System Level Engine Modeling for HCCI Engine Control during Thermal Transients

Abstract:
This computational study addresses the effects of thermal inertia on combustion in an HCCI engine. The role of wall temperatures and residual gases on HCCI combustion during steady state and transient operation is studied in the framework of a 1-D cycle simulation linked with a thermal network model. This model is coupled with Simulink® to deal with control issues as well. The strong dependence of HCCI engine’s combustion phasing and performance on the thermal condition of the engine makes it necessary to control the engine using path dependent calibration of combustion parameters for best fuel economy and knock-free performance. This study includes simulating engine-in-vehicle and assessing critical transients in the engine speed-load map.

Background:
In order to combine the merits from SI and CI combustion concepts, Homogeneous Charge Compression Ignition (HCCI) emerged about 30 years ago. The combustion principle of HCCI engine is simultaneous multiple auto-ignition in cylinder with a spatially well-distributed (theoretically homogeneous) air fuel mixture. The basic idea is to employ a premixed air-fuel mixture that is sufficiently lean or dilute to keep flame temperatures below about 1900K to help keep NOx and particulate production low. This concept is regarded as a great candidate for future clean and economical passenger vehicle engine applications because of its high thermal efficiency, potentially 15-20% higher than conventional gasoline engine, and ultra low NOx and particulate matters emissions compared with SI and CI engines. However, commercializing an HCCI engine has not realized yet because a lot of challenges has been introduced in practical application of the concept. Among many challenges, the strong dependence of combustion characteristics of HCCI engine on the engine’s thermal condition is our focus to study in this project.

Computer Model - Component Map