About

Christopher Cadou is a Professor in the Department of Aerospace Engineering at the University of Maryland, where he also serves as the Director of Undergraduate Studies and is affiliated with the Maryland Energy Innovation Institute. He holds a B.S. and B.A. from Cornell University, an M.S. and Ph.D. from the University of California, Los Angeles, and has conducted extensive interdisciplinary research in combustion, micro-fluidics, small power systems, and fuel cells. His research involves both micro and conventional scales of combustion, laser diagnostics, compact power systems, and energy-related technologies. Cadou's professional background includes positions as an Associate Professor at the University of Maryland since 2006, where he has been engaged in developing innovative combustion and micro-engine technologies. His prior experience includes postdoctoral work at the Massachusetts Institute of Technology, focusing on micro-gas turbines and hydrocarbon combustors, and at Caltech, investigating shock wave-boundary layer interactions in SCRAMJet inlets. His early research at UCLA involved laser diagnostics of reactive flows and waste incineration, while his undergraduate work at Cornell involved infrared absorption spectrum analysis of gas mixtures. He is actively involved in the professional community, serving as a reviewer for numerous scholarly journals and funding agencies, and participating in technical committees and conferences related to propulsion, combustion, and micro-engineering.

Research topics

• Optics
• Mechanics
• Physics
• Engineering
• Aerospace engineering
• Electrical engineering
• Automotive engineering
• Mechanical engineering

Selected publications

• Cycle Analysis of Gas Turbine / Solid Oxide Fuel Cell Hybrids for Aircraft

  2026-01-08

  articleSenior author

  Turbine-fuel cell hybrids offer the potential to reduce fuel burn over direct turbogenerators in all-electric aircraft. However, understanding how to configure them optimally for a particular vehicle and mission is difficult because the need to represent both the gas turbine and fuel cell accurately results in models that are complex and slow. It also makes it hard to develop an understanding of the basic trades that drive design generally. This paper presents a simplified analytical model of the hybrid thermodynamic cycle that is computationally efficient and thus suitable for performing design trade studies in aircraft. It is demonstrated on a B737 class aircraft where it is used to assess the effects of design choices like cycle pressure ratio and the turbogenerator/fuel cell power split on basic vehicle performance parameters like range and fuel burn. Key findings are that the hybrid system can reduce fuel burn by ~20% and that the 'breakeven' performance of the reformer/fuel cell element (the performance needed to realize the reduction in fuel burn with no reduction in payload or range) is ~1kW/kg. Further improvement in reformer/fuel cell specific power will increase payload and range relative to the baseline vehicle.

  PublisherDOI

• Development of a Pressurized Solid Oxide Fuel Cell Testing Facility

  2026-01-08

  articleSenior author

  This paper describes the development and validation of a facility for measuring fuel cell performance at pressure. Such data are needed to design the turbine-fuel cell hybrid energy conversion systems envisioned for ultra-efficient aircraft. The facility consists of a pressure vessel with water-cooled walls, heaters, temperature and pressure controls, a gas management system, a humidification system, and a programmable electrical load. Polarization curves of a commercial YSZ-based fuel cell measured in the facility are found to be consistent with theory and the manufacturer's specifications at 1 bara. Increasing the pressure to 4 bara increases peak power density by about 10% in this particular cell. Other scientifically interesting phenomena can also be observed like the drop in cathode pressure associated with increased current density and oxygen transport. Future experiments will use the facility to measure pressure effects in other types of cells and short fuel cell stacks.

  PublisherDOI

• Hybrid SOFC-Turbogenerator for Aircraft (Final Scientific/Technical Report)

  2025-10-31

  reportOpen access1st authorCorresponding
  PublisherOA PDFDOI

• Evaluating Operating Conditions and Thermal Management in High Power Density Solid Oxide Fuel Cells

