Numerical investigation on the ignition and flame characteristics of n-dodecane-n-butanol spray under diesel engine conditions

Abstract

In this work, the ignition and flame characteristics of pure n-dodecane (Bu0) and its blends with n-butanol at 20% (Bu20) and 40% (Bu40) volume fraction at ambient temperatures of 800 K, 850 K and 900 K are numerically investigated under diesel engine conditions. Results show that n-dodecane-n-butanol blend undergo a two-stage ignition regardless of n-butanol blending ratio and ambient temperature. The first-stage ignition site is located at the spray periphery for all test cases except for Bu20 at 800 K. However, the second-stage ignition site moves to the spray head for all test cases but it remains at the spray periphery for Bu0. The mass fractions of formaldehyde (CH2O), hydroxyl radical (OH), hydroperoxyl (HO2) and hydrogen peroxide (H2O2) species at quasi-steady state are also slightly shifted to the fuel-lean region at higher n-butanol blending ratio and lower ambient temperature. Furthermore, the longer ignition delay at higher n-butanol blending ratio and lower ambient temperature leads to a wider distribution of the low-temperature combustion (M-LTC) mode. Meanwhile, the high-temperature combustion (M-HTC) and high-temperature diffusion combustion (M-HTC-diff) modes appear and are dominant from the second-stage ignition onwards.