Matei Ioan Radulescu

• Professor
• Professor at University of Ottawa

This research explores the final phase of the Deflagration-to-Detonation Transition (DDT) in methane-hydrogen-oxygen mixtures, combining both experimental observations and numerical modeling. The study identifies two distinct patterns of detonation re-initiation: for mixtures with a lower proportion of fuel, detonations that initially extinguish ca...

We address the problem of shock-induced ignition and transition to detonation in a reactive medium in the presence of mechanically induced fluctuations by a moving oscillating piston. For the inert problem prior to ignition, we provide a novel closed-form model in Lagrangian coordinates for the generation of the train of compression and expansions,...

This study investigates the role of two inert mono-atomic diluents, argon and helium, on the detonation structure in order to assess the importance of vibrational non-equilibrium and wall losses. When relaxation effects and wall losses are neglected, the detonation waves in mixtures diluted with either of these gases have the same kinetics, Mach nu...

Hydrogen, as a favored energy carrier for a sustainable, low-carbon future, poses safety concerns associated with its storage, transportation, and use that necessitates careful consideration. It is notably flammable when mixed with air over a wide spectrum of concentrations compared to natural gas. To complicate matters, there is a lack of extensiv...

A numerical simulation of an annular rotating detonation engine with stoichiometric hydrogen–oxygen is performed. A generic, well-posed, and easily implemented approach using a quasi-two-dimensional method to model the area variations through the rotating detonation engine’s injector and combustor is presented. The detonation–injector interaction i...

The present work revisited the detonation diffraction phenomenon from the D-κ perspective. By applying the curved ray-tracking method to post-process the critical diffraction experiments of hydrogen-oxygen-argon detonations, a system of shock rays was constructed. The detonation normal speed along rays and also the front curvature in each ray tube...

The present work examined the shock dynamics (i.e., speed, acceleration and front curvature) of detonations during sub-critical diffraction, where the complete quenching events eventually took place for the initially coupled shock-reaction complex. The compiled dynamics results showed that, while the ray-tube-based D(κ) relationships of detonations...

The present work reports new experiments of detonation diffraction in a 2D channel configuration in stoichiometric mixtures of ethylene, ethane, and methane with oxygen as oxidizer. The flow field details are obtained using high-speed schlieren near the critical conditions of diffraction. The critical initial pressure for successful diffraction is...

The present work reports new experiments of detonation diffraction in a 2D channel configuration in stoichiometric mixtures of ethylene, ethane, and methane with oxygen as oxidizer. The flow field details are obtained using high-speed schlieren near the critical conditions of diffraction. The critical initial pressure for successful diffraction is...

We first address the problem of initiation behind decaying shock waves analytically and numerically. The ignition along a particle path crossing the shock is analysed in terms of its volumetric expansion, evaluated as a function of the shock strength, decay rate, and curvature using the shock change equations. Closed form solutions are derived for...

We review the concept of critical explosion length 0 as a unique length scale characterizing the detonability of a reactive mixture. Review of empirical data for methane and hydrogen fuels in various compositions with air or O2/N2 supports that this length scale in critically initiated detonations by a strong energy source (direct initiation) coinc...

Current analyses of curved detonations are mostly limited to the dynamics along the wall or the symmetric axis, due to a lack of efficient approaches for reliably tracking stream tubes with curved shock fronts. To address this lack, the present work proposes a novel curved ray-tracking algorithm with two implementation methods. The curved ray is ch...

This study uses a simplified detonation model to investigate the behavior of detonations with galloping-like pulsations. The reactive Burgers equation is used for the hydrodynamic equation, coupled to a pulsed source whereby all the shocked reactants are simultaneously consumed at fixed time intervals. The model mimics the short periodic amplificat...

An incorrect model exponent derived from Whitham’s characteristic rule was used by Yuan et al. (Shock Waves 30:13–27, 2020) to predict the dynamics of detonation diffraction and re-initiation. In this comment, the correct value is presented and the impact of this error is evaluated.

One strategy for arresting propagating detonation waves in pipes is by imposing a sudden area enlargement, which provides a rapid lateral divergence of the gases in the reaction zone and attenuates the leading shock. For sufficiently small tube diameter, the detonation decays to a deflagration and the shock decays to negligible strengths. This is k...

One strategy for arresting propagating detonation waves in pipes is by imposing a sudden area enlargement, which provides a rapid lateral divergence of the gases in the reaction zone and attenuates the leading shock. For sufficiently small tube diameter, the detonation decays to a deflagration and the shock decays to negligible strengths. This is k...