  ECS Meeting Abstracts · 2025-11-24

  article

  Solid oxide fuel cells (SOFCs) with their high energy conversion efficiencies offer a way to use dense hydrogen-rich liquid fuels for hybrid electric power in transportation applications. Doped ceria electrolytes have high ionic conductivity and can achieve area-specific power-densities above 1.0 W cm -2 at intermediate temperatures below 700 °C. This work reports a physics-based model to characterize the performance of a gadolinia-doped ceria (GDC) electrolyte-based SOFC at high power-density operating scenarios. The model couples defect thermochemistry, charge transfer kinetics for multiple reactions, and porous media transport in both electrodes to quantify how the mixed ionic-electronic conduction of GDC impacts cell performance. The model is experimentally validated with button cell data over a range of operating temperatures (500-650 °C) and pressures (1.0 - 5.0 bar). A down-the-channel version of the model for operation with both hydrogen and autothermally reformed methane gas shows that high power densities necessitate cathode flows with excess air ratios ≥ 5 to sustain axial temperature gradients ≤ 15 K cm -1 Simulations indicate no power density benefit of operating the GDC cell at temperatures above 680 °C due to the rapid increase in polaron leakage current through the electrolyte membrane at those temperatures. Polaron leakage can be mitigated by operating at cell voltages below 0.7 V, although continuous operation at high current densities associated with these voltages may induce shorter cell lifetime. Power densities over 1.0 W cm -2 can be achieved at the cell level for pressurized operation with careful control of operating temperature and excess air ratio. Such power densities can enable stack specific power of over 1 kW kg -1 that can accelerate the adaptation of SOFCs in the transportation sector. Introduction: Solid oxide fuel cells (SOFC) have the potential to convert low-carbon and alternative fuels to electric power at high conversion efficiencies to offset the lower energy density of many of these fuel sources. However, the low power-to-weight ratios and operating temperature of SOFCs limit their applicability for transportation applications such as aviation. Gadolinia-doped ceria (GDC) has an ionic conductivity over 0.01 S cm -1 at 550 °C [1] which can enable high SOFC power density (> 0.5 W cm -2 ) for intermediate temperature (500 – 700 °C) operation. From the perspective of application in the transportation sector, an electrolyte strategy that offers high power-density at intermediate temperature operation is particularly beneficial as it enables effective system integration. The requirement of heat exchangers for preheating the inlet gases can be minimized or eliminated as compressor exhausts can directly supply SOFC inlets which greatly reduces system complexity and improves power-to-weight ratios. This work presents a detailed computational model to investigate the performance of an SOFC based on GDC electrolyte for high power-density operation scenarios. The model is used to evaluate the effect of electronic leakage and characterize cell performance for operation with hydrogen. Methodology: Gadolinia-doped ceria (GDC) is a mixed ionic-electronic conductor. Under reducing conditions that are typical in the fuel electrode of an SOFC, the cerium ion can be reduced from a 4 + to 3 + oxidation state (polaron). In addition to oxygen vacancies, it can also conduct electrons through the polaron hopping mechanism, whereby the electronic conductivity is substantial at higher temperatures [2]. Along with the hydrogen oxidation reaction at the triple-phase boundaries, polaron formation occurs at the electrode-electrolyte interface and can be represented as: Ce +4 + e - ↔ Ce +3 This simultaneous conduction of vacancies and polarons manifests as a potential drop through the electrolyte membrane that reduces the open-circuit voltage relative to the theoretical Nernst-potential. The electrochemical model employed in this work considers the treatment of multiple charge carriers where the charge-balance accounts for hydrogen oxidation and polaron formation charge transfer rates. Charge flux due to diffusion and migration is represented in the Nernst-Planck formulation: J k = - D k ∇[ X k ] - z k FD k [ X k ]∇Φ el /( RT ) The charge-carrier conductivities are represented through the Nernst-Einstein formulation where the conductivity parameters have been calibrated in Zhu et al [2]. An isothermal button cell model of the Ni-GDC | GDC | SSC-GDC is used for calibration of experimental data at varying operating conditions. The 1D button cell model includes continuum-level description of the porous electrodes with the dusty-gas formulation for gas flux evaluation [3,4]. A quasi-2D down-the-channel model couples the electrochemical model with mass, momentum and energy balances in anode and cathode channel flows. The down-the-channel model is used to evaluate high power-density operation scenarios at relevant cell voltages and operating temperatures. Results: Figure 1 shows the parity plot of experimental vs. simulated cell voltage for validation of the button-cell experimental data. The model and experimental data are based on a GDC electrolyte based cell architecture. The plot shows excellent agreement with measured data on humidified hydrogen and air at 550, 600 and 650 °C and ambient pressure conditions. Extended Butler-Volmer kinetic equations that are derived assuming rate-limiting chemistry for elementary charge transfer mechanisms are used to describe charge transfer processes. The calibration parameters include symmetry factors, reference exchange current densities and activation energies. The model is simulated for pressurized operating conditions and is compared to experimental data [5] at 5 bar as proof of further validation. Figure 2 shows the simulation results when cell is simulated with a two-dimensional down-the channel model with mass, momentum, charge and energy balances. In this case, the fuel feed is humidified hydrogen (99% H 2 , 1% H 2 O) at the system inlet with 50% anode-gas recycle. Therefore, the fuel feed at the anode inlet is approximately 75% hydrogen and 25% steam. The air flow is varied such that the cell reaches the desired average cell temperature for inlet temperatures of 550°C. Figure 2a shows power-density for three different operating voltages as a function of average cell temperature. The results show that there is a non-monotonic trend for the predicted power-density as a function of the average cell temperature. When the local cell temperature increases over 700°C, the cell starts to produce an excess of polaron flux that manifests as electronic leakage and additional heat generation. As a result, local external current density at the end of the cell decreases which results in the decrease in overall power density. The temperature at which the maximum power-density is obtained depends on the operating voltage. For example, the maximum power-density arises at 630°C for cell operation at 0.75 V but arises at 645°C for operation at 0.70 V. Figure 2b shows the faradaic efficiency for the simulations. The faradaic efficiency quantifies the effectiveness of fuel conversion to electric current and is an important performance metric in mixed ionic-electronic conductive cells. In fuel cell mode, it is defined as the ratio of external current to the flux of hydrogen consumed in the anode [6]. The faradaic efficiency decreases at higher operating temperatures as more hydrogen is used to sustain the polaron flux due to the increasing polaron c

