About

Professor Tonghun Lee is a faculty member in the Department of Aeronautics and Astronautics at Stanford University. His research group investigates the fundamental physics relevant to next-generation aerospace propulsion systems and space entry technologies. His areas of interest include hypersonic propulsion systems, hybrid chemical and electrical propulsion systems, compact UAV propulsion technologies, the integration of sustainable aviation fuels, and the application of advanced laser and optical diagnostics. His work aims to enhance the fundamental understanding of high-speed reacting flows and to advance technologies for more efficient and environmentally responsible aerospace systems. Professor Lee has received numerous honors and awards, including the Best Technical Paper and Walter Lempert Best Paper Award at AIAA SciTech 2021, and has been recognized as an Associate Fellow of AIAA and a Fellow of the American Society of Mechanical Engineers. His educational background includes a Ph.D. and M.S. in Mechanical Engineering from Stanford University and a B.S. from Yonsei University. He is actively involved in research and contributes to the advancement of aerospace propulsion technologies through his leadership and scientific contributions.

Research topics

• Computer Science
• Physics
• Mechanics
• Materials science
• Chemistry
• Structural engineering
• Engineering
• Composite material
• Medical emergency
• Medicine
• Emergency medicine
• Thermodynamics
• Aerospace engineering
• Mechanical engineering
• Anesthesia
• Organic chemistry
• Simulation

Selected publications

• Numerical Simulation of Scram-Mode Operation of an Axisymmetric Combustor in an Arc Tunnel

  Journal of Propulsion and Power · 2025-03-11 · 4 citations

  article

  Large-eddy simulations of scram-mode operation of an axisymmetric inlet–isolator–combustor configuration experimentally tested in the ACT-II arc-heated combustion tunnel are presented in this work. A 32-species ethylene oxidation mechanism including nitric oxide decomposition reactions is used for most calculations; sensitivities due to the use of a 43-species model are also assessed. Numerical flame stabilization under conditions of the experiment (Mach 4.5 inflow, equivalence ratio of 0.82) is a sensitive function of the rate of energy release within the combustor. This can be altered by changes in the inflow oxygen atom composition (using values obtained from simulations of the arc heater itself) and the choice of reaction mechanism, but even with these controls, it was found necessary to threshold the pressure level supplied to the reaction rates to achieve stable supersonic combustion within the unit. The results presented show a strong sensitivity to these controlling factors in that good agreement with experimental trends can be obtained for specific combinations, but the prescription is not unique. The predictions show that scram-mode operation occurs under lean premixed conditions, characterized by a predominance of CO, little formation of [Formula: see text], an appreciable temperature rise, and an OH signal that rises substantially before increases in the formation rates of the major combustion products.

  PublisherDOI

• Optical Diagnostics of Cavity-Stabilized Combustion in an Axisymmetric Dual-Mode Supersonic Combustion Flowpath

  2025-01-03

  articleSenior author

  Cavity-stabilized combustion is performed in a generic axisymmetric dual-mode reactive flowpath with varying fueling locations and equivalence ratios at a total enthalpy matching that of Mach 7 flight. Quantitative pressure measurements are performed simultaneously with qualitative broadband and OH-PLIF optical diagnostics. For low equivalence ratios or pre-isolator fueling, autoignition is not observed within this flowpath. Higher equivalence ratios (ϕ = 0.75 and ϕ = 1) at pre-cavity fueling locations exhibit cavity-stabilized combustion but produce two visually different modes within the diverging-area combustor region of the engine. Pressure traces in the same region do not show any significant difference. For initially non-lighting conditions, a modified aerothrottling scheme is utilized to encourage ignition, then disabled for the remainder of the run before steady-state measurements are taken. A high-pressure plume of ethylene is injected downstream of the cavity flameholder to increase backpressure and temporarily provide conditions favorable for ignition. With this scheme, most unassisted non-lighting cases are capable of igniting and remaining stable for the remainder of the run, even once the aerothrottle injection is disabled.

  PublisherDOI

• Influence of operating conditions on the degradation of co-annular Si₃N₄-MoSi₂ glow plugs

  Journal of the European Ceramic Society · 2025-10-25

  articleOpen access

  Silicon-nitride-based composites are widely used in ceramic heaters for combustion engines due to their high strength and wear resistance. Recent developments in engine designs, focusing on using alternative jet fuels with lower auto-ignition tendencies, have increased the demand for ignition-assistance devices. However, extended operation of glow plugs at high temperatures, beyond their intended use, accelerates degradation processes, thereby reducing durability. To design improved materials for this application, investigating the degradation modes of state-of-the-art glow plugs is crucial. This paper presents experimental results on co-annular glow plugs tested in three operating environments: ambient air, constant airflow chambers, and combustion engines. XRD, SEM microscopy, and Micro-CT were used to characterize microstructural changes alongside resistance behavior. Observed degradation modes in co-annular designs included surface oxidation, volatilization, sintering aid migration, and internal cracks caused by thermal stress from CTE mismatch. The primary degradation mode of this glow plug design was surface oxidation, as the resistive heating occurred at the outermost surface, making it particularly susceptible to surface degradation.

