Differential diffusion effects in the near field of non-premixed NH3/H2/N2-air jet flames at elevated pressure.

• Experimental investigation of differential diffusion effects in NH3-H2-N2 jet flames using 1D quantitative Raman scattering measurements. • Introduction of a diff-diff parameter for ammonia combustion, providing a quantitative measure of the differential diffusion effects. • Identification of strong differential diffusion in the near field of turbulent flames, up to an axial distance of 10 diameters. • Influence of NH3 cracking ratio on the diff-diff parameter, with higher ratios leading to increased differential diffusion, particularly in the low-temperature region. • Persistence of differential diffusion effects in the far field, as reflected in NH3/H2 profiles converging to a Le = 1-like profile with an increased NH3/H2 ratio. Differential diffusion (diff-diff) effects are analyzed in both non-premixed laminar and turbulent NH 3 -H 2 -N 2 jet flames at 5 bar using 1D quantitative Raman scattering measurements. The two target flames feature fuel compositions simulating a 14% and a 28% NH 3 cracking ratio. A diff-diff parameter is introduced for ammonia combustion, analogous to the definition used for hydrocarbon flames. Measurements in laminar flames, compared to Chemkin simulation featuring multi-component transport show that the instrument is capable of measuring the mean diff-diff parameter, but that single-shot measurements are compromised by the large sensitivity of the parameter to errors in N 2 and NH 3 mass fractions. The analysis of the diff-diff parameter in turbulent flames shows that both flames have strong differential diffusion in the near field up to an axial distance of 10 diameters (Z/D = 10), then the turbulent mixing becomes dominant further downstream. The flame with a 28% NH 3 cracking ratio exhibits a higher diff-diff parameter especially in the low-temperature region (<1000 K) due to the higher H 2 content. The competition between differential diffusion and turbulent mixing in the near field is also reflected in the NH 3 , H 2 , and NH 3 /H 2 profiles, falling in between prediction for Le = 1 and multi-component transport. Interestingly the NH 3 /H 2 profiles in the far field converge to a profile matching that of Le = 1, but with an increased NH 3 /H 2 ratio, showing the persistence of the differential diffusion effects in the region dominated by turbulent mixing. [ABSTRACT FROM AUTHOR]