  PublisherDOI

• Developing Standard Operating Procedures for Solid Oxide Fuel Cell Testing at Elevated Pressures

  2025-01-01

  articleSenior author

  Turbine-fuel cell hybrids in which high temperature fuel solid oxide fuel cells (SOFCs) are placed within the hot section of the engine are being studied as compact and efficient sources of electric power for aircraft with distributed electric propulsion. However, there are few studies that consider the effect of pressurization on fuel cell performance making it hard to make accurate predictions of such system’s performance. One reason for this lack of data is that measuring SOFC performance at pressure is difficult: the cell must be tested in a pressurized furnace at temperatures up to 750C while remaining electrically isolated from its surroundings. This is made harder by the relatively large number of fluidic and electrical connections and components required to control temperature and pressure, deliver reactants to and from the cell in the correct proportions, collect the cell’s current, measure its voltage, and measure pressures, temperatures, and mass flow rates in various other places in the system. This paper describes the development of a set of standard operating procedures for the University of Maryland’s pressurized SOFC testing facility. Such procedures are essential for ensuring that the facility operates safely while producing reliable data. The current version of the SOP in use highlights the additional complexities that come with testing SOFCs at elevated pressures. The use of a pressure vessel inherently limits access to the cell, sensors, and balance of plant equipment. As such, the SOP contains continuity and leak checks at multiple stages of the build-up and sealing process to ensure problems can be resolved with as few obstructions as possible, saving time and potentially materials in the process. Assuming the sealing process is completed with no issues, pressurized testing increases the potential for leaks outside the pressure vessel, while the varying pressure conditions inside can lead to transient pressure differences between anode, cathode, and bath flows. Therefore, it is important to include more precautions to reduce the likelihood of gas leaks than for atmospheric fuel cell testing, and set procedures for changing the pressure setting must be established to avoid damage to the SOFC under test.

  PublisherDOI

• Integrated Autothermal Reformer, Heat Exchanger and Solid Oxide Fuel Cell in Single-Stack for Aircraft Gas-Turbine Applications

