Numerical Study On The Single-Zone And Multi-Zone Models Of HCCI Engine Combustion Process

The concept of Homogeneous Charge Compression Ignition (HCCI) is proposed to realize the goal of high thermal efficiency and low emission of engines and numerical simulation is being paid widely attention because of its efficiency and reliability.This study establishes single-zone and multi-zone models to simulate combustion process of HCCI engines with fuels of n-heptane. In this study, a single-zone model of HCCI combustion based on energy and mass equations is established and a detailed chemical kinetic mechanism is applied. The single-zone model is solved by SENKIN under specific conditions which is a program for predicting homogeneous gas-phase chemical kinetics in a closed system to obtain time-varing parameters like temperature, pressure and heat release rate, etc. Influences of inlet temperature, inlet pressure, equivalence rate, EGR, compression ratio and revolution on combustion characteristics are studied. Based on single-zone model, a multi-zone model is established with models of distribution of zones, heat transfer from the wall, mass exchange between zones and boundary layer. Parameters like temperature, mass, components, volume of each zone are calculated by SENKIN with separation solution. A comparison of influences of different sub-models and initial conditions on combustion and emission is studied. A simulation of HCCI engines combustion process is carried out with a nine zones model.The results based on simulation indicate that a separation of inner core has little effect on combustion characteristics and a separation of outer core can improve the accuracy of the emission simulation. Taking heat transfer from the wall and mass exchange between zones into consideration can predict combustion process accurately. Reducing the volume of crevice layer and improving the temperature of cylinder wall can reduce emission. HC is mainly produced in the crevice layer and boundary layer. CO is mainly produced in boundary layer and outer core. NO is mainly produced in inner cores.