Rémy Mével

One-dimensional simulations of head-on quenching CO2-diluted oxy-methane flames were performed over a wide range of pressures and CO2 dilution levels, encompassing operating conditions of both subcritical combustion and supercritical combustion in direct-fired supercritical carbon dioxide (sCO2) power cycles. Flame/wall interaction characteristics were analyzed in terms of quenching distance and wall heat flux. The quenching distance was found to increase with increasing CO2 dilution and decreasing pressure, whereas wall heat flux exhibited the opposite trend. After normalization using flame characteristic parameters, the normalized quenching distance, i.e., the quenching Peclet number, ranges from 0.2 to 0.6, and the normalized maximum wall heat flux from 0.4 to 0.9. The near-wall heat release behavior was further examined. Near-wall heat release enhancement was observed under conditions of low pressure and low CO2 dilution, primarily due to the radical recombination reaction between H and CH3 and hydrogen chain propagation reactions. Increasing CO2 dilution hinders radical transport to the wall, suppressing near-wall reactions. Increasing pressure affects the competition among low-activation-energy H-consumption channels through reduced species diffusivity and enhanced three-body reactions. Specifically, the H and CH3 recombination reaction is increasingly suppressed with pressure, whereas hydrogen chain propagation reactions are enhanced at low pressures but inhibited at high pressures. The occurrence of near-wall heat release enhancement was found to correlate strongly with the quenching Peclet number. A radical diffusion length scale is introduced, and near-wall heat release enhancement occurs only when the quenching distance is smaller than this length scale. A predictive criterion based on the Damköhler number is further proposed.

Liquid-fueled detonation has attracted considerable interest due to the high volumetric energy density of liquid fuels. In the present work, detonation wave propagation in n-dodecane droplets was investigated through two-dimensional simulations. The dispersed droplets were tracked based on the Lagrangian framework, while the continuous phase was solved in an Eulerian way. The Pilch–Erdman model was applied to account for droplet breakup. A detailed reaction mechanism was used for n-dodecane combustion. Three cases with different liquid equivalence ratios and oxygen mass fractions were considered. The simulation results of the detonation cell width were generally consistent with those of the experiment, with quantitative deviations of approximately 10%–40%. The droplet size distribution and breakup behavior were analyzed. It was shown that droplet breakup is the most pronounced behind the Mach stem. Three types of fuel droplets were identified behind the detonation front, i.e., droplets just shocked by the detonation front, shocked droplets progressively relaxing toward equilibrium with the surrounding gas, and small droplets associated with localized intense transverse detonations. Two distinct peaks were observed in the probability density functions of droplet diameter. In the case with low oxygen concentrations, a higher probability of smaller droplet diameters is identified. The liquid equivalence ratio has only a minor effect on the droplet diameter distribution. The statistical analysis of the leading front was conducted to characterize the detonation front dynamics. The leading front showed significant velocity deficits in all cases. It was found that the most probable velocities of the leading front decrease with increasing mass loading ratios. The joint probability density function of the detonation speed and the induction length was also examined, and a negative correlation between the two quantities was observed. Droplet breakup and evaporation significantly lengthen the induction zone to approximately 2–4 times that of the corresponding purely gaseous detonation.

The dynamics of detonation is governed by intrinsic longitudinal and transverse instabilities. This work fills the research gap of detonation stability at elevated pressure as real gas effects, including the finite molecular volume and inter-molecular attraction forces, become non-negligible. The stability of one-dimensional pulsating and two-dimensional cellular detonations at elevated pressure was investigated using both linear stability analysis and high-fidelity numerical simulations. For pulsating detonations, the neutral stability boundaries derived from the linear stability analysis reveal that the impact of real gas effects on detonation stability depends on the heat content. Specifically, real gas effects stabilise pulsating detonation at high heat content, destabilise it at intermediate levels and exhibit competing influences, i.e. destabilisation from finite molecular volume and stabilisation from the inter-molecular attraction force, at low heat content. For cellular detonations, a stability map is proposed in the Mach number–reduced activation energy plane, demonstrating that real gas effects stabilise detonation and lead to more regular cellular structures or even fully planar detonations. Theoretical predictions show good agreement with numerical simulations. An oscillator model was used to elucidate the interplay between the heat release and shock dynamics. It shows that the stabilising effect of real gas is associated with reduced velocity oscillation amplitude, increased phase lag between heat release and shock speed variations and lower values of the coupling parameter. The comprehensive linear stability analysis with complete real gas models is an effective predictive tool for the detonation dynamics at elevated pressure.

In this study, one-dimensional numerical simulations of normal detonation waves in aluminum/hydrogen/air mixtures were performed. A detailed two-stage model of aluminum particle combustion was employed, including the effects of interphase heat transfer, phase change, heterogeneous surface reaction, oxide cap growth, homogeneous combustion, and radiation. Five cases were considered to explore the effects of particle size on the detonation propagation, wave structure, and heat release characteristics. It was found that aluminum addition significantly enhances the detonation propagation speed compared to the purely gaseous case with hydrogen/air mixtures. Smaller aluminum particles exhibit a shorter combustion duration, featuring a higher propagation speed. A transient double-front structure can be observed for the case with a particle diameter larger than 2 μm, which eventually merges into a single detonation wave. Particle tracking analysis reveals that the release of gaseous aluminum upstream of the sonic point enhances homogeneous reactions in the reaction zone. Analysis of heat release indicates that hydrogen oxidation dominates the detonation wave, while gaseous aluminum combustion contributes evidently in the coupled stage, thereby enhancing the wave propagation speed.