  ECS Meeting Abstracts · 2024-11-22

  article

  To take advantage of carbon-neutral aviation fuels such as synthetic liquified natural gas, aircraft engines must increase their efficiency through novel approaches, such as hybrid electric gas-turbine/solid oxide fuel cells (GT/SOFCs). To date, most hydrocarbon-fueled SOFC stack designs utilize rigid architectures and independent pre-reformers that require complex manifolding and rigid sealing. To enable SOFCs to operate effectively and robustly within an aircraft GT engine flow path upstream of a combustor, our team is developing an innovative integrated SOFC stack with an inline autothermal reformer/heat exchanger (ATR/HX) to provide adequate operating conditions for high-power (W/cm 2 ) performance. The ATR/HX, integrated upstream of the stack, provides preheating of the cathode air through mildly exothermic reforming of the fuel with a bleed of combustor air and recycling of some anode exhaust. The exothermic ATR provides adequate heat to the cathode air to allow intermediate-temperature SOFCs, with either gadolinium-doped ceria (GDC) electrolytes or thin-film yttria-stabilized zirconia (YSZ) electrolytes, to operate on GT compressor outlet temperatures just above 400 °C. To enable rapid thermal response of the integrated ATR/HX/SOFC, the stack design eliminates rigid seals to mitigate the risks of SOFC failure due to thermomechanical stresses. This paper presents the design and preliminary testing of the integrated ATR/HX/SOFC under rapid heating conditions to suggest the potential for SOFCs for next generation hybrid-electric aircraft application. The ATR/HX/SOFC stack design is supported by 441 stainless steel plates with electrochemically etched, air-flow channels through the upstream HX and the SOFC cathode. The plates also include a pocket for the ATR, which consists of a woven metal-mesh with an Al 2 O 3 -washcoat supported Pt catalyst that can light off with CH 4 /bleed air/H 2 O inlet temperatures of 400 °C. The SOFC membrane electrode assembly (MEA), 10 cm*10 cm with 81 cm 2 active cathode area, rest within a frame that supports the MEA as well as a silver mesh cathode collector and a nickel mesh anode current collector. The cell is sealed by compressing a thermiculite seal that extends over the full area of the stack and compresses on the exposed electrolyte area bordering the cathode. Testing at operating temperatures indicated minimal leakage (<1%) from the anode and from the cathode to the external environment. This design, which lacks rigid seals or confinement of the MEA, enables ease of assembly and disassembly and minimizes external stresses on the MEA to enable rapid heating during ATR light-off. Integrated ATR/HX/SOFC stack has been initially incorporated into a low-pressure test facility shown in Figure 1a), which provides steam generation for the ATR inlet and premixing and preheating for the ATR inlet and air-side HX inlet flows. The ATR/HX/SOFC stack is preheated to 400 °C or more to achieve rapid light-off that rapidly preheats the SOFC inlet to desirable temperatures. For a 3-cell ATR/HX/SOFC short stack, light-off test to SOFC operating temperatures of 550 °C for thin-film YSZ-electrolyte MEAs from Elcogen are achieved in < 1 h. Such start-up times are expected to be reduced for larger ATR/HX/SOFC stacks with reduced heat loss per stack volume. Tests to date have only achieved maximum MEA power densities of 0.26 W/cm 2 at 0.65 V/cell operating on the ATR outlet. Simulated performance shows pathway to higher power densities > 1.0 W/cm 2 with higher temperature operation that will be achieved with coated interconnect materials. Tests to date show that the thin-film YSZ cells avoid cracking after undergoing multiple assembly and disassembly cycles, as well as high-temperature ATR light-off and fuel cell testing. These results indicate that both mechanical and thermal stresses remain sufficiently low to prevent cell cracking throughout start-up, normal operation, and shut-down processes, thus affirming the robustness and reliability of our integrated stack design. Figure 1

  PublisherDOI

• Possible Effects of Turbine/Fuel Cell Integration on Combustor Operation Part II: Ignition Delay and Flame Temperatures

