strategies for reducing the ignition delay of low-reactivity fuels to feasible timescales. Hot surface ignition of fuel sprays has been implemented in some practical situations, but the complex nature of flame formation within the spray structure poses s...
Article
A review of fundamental research in combustion stabilization for hypersonic airbreathing propulsion is presented. Combustion in high-speed airbreathing propulsion systems demands stable flame distribution and chemical reaction to provide reliable thrust over a wide flight envelope. Various methods have been developed to stabilize combustion dependi...
Conference Paper
Ignition characteristics of F-24 jet fuel injected into a combustion chamber with a hot surface probe were studied for reliable combustion of aviation compression ignition engines. The effects of the fuel injection pressure, hot surface temperature, and the location of the hot surface tip on ignition behavior at the aircraft operating conditions we...
Article
Full-text available
A robust tunable diode laser absorption spectroscopy (TDLAS) based system is developed and deployed to make real-time water-vapor concentration measurements in quasi-controlled live-fire experiments conducted in firefighter training props. This system targets the 1392.5 nm (7181.15 cm⁻¹) water-vapor absorption line while employing a multi-tier dete...
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Full-text available
A new direct-connect supersonic combustor has been designed and tested for the study of plasma-assisted combustion in the ACT-II supersonic combustion tunnel. Laser-induced plasma ignition was investigated in an ethylene-fueled cavity flame holder at Mach 3. Combustor design, geometry, and flow characteristics are discussed in the first part of the...
Article
A diffusion mesoscale burner array with integrated fuel manifold and injection holes has been developed for compact and efficient propulsion and power systems. Each burner element is equipped with its own fuel injection holes built into its swirl-inducing geometry to improve flame interaction and reduce flame length. The diffusion mesoscale burner...
Article
Individual flames in a swirl-stabilized mesoscale burner array can interact with neighboring flames for optimum burner array operation, particularly at lean equivalence ratios. Understanding these interactions are therefore critical for optimizing the mesoscale burner array. This study probes the effect of burner performance and stability based on...
Article
Full-text available
Incipient choking and unstart initiation mechanisms are investigated experimentally in an ethylene-fueled constant-area direct-connect supersonic combustor with a circular cross section (diameter of 28 mm) and full optical access. The experiments are performed in the ACT-II pulsed arc-heated hypersonic wind tunnel of the University of Illinois at U...
Article
Full-text available
Dual-mode operation and mode transition are experimentally investigated in optical axisymmetric scramjets in Mach 4.5 flows. The axisymmetric scramjet emphasizes generic combustion and flameholding dynamics without the corner boundary-layer effects that can distort flame propagation in rectangular geometries. Flow and combustion dynamics are charac...
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Full-text available
There are currently important questions in the fire service as to the efficacy of various fire attack methods, both in terms of rapidly suppressing the fire and for potentially impacting the burn risk for occupants in the structure. A series of 24 full-scale residential fire experiments were performed to investigate the influence of fire size and f...
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Full-text available
Cavity-enhanced combustion in an optical axisymmetric scramjet with a diverging combustor is experimentally investigated in Mach 4.5 flows. The axisymmetric scramjet emphasizes generic combustion and flameholding dynamics without the corner boundary-layer effects that can distort flame propagation in rectangular geometries. Combustion dynamics is c...
Article
The effects of inlet distortion and shockwave interaction on fuel-air distribution and ignition in a cavity-based flameholder with supersonic flow were investigated using nanosecond-gated laser-induced breakdown spectroscopy (n-LIBS). Experiments were conducted in a Mach-3 freestream direct-connect-type wind tunnel with direct cavity fueling. Ethyl...
Conference Paper
Full-text available
A study of cavity-enhanced combustion for a scramjet in Mach 4.5 high-enthalpy flow was conducted. In order to investigate the combustion and flameholding physics without corner boundary-layer effects present in rectangular geometries, an axisymmetric model was developed. The modular scramjet design allowed for parallel testing of both a cavity and...
Article
Full-text available
Combustion characteristics of a mesoscale burner array have been studied using several diagnostic and analysis techniques. The array was specifically configured to enhance overall combustion stability, particularly under lean operating conditions, by promoting flame to flame interactions between neighboring elements. The 4 × 4 burner array demonstr...
Article
The dynamics of an optical axisymmetric scramjet, preferred for generic combustion and flameholding studies without the corner boundary-layer effects that distort the freestream and flame propagation in rectangular scramjets, is investigated at Mach 4.5. Ethylene fuel is injected into supersonic flow via sixteen sonic fuel nozzles equally spaced in...
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Full-text available
Simultaneous particle image velocimetry (PIV) and planar laser-induced fluorescence (PLIF) utilizing R-branch transitions in the C-X (0,0) band were performed at a 10-kHz repetition-rate in a turbulent premixed flame. The CH lines at 310.690 nm (from the R-branch of the C-X band) used here have greater efficiency than A-X and B-X transitions, which...
Article
Full-text available
Combustion stability is an important consideration for many energy systems due to its impact on performance and efficiency. Flame dynamics that govern combustion stability are often complex and difficult to resolve, particularly from experimental data. However, recent advances in post-processing techniques, such as dynamic mode decomposition (DMD),...
Article
The reactivity of six kerosene based control fuels, specifically formulated for cetane number variation, are investigated by measuring ignition delay time in a heated rapid compression machine. Cetane numbers vary from 30 to 55 (increment of 5) while holding other properties relatively constant by adjusting chemical group composition. Main cetane v...
Article
Planar laser-induced fluorescence (PLIF) of hydroxyl (OH) and formaldehyde (CH2O) radicals was performed alongside stereo particle image velocimetry (PIV) at a 20 kHz repetition rate in a highly turbulent Bunsen flame. A dual-pulse burst-mode laser generated envelopes of 532 nm pulse pairs for PIV as well as a pair of 355 nm pulses, the first of wh...
Article
This communication describes and demonstrates an approach to making simultaneous multi-scalar measurements with reduced equipment requirements. Specifically, this letter describes and demonstrates the ability to simultaneously acquire high-quality planar laser-induced fluorescence (PLIF) images of CH2O and either CH, OH, or a combination of CH and...
Article
Planar laser-induced fluorescence (PLIF) of hydroxyl (OH) and formaldehyde (CH2O) radicals was performed alongside stereo particle image velocimetry (PIV) at a 20 kHz repetition rate in a highly turbulent Bunsen flame. A dual-pulse burst-mode laser generated envelopes of 532 nm pulse pairs for PIV as well as a pair of 355 nm pulses, the first of wh...