We evaluate the effect of boundary layer losses on two-dimensional H2/O2/Ar cellular detonations obtained in narrow channels. The experiments provide the details of the cellular structure and the detonation speed deficits from the ideal CJ speed. We model the effect of the boundary layer losses by incorporating the flow divergence in the third dime...

The present work examines the role of instability and diffusive phenomena in controlling the limits of detonations subject to lateral strain. Experiments were conducted in mixtures with varying levels of cellular instability, i.e., stoichiometric methane–oxygen (CH4/2O2), ethylene–oxygen (C2H4/3O2), and ethane–oxygen (C2H6/3.5O2). These detonations...

The present study aims to clarify the effect of the polytropic index (i.e., the ratio of specific heats in the context of a perfect gas) on the detonation structure. This is addressed by two-dimensional numerical simulations. To ease the clarification of the role of gasdynamics, a simple Arrhenius kinetic law is used for the chemical model. The act...

We show experimentally and numerically that when a weak shock interacts with a finger flame in a narrow channel, an extremely efficient mechanism for deflagration to detonation transition occurs. This is demonstrated in a 19-mm-thick channel in hydrogen-air mixtures at pressures below 0.2 atm and weak shocks of Mach numbers 1.5 to 2. The mechanism...

Shock flame interactions are fundamental problems in many combustion applications ranging from flame acceleration to flame control in supersonic propulsion applications. The present paper seeks to quantify the rate of deformation of the flame surface and burning velocity caused by the interaction and to clarify the underlying mechanisms. The intera...

Shock reflection experiments are performed to study the large-scale convective mixing created by the forward jetting phenomenon. Experiments are performed at a wedge angle of $\theta_{\mathrm{w}} = 30^{\circ}$ in nitrogen, propane-oxygen, and hexane with incident shock Mach numbers up to $M = 4$. Experiments are complimented by shock-resolved visco...

The numerical simulation of a rotating detonation engine consisting of a plenum, injector and combustor is performed for stoichiometric hydrogen-oxygen. A generic approach to model the area variations in the injector, using a quasi-two-dimensional method, is presented . The case with an area ratio of four between the combustor and injector's throat...

The present study aims to clarify the effect of the polytropic index (i.e., the ratio of specific heats in the context of a perfect gas) on the detonation structure. This is addressed by two-dimensional numerical simulations. To ease the clarification of the role of gasdynamics, a simple Arrhenius kinetic law is used for the chemical model. The act...

This study uses a simplified detonation model to investigate the behaviour of detonations with galloping-like pulsations. The reactive Burgers equation is used for the hydrodynamic equation, coupled to a pulsed source whereby all the shocked reactants are simultaneously consumed at fixed time intervals. The model mimics the short periodic amplifica...

The present work revisits the problem of modeling the real gaseous detonation dynamics at the macro-scale by simple steady one-dimensional (1D) models. Experiments of detonations propagating in channels with exponentially expanding cross-sections were conducted in the H2/O2/Ar reactive system. Steady detonation waves were obtained at the macro-scal...

While the compressible flow theory has relied on the perfect gas model as its workhorse for the past century, compressible dynamics in dense gases, solids, and liquids have relied on many complex equations of state, yielding limited insight into the hydrodynamic aspect of the problems solved. Recently, Le Métayer and Saurel studied a simple yet pro...

We revisit and derive the shock change equations relating the dynamics of a shock wave with the partial derivatives describing the motion of a reactive fluid with the general equation of state in a stream-tube with arbitrary area variation. We specialize these to a perfect gas in which we obtain all shock change equations in closed form. These are...

We revisit and derive the shock-change equations relating the dynamics of a shock wave with the partial derivatives describing the motion of a reactive fluid with general equation of state in a stream-tube with arbitrary area variation. We specialize these to a perfect gas, in which we obtain all shock-change equations in closed form. These are fur...

While compressible flow theory has relied on the perfect gas model as its workhorse for the past century, compressible dynamics in dense gases, solids and liquids have relied on many complex equations of state, yielding limited insight on the hydrodynamic aspect of the problems solved. Recently, Le M\'etayer and Saurel studied a simple yet promisin...

The present work examines the role of instability and diffusive phenomena in controlling the limits of detonations subject to lateral strain rates. Experiments were conducted in hydrocarbon-oxygen mixtures with varying levels of cellular instability. These detonations were propagated in channels with exponentially enlarging cross-sections, followin...

The present study is an experimental investigation of the last stages of the deflagration-to-detonation transition. A fast flame following a lead shock was generated by passing a detonation wave through a perforated plate. The shock flame complex then interacts with an obstacle of different shape. We study the influence of the obstacle shape on the...

