Estimation of NOx and soot emission from a constant volume n-butanol/n-dodecane blended spray using unsteady flamelet model based on n-dodecane/n-butanol/NOx/PAH chemistry

Abstract

A 246 species and 1062 reactions containing skeletal n-dodecane/n-butanol/NOx/Polycyclic Aromatic Hydrocarbon (PAH) combustion mechanism (Mix246) was developed for n-dodecane/n-butanol blend combustion under diesel engine-like conditions. The Mix246 mechanism was validated using ignition delay and species concentration profile data from various n-dodecane and n-butanol combustion experiments as well as by comparisons with predictions from the parent mechanisms. Subsequently, the Mix246 mechanism was coupled with a 3D Computational Fluid Dynamic (CFD) solver to simulate turbulent combustion of n-butanol/n-dodecane blended sprays in a constant volume combustor using an unsteady flamelet model. The CFD model for the 100% n-dodecane case was benchmarked against the non-reacting and reacting Spray-A conditions of the Engine Combustion Network (ECN). Finally, a parametric study was conducted to investigate the effects of various diesel engine-like conditions such as fuel injection pressure, initial ambient pressure and temperature conditions and varying n-butanol/n-dodecane blend ratios on NOx and soot emissions. Simulations show that the turbulent spray combustion evolves through distinct temporal stages and that the fully developed flame have spatially separated zones of reactive physics. Combustion properties and emission profiles for pure n-dodecane and blends with up to 20% n-butanol were seen to be nearly identical suggesting that n-butanol is a suitable alternative biofuel for CI engine combustion.