  AIAA SCITECH 2023 Forum · 2023-01-19

  articleSenior author

  View Video Presentation: https://doi.org/10.2514/6.2023-1462.vid Previous work has shown that replacing shaft-driven mechanical generators with more efficient high temperature fuel cells integrated directly into the hot section of a turbine engine can significantly extend the range and endurance of uncrewed aerial vehicles and civil transport aircraft with large electrical loads. One advantage of this hybridization is that fuel not consumed in the fuel cell is burned in the combustor to produce propulsive power enabling the use of smaller/lighter fuel cells. However, the impacts of introducing this hydrogen-containing and thus highly reactive secondary fuel stream into the combustor are unknown. An initial paper showed that the residual heating value in the fuel cell exhaust is significant accounting for 20% of the overall heat release when 30% of the total system power was provided by the fuel cell. It also showed that the composition of the fuel cell exhaust was most influenced by the utilization. This follow-on paper investigates the impacts of fuel cell exhaust on the fundamental parameters of flame temperature and ignition delay time in the combustor due to varying SOFC fuel utilization and SOFC electric power fractions. The results show that ignition is enhanced by up to two orders of magnitude when the fuel cell operates at higher fuel utilizations due to the higher initial temperatures of the exhaust mixtures, even while the adiabatic flame temperature is reduced. The relatively large changes in the magnitudes of these fundamental combustion characteristics suggest that a) combustors in turbine/fuel cell hybrids may need to be designed differently to accomodate these variations and b) that introducing fuel cell exhaust could be used to reduce NOx emissions by enabling stable combustor operation at lower overall equivalence ratios.

  PublisherDOI

• Non-Intrusive Velocimetry in a Supersonic Reacting Flow using Two-Point Focused Laser Differential Interferometry

  AIAA SCITECH 2023 Forum · 2023-01-19 · 4 citations

  articleSenior author

  View Video Presentation: https://doi.org/10.2514/6.2023-0223.vid Two-point focused laser differential interferometry (2pFLDI) is shown to be a viable technique for making non-intrusive measurements of velocity in supersonic reacting flows. Velocity is computed from the cross-correlation of two FLDI signals from two closely-spaced (∼ 168micron in the streamwise direction) measurement volumes. The technique is demonstrated in a 12.7mm-wide dual-mode scramjet combustor with Mach 2 vitiated-air inflow and T_0 = 1300K. Measurements are made at 10 locations along the combustor’s axis for two fuel injection schemes: (1) injection from a single port, and (2) injection from four axially-distributed ports. Measured axial velocity profiles confirm the existence of two distinct operating modes and are qualitatively consistent with velocities deduced by other means (a combination of pressure measurements, chemi-luminescence, and quasi 1-D compressible flow analysis) but are biased low. This bias is partially explained by the large size of the 2pFLDI’s sensitive region which extends beyond the width of the channel (for disturbances with wavenumbers, k_x, less than 12.4mm^−1 ) thereby enabling lower momentum fluid in the boundary layers on the facility’s windows to influence the signal. A cross-spectral analysis of the FLDI signals enables one to calculate velocity as a function of disturbance scale which is important because the instrument’s resolution and sensitivity are functions of disturbance scale. Velocities for k_x > 13mm^−1 are in better agreement with the deduced velocity because the FLDI is sensitive to these disturbances with resolution which is smaller than the width of the channel and closer to the techniques used for the deduced velocity.

  PublisherDOI

• Interaction Behavior of Pulsejet Engines

  Journal of Propulsion and Power · 2023-02-01 · 3 citations

  articleSenior author

  Valveless pulsejet engines are analyzed as electric circuits in which the main engine components (inlet, combustion chamber, and tailpipe) are assigned impedance values and represented using a system of linear equations. The solution to these equations yields Bode plots for the engines that can be used to predict operating frequency as well as the effects of individual component dimensions on overall engine behavior. This method of analysis is found to predict engine operating frequencies to within 7% of experimentally measured values. The analysis is extended to include systems of multiple engines and again verified by comparison to experiment. It is shown that multiple engines can be locked in phase or in antiphase predictably by selecting the proper interconnection method. The latter has important implications for noise reduction and for propulsion applications involving arrays of pulsejets.

  PublisherDOI

• Interpreting single-point and two-point focused laser differential interferometry in a turbulent jet

  Experiments in Fluids · 2022 · 23 citations

  Senior authorCorresponding
  • Physics
  • Optics
  • Mechanics
  PublisherDOI

Frequent coauthors

• Ananthanarayanan Veeraragavan

  University of Queensland

  19 shared

• Kiran Dellimore

  15 shared

• Timothy Leach

  CFD Research Corporation (United States)

  10 shared

• André Marshall

  9 shared

• Daanish Maqbool

  University of Maryland, College Park

  8 shared

• Daniel F. Waters

  University of Maryland, College Park

  8 shared

• Andrew Ceruzzi

  7 shared

• Shyam Menon

  5 shared

Awards & honors

• NSF Graduate Research Fellowship Program (2023)
• Seven undergraduate aerospace engineering students recognize…
• 2022 Wings Club Scholarship