A study of liquid fuel injection and combustion in a constant volume vessel at diesel engine conditions

Experiments were performed in a constant volume vessel, with fuel sprays injected into the vessel at selected pressure and temperature conditions that are typical of a diesel engine at cold start. N-heptane and i-octane were used as surrogate fuels for diesel and gasoline, following the establishment of a semi-detailed mechanism containing skeletal mechanisms for n-heptane and i-octane, that has proved to predict autoignition delay times that agree well with experiments. Computational Fluid Dynamics (CFD) modeling of combustion for these two fuels at the selected experimental conditions were thus conducted adopting this mechanism, with the objective of studying fuel composition, temperature and pressure effects on mixing and combustion numerically. A tabulated chemistry approach called Flamelet Generated Manifolds (FGMs) has been applied for combustion modeling in the CFD solver STAR-CD. Since diesel combustion features mainly diffusion combustion, the manifold is created with 1D diffusion flame solutions from ignition and extended to steady state flamelets from low-to-high stretch rates. Effects from different fuels are examined experimentally, while effects from different conditions for n-heptane injection are examined from both experimental and simulation results.