Influence of Blending n-Butanol with Isooctane and n-Heptane on Ignition Delay Times in a Fuel Ignition Tester

摘要

Experimental results on the ignition delay trends of n-heptane, isooctane, n-butanol, and the binary blends of n-butanol-heptane and n-butanol/isooctane are reported. Fuel sprays were injected into a quiescent, pressurized, and preheated air in a constant volume combustion chamber using the Waukesha Fuel Ignition Tester. The averaged initial oxidizer pressure and temperature were 24 bar and 812 K, respectively. The fuel injection duration was held constant at 5.0 ms. The results were used to obtain the dependence of the derived cetane number (DCN) on the volumetric fuel blending ratios. A monotonic, nonlinear reduction in reactivity of both n-heptane and isooctane was observed when blended with n-butanol, while a larger change in DCNs was observed for n-butanol-heptane blends than that for n-butanol/isooctane blends. The temperature dependence of the ignition delay times for the three neat fuel constituents were also obtained. Both first stage and overall ignition delay times are reported. In addition, global equivalence ratios were derived from exhaust gas composition measurements. Furthermore, the experimental ignition delay results of the blends and temperature dependence studies were compared to homogeneous zero-dimensional simulations based on the corresponding global equivalence ratios. Chemical kinetic models validated for autoignition of the aforementioned neat fuels and their blends were used in the simulations. The simulations indicate that homogeneous kinetics performs well for cases with long ignition delay times and also for a fuel exhibiting only single-stage ignition. This study provides insights into the influence of n-butanol blending on ignition delay time and emissions, and it provides information regarding the autoignition response of the pure fuel components for varying oxidizer temperatures.