We show experimentally and numerically that when a weak shock interacts with a finger flame in a narrow channel, an extremely efficient mechanism for deflagration to detonation transition occurs. This is demonstrated in a 19-mm-thick channel in hydrogen-air mixtures at pressures below 0.2 atm and weak shocks of Mach numbers 1.5 to 2. The mechanism...

We evaluate the effect of boundary layer losses on two-dimensional H2/O2/Ar cellular detonations obtained in narrow channels. The experiments provide the details of the cellular structure and the detonation speed deficits from the ideal CJ speed. We model the effect of the boundary layer losses by incorporating the flow divergence in the third dime...

The inviscid hydrodynamics of inert compressible media governed by the Euler equations of motion only require knowledge of a caloric equation of state e(p, v) for the material relating the internal energy e to the fluid pressure p and specific volume v (or density). For departures from the ideal gas behavior, simple equations of state such as the s...

Previous experiments have revealed that shock waves driven through dissipative media may become unstable, for example, in granular gases, and in molecular gases undergoing strong relaxation effects. The current paper addresses this problem of shock stability at the Euler and Navier–Stokes continuum levels in a system of disks (two-dimensional) unde...

The present study investigates and addresses the influence of non-equilibrium effects on thermal ignition problems using molecular dynamics simulations. The ignition delay calculations were compared with those obtained at the continuum level using rates derived from kinetic theory: the standard rate assuming that the distribution of the speed of th...

The present study addresses the role of molecular non-equilibrium effects in thermal ignition problems. We consider a single binary reaction of the form A+B → C+C. Molecular dynamics calculations were performed for activation energies ranging between RT and 7.5RT and heat release of 2.5RT and 10RT. The evolution of up to 10,000 particles was calcul...

It is found that the threshold for blast-induced neurotrauma documented from previous experiments in animals and cell cultures is approximately given by the criterion that the shock thickness be comparable to the characteristic dimension of a neuron cell (approximately 20 μm). The coincidence of the shock thickness with the characteristic dimension...

The present work revisits the problem of modelling the real gaseous detonation dynamics at the macro-scale by simple steady one-dimensional (1D) models. Experiments of detonations propagating in channels with exponentially expanding cross-sections (exponential horns) were conducted in the H2/O2/Ar reactive system. Steady detonation waves were obtai...

Forward jetting and Mach stem bifurcation of irregular shock reflections are studied numerically and experimentally for a wedge angle of 30°. Simulations of the Navier-Stokes equations, resolving the shock width, show increasing Mach stem bulging with Mach number and decreasing isentropic exponent. Experiments in rich propane-oxygen and in hexane a...

The present paper seeks to determine the mechanism of flame acceleration and transition to detonation when a turbulent flame preceded by a shock interacts with a single obstruction in its path, taken as a cylindrical obstacle or a wall in the present study. The problem is addressed experimentally in a mixture of propane-oxygen at sub-atmospheric co...

The present paper seeks to determine the mechanism of flame acceleration and transition to detonation when a turbulent flame preceded by a shock interacts with a single obstruction in its path, taken as a cylindrical obstacle or a wall in the present study. The problem is addressed experimentally in a mixture of propane-oxygen at sub-atmospheric co...

Experiments conducted over the past several decades have shown that the cellular structure of detonations is responsible for enhancing the detonability of gaseous detonations in the presence of losses, as compared with that predicted by the classical Zel'dovich-Von Neuman-Döring model for detonations, which neglects the time varying cellular struct...

In the current study, the influence of turbulent mixing and local reaction rates on the transition to detonation of a turbulent shock-flame complex was investigated using a large eddy simulation (LES) strategy. Specifically, detonation attenuation by a porous medium, and the subsequent re-initiation for methane-oxygen, a moderately unstable mixture...

In the current study, the influence of turbulent mixing and local reaction rates on the transition to detonation of a turbulent shock-flame complex was investigated using a state-of-the-art large eddy simulation (LES) strategy. Specifically, detonation attenuation by a porous medium, and the subsequent re-initiation for methane–oxygen, a moderately...

The present study addresses the role of molecular non-equilibrium effects in thermal ignition problems. We consider a single binary reaction of the form A+B -> C+C. Molecular dynamics calculations were performed for activation energies ranging between RT and 7.5RT and heat release of 2.5RT and 10RT. The evolution of up to 10,000 particles was calcu...

Steady one-dimensional numerical simulations were performed to investigate the dynamics of the ZND detonation propagating in dimethyl ether- oxygen-carbon dioxide (DME-O2-CO2) mixtures. For dilution level as low as 70%, the chemical pathways characteristic of low-temperature and intermediate-temperature hydrocarbon fuels chemistry were activated. T...

