Browse Publications Technical Papers 2018-01-0189
2018-04-03

Analysis of Thermal Stratification Effects in HCCI Engines Using Large Eddy Simulations and Detailed Chemical Kinetics 2018-01-0189

The operating range of Homogeneous Charge Compression Ignition (HCCI) engines is limited to low and medium loads by high heat release rates. Negative Valve Overlap (NVO) can be used to facilitate ignition of high octane number fuels and control pressure rise rates by diluting the mixture with hot residual gas and introducing some thermal stratification. Controlling the thermal stratification results in sequential autoignition, reduced heat release rates, and operating range extension. Therefore, fundamental understanding of thermal stratification in HCCI combustion with high levels of internal residuals is necessary, along with the development of appropriate models to simulate thermal stratification and its effects on HCCI combustion.
A 3-D Computational Fluid Dynamics (CFD) model of a 2.0 L GM Ecotec engine (LNF type) engine cylinder, modified for HCCI combustion, was developed using CONVERGE CFD. Large Eddy Simulations (LES) were combined with combustion modeling using detailed chemical kinetics. Fifteen consecutive cycles were simulated and the results were validated against individual cycle data of 300 consecutive experimental cycles. The results showed a competing effect between mixing of fresh charge and residuals, and heat transfer-induced thermal stratification during the compression stroke. A large amount of thermal stratification was found at the onset of autoignition, resulting in a skewed temperature distribution. Compositional stratification was minimal despite the large residual gas fraction. Thermal stratification resulted in sequential autoignition, with the hotter regions igniting earlier. Significant spatial variability of thermal stratification on a cyclic basis was found, which did not affect the bulk thermal stratification. Heat release was found to depend predominantly on the bulk thermal stratification rather than the spatial distribution of thermal stratification.

SAE MOBILUS

Subscribers can view annotate, and download all of SAE's content. Learn More »

Access SAE MOBILUS »

Members save up to 18% off list price.
Login to see discount.
Special Offer: Download multiple Technical Papers each year? TechSelect is a cost-effective subscription option to select and download 12-100 full-text Technical Papers per year. Find more information here.
We also recommend:
JOURNAL ARTICLE

A Study of Piston Geometry Effects on Late-Stage Combustion in a Light-Duty Optical Diesel Engine Using Combustion Image Velocimetry

2018-01-0230

View Details

TECHNICAL PAPER

Optimal Peak Pressure and Exhaust Temperature Tracking Control for a Two-Zone HCCI Engine Model with Mean Burn Duration

2009-01-1130

View Details

TECHNICAL PAPER

Development Of Fugine Based on Supermulti-Jets Colliding with Pulse: Leading to Stable Plug-Less Start and Improvement of HCCI with Satisfactory Strength of Structure

2014-01-2639

View Details

X