Luiz Maltez Faria’s research while affiliated with University of Paris-Saclay and other places

The effect of heat and momentum losses on the steady solutions admitted by the reactive Euler equations with sink/source terms is examined for stoichiometric hydrogen–oxygen mixtures. Varying degrees of nitrogen and argon dilution are considered in order to access a wide range of effective activation energies, $E_{\textrm{a,eff}}/R_{\textrm{u}}T_{0}$ E a,eff / R u T 0 , when using detailed thermochemistry. The main results of the study are discussed via detonation velocity-friction coefficient ( D – $c_{\textrm{f}}$ c f ) curves. The influence of the mixture composition is assessed, and classical scaling for the prediction of the velocity deficits, $D(c_{\textrm{f,crit}})/D_{\textrm{CJ}}$ D ( c f,crit ) / D CJ , as a function of the effective activation energy, ${E}_{\textrm{a,eff}}/R_{\textrm{u}} T_{0}$ E a,eff / R u T 0 , is revisited. Notably, a map outlining the regions where set-valued solutions exist in the $E_{\textrm{a,eff}}/R_{\textrm{u}}T_{0}\text {--}{\alpha }$ E a,eff / R u T 0 -- α space is provided, with $\alpha$ α denoting the momentum–heat loss similarity factor, a free parameter in the current study.

The problem of the steady propagation of detonation waves with friction losses is revisited including detailed kinetics. The derived formulation is used to study the influence of chemical modeling on the steady solutions and reaction zone structures obtained for stoichiometric hydrogen-oxygen. Detonation velocity-friction coefficient (D − c f) curves, pressure, temperature , Mach number, thermicity and species profiles are used for that purpose. Results show that both simplified kinetic schemes considered (i.e., one-step and three-step chain-branching), fitted using standard methodologies, failed to quantitatively capture the critical c f values obtained with detailed kinetics; moreover one-step Arrhenius chemistry also exhibits qualitative differences for D/D CJ ≤ 0.55 due to an overestimation of the chemical time in this regime. An alternative fitting methodology for simplified kinetics is proposed using detailed chemistry D − c f curves as a target rather than constant volume delay times and ideal Zel'dovich-von Neumann-Döring profiles; this method is in principle more representative to study non-ideal detonation propagation. The sensitivity of the predicted critical c f value, c f,crit , to the detailed mechanisms routinely used to model hydrogen oxidation was also assessed; significant differences were found, mainly driven by the consumption/creation rate of the HO 2 radical pool at low postshock temperature.

A combined experimental and theoretical study of deflagration-to-detonation transition (DDT) in smooth narrow channels is presented. Some of the distinguishing features characterizing the late stages of DDT are shown to be qualitatively captured by a simple one-dimensional scalar equation. Inspection of the structure and stability of the traveling wave solutions found in the model, and comparison with experimental observations, suggest a possible mechanism responsible for front acceleration and transition to detonation.