In the current study, the influence of turbulent mixing and local reaction rates on the transition to detonation of a turbulent shock-flame complex was investigated using a state-of-the-art large eddy simulation (LES) strategy. Specifically, detonation attenuation by a porous medium, and the subsequent re-initiation for methane–oxygen, a moderately...

Despite six decades of extensive investigation, the detonation diffraction critical conditions have not yet been predicted from first principles and only semi-empirical models are available to estimate the critical tube diameter. The present study aims at providing a well-defined experimental and numerical framework to help establishing a quantitat...

The present study addresses the reaction zone structure and burning mechanism of unstable detonations. Experiments investigated mainly two-dimensional methane-oxygen cellular detonations in a thin channel geometry. The sufficiently high temporal resolution permitted to determine the PDF of the shock distribution, a power-law with an exponent of -3,...

The problem of thermal ignition in a homogeneous gas is revisited from a molecular dynamics perspective. A two-dimensional model is adopted, which assumes reactive disks of types A and B in a fixed domain that react to form type C products if an activation threshold for impact is surpassed. Such a reaction liberates kinetic energy to the product pa...

Recently, thin-channel experiments and 2D simulations have been conducted in order to investigate the effect of turbulent mixing rates on the structure of irregular detonation wave propagation. Furthermore, the dependence of the observed cell pattern, and also the reaction zone thickness, on the mixing of burned products with pockets of unburned ga...

Previous experiments have revealed that shock waves driven through dissipative gases may become unstable, for example, in granular gases. The mechanisms controlling these instabilities are not well understood. Two-dimensional event-driven Molecular Dynamics (MD) simulations were previously completed to investigate the stability of piston driven sho...

The present study addresses the reaction zone structure and burning mechanism of unstable detonations. Experiments investigated mainly two-dimensional methane-oxygen cellular detonations in a thin channel geometry. The sufficiently high temporal resolution permitted to determine the PDF of the shock distribution, a power-law with an exponent of -3,...

The problem of thermal ignition in a homogeneous gas is revisited from a molecular dynamics perspective. A two-dimensional model is adopted, which assumes reactive disks of type A and B in a fixed area that react to form type C products if an activation threshold for impact is surpassed. Such a reaction liberates kinetic energy to the product parti...

The reflection of a triple-shock configuration was studied numerically in two dimensions using the Navier-Stokes equations. The flow field was initialized using three shock theory, and the reflection of the triple point on a plane of symmetry was studied. The conditions simulated a stoichiometric methane-oxygen detonation cell at low pressure on ti...

The present work addresses the question of whether mean field macroscopic models are suitable to describe the dynamics of real cellular detonations. This question is posed in the framework of detonations with stream-tube area divergence that is kept constant, as to generate attenuated detonations in quasi-steady state. An exponential horn geometry...

An exponential horn geometry is introduced in order to establish cellular detonations with a constant mean lateral mass divergence, propagating at quasi-steady speeds below the Chapman-Jouguet value. Experiments and simulations demonstrated that such quasi-steady state detonations can be realized, hence permitting to obtain the relations between th...

The reflection of a triple-shock configuration was studied numerically in two dimensions using the Navier-Stokes equations. The flow field was initialized using three shock theory, and the reflection of the triple point on a plane of symmetry was studied. The conditions simulated a stoichiometric methane-oxygen detonation cell at low pressure on ti...

Experiments and numerical simulations have been conducted in order to investigate the effect of turbulent mixing rates on the overall structure of irregular detonation wave propagation. The dependence of the observed cell pattern regularity and size, and also the reaction zone thickness, on the mixing of burned products with pockets of unburned gas...

We study experimentally fast flames and their transition to detonation in mixtures of methane, ethane, ethylene, acetylene, and propane mixtures with oxygen. Following the interaction of a detonation wave with a column of cylinders of varying blockage ratio, the experiments demonstrate that the fast flames established are Chapman-Jouguet deflagrati...

We study experimentally fast flames and their transition to detonation in mixtures of methane, ethane, ethylene, acetylene, and propane mixtures with oxygen. Following the interaction of a detonation wave with a column of cylinders of varying blockage ratio, the experiments demonstrate that the fast flames established are Chapman-Jouguet deflagrati...

A turbulent combustion subgrid model, inspired by the Linear Eddy Model for Large Eddy Simulation (LEM-LES), is developed to study highly compressible and reactive flows involving very rapid transients in pressure and energy. The model is intended to be a one-dimensional treatment of a diffusion-reaction system within a multi-dimensional LES cell....

