The HyFLAME Lab

The HyFLAME Lab at the University of Ottawa is dedicated to advancing the fundamental science of high-speed reactive flows. We investigate the complex physics of spontaneous ignition, flame acceleration, and the transition to detonation in low-carbon fuels—specifically hydrogen and natural gas. Our goal is to bridge the gap between theoretical fluid mechanics and the practical engineering required for a zero-emission energy future.

Core Research & Impact

Our work addresses two of the most critical challenges in the modern energy landscape:

Clean Energy & Power: Developing next-generation power cycles that maximize the potential of carbon-free fuels.
Safety & Risk Mitigation: Quantifying and reducing explosion hazards inherent in the storage and transportation of high-pressure hydrogen and gas mixtures.

Computational Excellence

At the heart of our laboratory is the development and application of advanced Computational Fluid Dynamics (CFD) strategies. We specialize in pushing the boundaries of high-speed combustion, modeling environments characterized by:

Extreme Mach Numbers: Supersonic and hypersonic flow regimes.
High Reynolds Numbers: Resolving the intricate scales of intense turbulence.
Turbulent Combustion: Developing and implementing high-fidelity models to solve the complex coupling between turbulent fluid motion and rapid chemical heat release.

Our Team

Brian Maxwell, Ph.D., P.Eng.

Associate Professor, Department of Mechanical Engineering, University of Ottawa

Brian Maxwell CFD | Director of the HyFLAME Lab.

Email: bmaxwell@uottawa.ca

Check out Professor Maxwell’s publications on his Google Scholar and Researchgate pages. Also be sure to check out videos of his work on YouTube!

Our Research

Detonation Fundamentals

The study of detonation waves has been ongoing for over a century, however industrial explosions still pose a significant risk, and cause billions of dollars of damage to the global economy every few years. This highlights difficulties in accident prediction, prevention, and mitigation. While it's known that a slow moving flame (deflagration) can develop into an explosion, or detonation, during an incident, its prediction remains extremely challenging. A significant thrust of our research is to better understand the detonation phenomenon, using the latest CFD tools and models available.

Combustion Model Reduction

Modeling of the chemistry and thermodynamics is a crucial component in numerical simulations that attempt to accurately simulate reactive flow dynamics. Our group has recently improved a global 4-species, 4-step premixed combustion mechanism that captures detailed chemistry reaction behavior and properties for a wide range of initial densities and temperatures. We also expanded this model to encompass a range of hydrocarbon fuels, beyond its original implementation for stochiometric acetylene-oxygen. The current model only requires 3 transport equations, which has a significantly lower memory overhead compared to detailed chemistry mechanisms. It also provides a much better description of the combustion stiffness and response to conditions compared to simplified one, two, and three-step models.

Hydrogen Research

With the emergence of new hydrogen technologies, there has been much focus on advancing research to understand ignition behavior of hydrogen leaks in order to assess explosion and safety hazards. A number of experiments have shown, to date, that hydrogen jets are easily ignitable, and have a wide range of ignition limits (between 4% to 75% by volume). It is therefore of paramount interest to understand the dispersive nature of hydrogen, a highly compressible gas, in order to adequately develop codes and standards. Our group has used three-dimensional large eddy simulation to model the dispersion of compressible hydrogen leaks, from a realistic piping configuration, in order to determine the extent of ignition limits associated with the respective release conditions considered.

Rotating Detonation Engines

The RDE is a unique type of pressure-gain combustion engine in which a highly reactive wave, the detonation, continuously propagates against the reactive mixture within a combustion chamber. Typical axially-oriented RDEs supply air to an annulus, while the detonation wave continuously propagates in the azimuthal direction. Higher efficiencies can be potentially realized compared to cycles relying on heat addition through constant pressure deflagrations such as the well-known Brayton cycle. Moreover, the conceptually simple geometry and configuration allows for compact devices to be constructed, leading to a wide range of scales at which RDEs can be designed for. The detonation wave is a key feature of RDEs, which not only provides compression of the reactive fuel-air mixture through incident shock compression, but also provides additional compression through a rapid and nearly constant volume combustion process. This results in elevated temperatures and pressures at the combustor outlet, which may permit increased thrust or mechanical work extraction compared to deflagration-based cycles. The detonation thermodynamic cycle has the potential increase of available compression ratios by about an order of magnitude compared to the deflagration-based Brayton cycle. In the video featured, a model natural-gas powered RDE has been simulated in an unwrapped configuration.

Pulse Detonation Systems

Our work is also focussed on advancing fundamental understanding of pulse detonation systems. Like the RDE, a detonation wave may be pulsed inside a tube to deliver thrust, potentially much more efficiently compared to the conventional Brayton cycle. Also, pulse detonation systems may be used for additive manufacturing, to deliver protective coatings to a manufactured part. Such methods are known to provide the densest and strongest protective coatings.

Turbulent Mixing Layers

Turbulence is everywhere. Some of our work has focused on exploring the nature of turbulence in high speed flows. The following link is a simulation of a supersonic shear layer. We do these types of simulations to validate our work.

