An experimental study of influence of differential diffusion on speeds of H2/O2/Ar turbulent flames

Journal article, 2026

Growing interest in developing a closed-cycle internal combustion engine (ICE) that operates with hydrogen, oxygen, and argon motivates research into lean H₂/O₂/Ar turbulent flames. Accordingly, new experiments with confined statistically spherical turbulent flames expanding in lean (the equivalence ratio is equal to 0.45) H₂/O₂/Ar mixtures under different pressures and temperatures are performed using high-speed Schlieren technique and a fan-stirred combustion vessel. Measured data show that an increase in turbulent flame speed due to diffusional-thermal effects is more pronounced in H₂/O₂/Ar mixtures when compared to H₂/O₂/N₂ ones under comparable conditions (close values of laminar flame speeds or thicknesses and the same turbulent flow). However, differences in the effect magnitudes are quite moderate (20% or smaller), thus implying that models developed for lean hydrogen-air turbulent flames are suitable for H₂/O₂/Ar mixtures also. Specifically, analyses of the present and previously measured data obtained from CH₄-air, H₂/N₂/O₂, and H₂/O₂/He turbulent flames using the same experimental setup show that leading point concept performs well in all mixtures investigated. These results not only extend validation of the concept to mixtures that contain He or Ar but also suggest recommending the concept for numerically modeling turbulent burning in a closed-cycle ICE that operates with H₂, O₂, and Ar.