Numerical study and correlation development on laminar burning velocities of n-butanol, iso-octane and their blends: Focusing on diluent and blend ratio effects

摘要

Bio-n-butanol as a potential alternative bio-fuel is accepted more and more attention presently in the fields of both scientific research and commercial market; however, n-butanol is impossible to substitute conventional fuels completely in the short and medium term. Therefore, understanding the premixed flame's characteristics of iso-octane-butanol mixture fuels is no doubt an important way to make better use of n-butanol as a fuel applied in conventional SI (spark-ignition) engines. On the other hand, the engines always operate with EGR (exhaust gas recirculation), so the premixed flame characteristics of fuels (pure fuels or iso-octane-butanol mixture fuels) are needed to be investigated under EGR operations. Driven by these facts, we performed a numerical study, which is validated by experimental data, on the laminar burning velocity of n-butanol, iso-octane and their blends. Based on this, correlations including the influences of diluent and fuel component blend ratio, respectively, are developed and their fitting parameters are resolved carefully through a wide range of dataset. From results, our correlations are sufficient in accuracy to describe the effects mentioned above. Within each effect, for deeper understanding the appearance influence on the laminar burning velocity, the deep mechanism of chemical kinetic effect is revealed and discussed. In particular, as diluent effect as concerned, each single diluent gas component, such as CO_2, H_2O, and N_2, is analyzed separately, the combined diluent effect can then be solved by grouping contributions brought by each species. In addition, our correlations were compared to those in literature widely. Concerning the mixture fuels, a correction factor is introduced by present study, such that the accuracies of mixing rules are improved at fuel-rich equivalence ratios.