  PublisherDOI

• Numerical and experimental analysis of a dual-channel electric motor housing cooling system

  Applied Thermal Engineering · 2025-01-16 · 6 citations

  article
  PublisherDOI

• Local hotspot characterization of an electric vehicle battery module using optical fiber thermometry

  Measurement · 2025-11-16

  article
  PublisherDOI

• In-situ tailpipe soot emission monitoring for diesel engine exhaust using a quartz-enhanced photoacoustic spectroscopy sensor

  Measurement · 2025-01-07 · 3 citations

  article
  PublisherDOI

• Capture-Independent Leading-Edge Reshaping Via Profile-Truncated Streamline Tracing

  SSRN Electronic Journal · 2025-01-01

  preprintOpen accessSenior author
  PublisherDOI

• Numerical and Experimental Investigation of a Mach 7 Reactive Flowpath

  2025-01-03 · 1 citations

  articleSenior author

  High-fidelity simulation of a round supersonic reactive flowpath are presented. The geometry and conditions were designed to enable a combined research effort between experimentation and computation of a high-speed reacting flowfield representative of Mach 7 flight in order to study the fundamental physical phenomena occurring between the turbu�lence and chemical reactions. An initial comparison between preliminary experimental runs and high-resolution simulation data is made. A qualitative investigation of the simulation data reveals several key features of the resulting flowfield including combustor pressure distribution, Mach number distribution, flame structure and heat release rates. Analysis of the flame index in the simulations shows that both premixed and diffusion flames occur at the current conditions. An enstrophy budget analysis indicates that both dilatation and baroclinic mechanisms are significant in this flow.

  PublisherDOI

• Capture-independent leading-edge reshaping via profile-truncated streamline tracing

  Aerospace Science and Technology · 2025-10-27

  articleSenior authorCorresponding
  PublisherDOI

• Development of an Optically Accessible Mach 3.5 Axisymmetric Direct Connect/Semi-Free Jet Supersonic Combustion Flowpath

  2025-01-03

  articleSenior author

  An axisymmetric Mach 3.5 direct connect supersonic combustion flowpath has been developed at the University of Illinois Urbana-Champaign for use in fundamental studies on high-speed combustion stabilization, scram and ram combustion performance, and mode transition. The current work outlines the first two iterations of the flowpath design, along with accompanying validation and preliminary measurements conducted in the Arc-Heated Combustion Tunnel (ACT-II) at Mach 7 total enthalpy conditions with ethylene fueling. These measurements include static pressure measurements on the flowpath wall, pitot measurements at the combustor exit, and optical measurements including OH* and broadband chemiluminescence, isolator plasma luminescence, and OH PLIF of the combustor flowfield. To enhance the diagnostic potential of the flowpath, optical access is featured along 80% of the flowpath length. The earliest prototype of the flowpath exhibited poor combustion and flameholding characteristics, and an inability to engage mode transition. The fault was assessed to be the rapid geometric expansion at the flameholding station of the combustor and an attendant reduction in static pressure, resulting in adverse ignition performance and shortened combustor residence time. Based on these initial results, the flowpath was redesigned with a longer combustor, a deeper flameholding cavity with a 30° takeback ramp, and an additional stage of fuel injection. Early tests of this second flowpath show promising results for both ignition and flameholding performance and demonstrate the capability for mode transition. Pulsed injection-induced ignition was also successfully tested in this new geometry. A semi-free jet flowpath was developed based on the revised direct connect model. Mach 4.5 high enthalpy free jet tests of this new geometry were conducted in the ACT-II. The results confirm full flowpath startability and inlet performance of the unfueled semi-free jet flowpath model.

  PublisherDOI

Frequent coauthors

• Stephen D. Hammack

  37 shared

• Campbell D. Carter

  United States Air Force Research Laboratory

  34 shared

• Eric Mayhew

  United States Army Combat Capabilities Development Command

  28 shared

• Jihyung Yoo

  Hanyang University

  26 shared

• Chol-Bum Kweon

  United States Army Combat Capabilities Development Command

  23 shared

• Rajavasanth Rajasegar

  Sandia National Laboratories California

  21 shared

• Jacob Temme

  21 shared

• Anna Oldani

  Federal Aviation Administration

  17 shared

Education

• Ph.D., Aeronautics and Astronautics

  Stanford University

  2000

• M.S., Aeronautics and Astronautics

  Stanford University

  1996

• B.S., Mechanical Engineering

  University of California, San Diego

  1994

Awards & honors

• Best Technical Paper, High Speed Airbreathing Propulsion TC,…
• Walter Lempert Best Paper Award, AIAA SciTech 2021 (2021)
• Associate Fellow, AIAA (2020)
• Fellow, American Society of Mechanical Engineers (2020)
• Visiting Scientist Award, Argonne National Laboratory Advanc…