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

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.