Supernovae

In a type Ia supernova (SN1A), which occurs in a binary star system, a white dwarf (WD) consisting of mostly carbon-oxygen nearing its life cycle becomes so dense that it accrues stellar matter from a nearby companion star. This causes the WD's core to exceed the fusion temperature of carbon, triggering an intensely luminous thermal runaway nuclear fusion reaction that unbinds the star, ejecting stellar matter and the companion star into space. The brightness of an SN1A, now referred to as a universal standard candle, make it particularly interesting to study. It permits us to measure cosmological distances and study expansion of the universe. This consequently permits us to better understand the origins of our universe. Our work aims to investigate and model the nuclear physics involved in the potential unconfined deflagration to detonation transition (DDT) as a progenitor for the SN1A phenomena. This mechanism is also referred to as the Delayed Detonation Model. We are attempting to isolate and advance a fundamental understanding of the roles of turbulence in promoting the DDT process, and attempting to confirm whether or not DDT is a possible or likely mechanism to explain such types of stellar events.

CFD Capabilities

Our main in-house CFD codes are based on the MG platform (courtesy S. Falle at the University of Leeds), written in C. We use a variety of Godunov-type compressible flow solvers (Exact, Roe, HLLC). The MG platform is equipped with distributed memory parallelization capability and adaptive mesh refinement (AMR) for increased efficiency. This reduces computational overhead significantly by computing high resolution solutions only in regions of interest, see Fig. 1. Our CFD codes, including those fully developed in-house, are capable of using detailed combustion mechanisms or reduced mechanisms. Our codes are also equipped with the Compressible Linear Eddy Model for Large Eddy Simulation (CLEM-LES) turbulent combustion model, originally developed to model detonation waves. This approach is a grid-within-a-grid approach, as illustrated in Fig. 2, that resolves mixing and reaction on the subgrid scales, while providing significant savings compared to direct numerical simulation (DNS) of the governing Navier-Stokes equations. The advantage of CLEM-LES is its ability to handle a wide range of combustion regimes. High fidelity detail of the reaction zone structures are preserved on one-dimensional subgrid domains, which are supplemented by re-mapping procedures, or `stirring events', to account for the effect of turbulence on the subgrid. Application of the CLEM-LES to capture experimental observations of detonation waves is demonstrated in Fig. 3.

Figure 1: Example AMR grid topology (right) and corresponding temperature field (left) for a detonation wave in methane--oxygen at 4.5 kPa. The x and y scales go from 0 to 10 units and 615 to 635 units, respectively.

Figure 2: Computational cells required for DNS (left) compared to CLEM-LES (right). The coupling of energy between subgrid scale grids and large scale grids is through pressure changes, obtained on the large scales, and energy released due to combustion, obtained on the subgrid.

Figure 3: Comparison of experimental and simulated (CLEM-LES) detonation structures using a) and b) soot-foils, and c) and d) Schlieren (exp) and density (sim) flow fields. The scale on the left images indicates 10cm, and the scale in the right images indicates 20cm. The right images (c and d) indicate multiple cells on the detonation front, pockets of dense unburned gas, shockwaves, and turbulent flame surfaces.

Publications

For a full list of Professor Maxwell’s publications, please see his Google Scholar and Researchgate pages.

Simulation videos and online presentations of Professor Maxwell’s work can be found on YouTube.

Open Source Software

4-step combustion model for premixed hydrocarbon mixtures

The 4step-reactor code is a C++ reactor code for simulating constant volume, constant pressure, or ZND simulations using a simplistic and efficient global combustion model that mimics the ignition behaviour of premixed hydrocarbon combustion. The model is efficient because it only considers 4 reaction steps (induction with 2 pathways, reaction steps, and equilibrium of products), while only considering the evolution of as little as 3 species. The current version of this model is described in Ref [1], but was originally motivated by the formulation of Ref [2]. The model works for stoichiometric and lean mixtures. It does not yet work for rich mixtures. Work is ongoing to include mixtures involving hydrogen. Recent implementations have been published in Refs [3] and [4].

This code was written by Mohnish Peswani (Case Western Reserve University) and Brian Maxwell (University of Ottawa). Contact us if you are interested in using our code, or interested in collaborating on scientific or applied research.

Peswani, M., Gerace, C. & Maxwell, B. Combustion properties of a simple and efficient four-step model. Shock Waves 32, 517–537 (2022). https://doi.org/10.1007/s00193-022-01090-6
Zhu, Y., Yang, J. & Sun, M. A thermochemically derived global reaction mechanism for detonation application. Shock Waves 22, 363–379 (2012). https://doi.org/10.1007/s00193-012-0375-x
Floring, G., Peswani, M. & Maxwell, B. On the role of transverse detonation waves in the re-establishment of attenuated detonations in methane–oxygen. Combustion and Flame 247, 112497 (2023). https://doi.org/10.1016/j.combustflame.2022.112497
Peswani, M. & Maxwell, B. Detonation wave diffraction in stoichiometric C2H4/O2 mixtures using a global four-step combustion model. Physics of Fluids 34, 106104 (2022). https://doi.org/10.1063/5.0116804

Figure 4: Comparison of ignition delay times in various fuel-oxygen mixtures using the 4-Step combustion model and detailed chemical kinetic mechanisms (USC, Konnov, GRI 3.0).

Figure 5: Detonation re-initiation following its interaction with an obstacle, using 4-step chemistry (left) and compared to experiment (right).

Prospective Students

I am always looking for talented and motivated students, who are interested in pursuing graduate degrees, to work in my lab. Open positions in my lab are subject to available funding. Applicants are encouraged to email me to discuss a potential projects prior to applying to our graduate program.

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