In this paper, the basic combustion characteristics of blends of ammonia and several typical hydrocarbon fuels (including n-heptane, gasoline and RP-3 kerosene) are explored. The results show that the Laminar Flame Speed (LFS) of ammonia combustion assisted by n-heptane is faster than that of the ammonia combustion assisted by gasoline. The equivalent ratio of RP-3 kerosene/ammonia co-combustion corresponding to the highest LFS is evidently higher than other two fuels, and its equivalent ratio of lean burn limit is also higher. Further analysis of chemical reaction kinetics reveals that carbon-based fuels and ammonia interact with each other primarily via the competition to obtain active free radicals, such as OH, H, and O. Besides, the strength of C-N cross-reaction is relatively low and has little influence on the overall reaction path. Comparing the three co-combustion processes, the Markstein length of RP-3 kerosene-assisted ammonia combustion is higher, which is conducive to improving the stability of flame, especially under the high equivalent ratio. With the variation of temperature, the Markstein length of the n-heptane assisted ammonia combustion changes most significantly, and the addition of iso-alkanes will weaken the sensitivity of Markstein length to temperature.
Cellular instability of spherically expanding methanol/air flames was investigated in a constant-volume single-chamber cylindrical combustion vessel at initial temperatures of 373–423 K, initial pressures of 1–10 atm and equivalence ratios of 0.7–2.1. Flame morphology shows that the methanol/air flames suffer from cellular instability, especially at 5–10 atm. Stability analysis was performed to determine the logarithmic growth rate of disturbance, the critical Peclet number and the critical flame radius. The influences of initial temperature, initial pressure and equivalence ratio on cellular instability were analyzed to identify the influential factors. Both experimental results and stability analysis indicate cellular instability monotonically increases with increasing temperature or pressure and non-monotonically varies with increasing equivalence ratio. The reduced critical Peclet number and flame thickness slightly destabilize the flame surface as temperature increases. The almost unchanged critical Peclet number and the greatly reduced flame thickness with increasing pressure make the critical flame radius smaller and the flame surface more unstable at high pressures. The monotonically decreased critical Peclet number and the non-monotonically varied flame thickness result in the non-monotonic variation of cellular instability in methanol/air flames versus equivalence ratio. The critical flame radius consequently increases with increasing equivalence ratio under very rich conditions, while the corresponding flame surface becomes more smooth. The non-monotonic variation of cellular instability versus equivalence ratio is anticipated to exist widely in combustion of heavy fuels .
Laminar flame speeds of hexene isomers (1-hexene, 2-hexene and 3-hexene) and n-hexane are investigated at equivalence ratios of 0.8–1.5, initial temperatures of 373–453 K and initial pressures of 0.1–0.5 MPa using a constant volume combustion chamber . Results show that laminar flame speeds of hexene isomers are similar to each other and higher than those of n-hexane. NUI model, Fan model and LLNL model are validated against the experimental data. Simulation results of NUI model and Fan model agree well with experimental data while results of LLNL model show large discrepancies. The discrepancies between hexene isomers and n-hexane are mainly caused by thermal effect. Reaction pathway analysis shows that hexene isomers undergo similar reactions including H-abstraction reactions, radical-addition reactions and unimolecular decomposition reactions . Sensitivity analysis also reveals that the sensitivity coefficients of fuel specific reactions of hexene isomers are close to each other on the whole.
危险品化学品经营许可证（带存储）