Multi-zone model for reactivity controlled compression ignition engine based on CFD approach

Abstract

RCCI (Reactivity controlled compression ignition) combustion is a novel and promising strategy in reducing soot and NOx emissions while obtaining diesel-like efficiencies. In this study, at first, a CFD (computational fluid dynamic) model is developed for RCCI engines simulation using semi-detailed chemical kinetics mechanism. N-heptane is injected directly into the combustion chamber as a high reactivity fuel while the low reactivity fuel, methane, is introduced as a premixed charge. The results of CFD investigations show significant differences between the injected and evaporated n-heptane. The CFD model is used to predict the evaporated n-heptane stratification. In the second part, a MMZM (modified multi zone model) is developed for RCCI engines simulation. The model contains both heat and mass transfer phenomena which are considered between all zones. The predicted n-heptane fuel stratification is introduced to the MZM (multi zone model). Semi detailed chemical kinetics mechanism is used for combustion simulation. A zero-dimensional single zone model, which is coupled to the MZM, is used to calculate the initial conditions and to model the gas exchange process. The simulation results are validated in a wide range of engine part loads operating conditions. The new way of introducing the evaporated fuel (direct injected) to each zone together with accurate heat and mass transfer models caused to accurate prediction of engine combustion and emission characteristics by MMZM. The MMZM can predict the SOC (start of combustion) and CA50 with sufficient accuracy. A maximum deviation of 1.5 CAD is observed comparing to the experimental results.