Turbulent and unstable detonation propagation is modelled using the Compressible-Linear Eddy Model for Large Eddy Simulation (CLEM-LES); a novel combustion modelling strategy which treats highly compressible and reactive flows involving very rapid transients in pressure and energy. A major challenge of modelling unstable detonation propagation is t...

In the present work the propagation of gaseous detonations in a channel with porous walls is investigated experimentally and numerically. The main goal of the study is to determine the role of diffusive turbulent mixing and transverse waves in controlling the detonation limits in channels with porous walls. Detonations in propane–oxygen and hydroge...

This paper examines the dynamics of unconfined hydrogen–air flames and the criterion for flame propagation between neighbouring pockets of reactive gas separated by air using the soap bubble technique. The combustion events were visualized using high-speed schlieren or large-scale shadowgraph systems. It was revealed that for sufficiently lean hydr...

A turbulent combustion model based on the Linear Eddy Model for Large Eddy Simulation (LEM-LES) has been developed to study highly compressible and reactive flows involving very rapid transients in pressure and energy. In the current work, the model is used to simulate 2D unsteady and turbulent detonation propagation, in a narrow channel, which inv...

The study investigates detonations with multiple quasi-steady velocities that have been observed in the past in systems with multi-peaked thermicity, using Fickett's detonation analogue. A steady state analysis of the travelling wave predicts multiple states, however, all but the one with the highest velocity develop a singularity after the sonic p...

Previous experiments have revealed that shock waves driven through dissipative gases may become unstable, for example, in granular gases and in molecular gases undergoing strong relaxation effects. The mechanisms controlling these instabilities are not well understood. We successfully isolated and investigated this instability in the canonical prob...

The detonation wave stability is addressed using Fickett's equation, i.e., the reactive form of Burgers' equation. This serves as a simple analogue to the reactive Euler equations, permitting one to gain insight into the nonlinear dynamics of detonation waves. Chemical kinetics were modeled using a two-step reaction with distinct induction and reac...

Shocks in granular media have been shown to develop instabilities. We address the role that early stages of shock development have on this type of instability. We look at the evolution of shock waves driven by a piston in a dilute system of smooth inelastic disks, using both discrete particle and continuum modelling. To mimic a realistic granular g...

A turbulent combustion model based on the Linear Eddy Model for Large Eddy Simulation (LEM-LES) has been developed to study highly compressible and reactive flows involving very rapid transients in pressure and energy. The model is treated as a one-dimensional sample of a diffusion-reaction system within each multi-dimensional LES cell. This reduce...

The purpose of this study is to determine the performance of a portable large-scale shadowgraph system for use in hydrogen combustion experiments. Previous large-scale shadowgraph and schlieren implementations have often been limited to background-oriented techniques which are subject to noise. The system built is based on a large-scale shadowgraph...

A turbulent combustion model based on the Linear Eddy Model for Large Eddy Simulation (LEM-LES) (Menon, 2011) is currently being developed to study highly compressible and reactive flows involving very rapid transients in pressure and energy. The model is a one-dimensional treatment of a diffusion-reaction system within each multi-dimensional LES c...

A turbulent combustion model based on the Linear Eddy Model for Large Eddy Simulation (LEM-LES) has been developed to study highly compressible and reactive flows involving very rapid transients in pressure and energy. The model is treated as a one- dimensional sample of a diffusion-reaction system within each multi-dimensional LES cell. This reduc...

In the present study, pressure waves generated by a metastable intermolecular composite (MIC) have been measured experimentally in an aqueous environment and correlated with flame speed measurements. Underwater experiments were performed in a 1.0 L high-pressure chamber mounted with high-resolution pressure transducers and designed with optical acc...

The present study focused on the cold gas dynamic spray process for manufacturing porosity free, finely structured energetic materials with high reactivity and structural integrity. The experiments have focused the reaction between the aluminium and metal oxide, such as Al-CuO system. The consolidation of the materials used the cold gas dynamic spr...

It has been shown that the cold-gas dynamic spraying process, or simply cold spray, is a suitable technique to manufacture nanoscale energetic materials with high reactivity and low porosity. The current study focuses on the Ni-Al system, for which the reactivity has been increased by an initial mechanical activation achieved by the ball-milling te...

Using Fickett’s model for reactive compressible flows, i.e., the reactive form of Burgers’ equation, we address the problem of shock induced ignition by a piston in a reactive medium characterized by a 2 step induction-reaction kinetics. Owing to the model’s simplicity, the ignition and acceleration mechanism is explained using the two families of...