A Mean-Value Model of a Turbocharged HCCI Diesel Engine with External Mixture Formation

Homogeneous Charge Compression Ignition (HCCI) is currently considered one of the most promising concepts to achieve low NO_x and particulate matter emissions in traditional Compression Ignition Direct Injection (CIDI) engines. In spite of these benefits, understanding and controlling the complex mechanisms which govern the onset of combustion process are still extremely difficult, especially because there is little or no direct control on the combustion development as in Spark Ignition or Compression Ignition engines.

The proposed paper describes a mean-value model of a HCCI Diesel engine with external mixture formation fitted with Variable Geometry Turbocharger, Intercooler and Cooled EGR. The effort is aimed at understanding and controlling the complex combustion phenomena in order to identify the influence of the control parameters on the auto-ignition process. The overall structure is a 6-state model in the continuous time domain, which supports a discrete-event, calculation of the combustion process. The in-cylinder processes are estimated through a single-zone, first-law approach based on the definition of a Heat Release Rate (HRR) function. The model is then validated against experimental data collected on a Diesel engine modified to operate in HCCI mode with external mixture preparation.