Abstract
This work applies Large Eddy Simulation (LES) to the combustion process within a CAI engine. The chemical reaction is treated with a pre-tabulation approach based on homogeneous reactor simulations. At this juncture, a five-dimensional chemistry database is employed where the thermo-chemical properties are a function of the unburnt gas temperature, the air–fuel ratio, the exhaust gas ratio, the pressure, and the reaction progress variable. Statistical quantities are gathered for 20 simulated cycles and the averaged pressure curves get compared to measurements. The simulation data are then used to provide further insight into the auto-ignition process. It will be shown how thermo-chemical states are distributed within the cylinder and how the ignition quality depends on them. A statistical analysis is conducted to identify manifolds in the multi-dimensional scalar space along which the conditions leading to ignition evolve. Furthermore the strong influence in between consecutive cycles caused by the exhaust gas is investigated to identify the mechanism of cycle-to-cycle variations.
Highlights
Considering the limited fossil fuel resources and strict limitation of pollutant emissions, the Homogeneous Charge Compression Ignition (HCCI) engine is a promising technology as it combines advantages of both the diesel and spark ignition engines [1,2,3,4]
The experiments are performed at the Institute of Internal Combustion Engines, Karlsruhe Institute of Technology on a single-cylinder four-stroke Direct Injection (DI) gasoline engine (Fig. 1) with four canted valves, derived from a BMW F650 motorcycle manufactured by Rotax with several constructive modifications for numerous analyses
Extensions of the camshafts are provided with an angle encoder brand while the Top Dead Center (TDC) signal is set to the maximum valve lift
Summary
Considering the limited fossil fuel resources and strict limitation of pollutant emissions, the Homogeneous Charge Compression Ignition (HCCI) engine is a promising technology as it combines advantages of both the diesel and spark ignition engines [1,2,3,4]. In HCCI due to the highly diluted charge, high local peak temperatures are avoided, reducing the NOx formation [1,2,3,4]. Since high peak pressures and heat releases occur at high loads, the HCCI technology is applied for a limited range of load. To overcome this issue, strategies are developed to control HCCI combustion which refers to the Controlled Auto Ignition (CAI) concept [2, 3]. Exhaust Gas Recirculation (EGR) as a dilutant of the fresh fuel-air mixture is one of the strategies used for controlling HCCI combustion [1,2,3].
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