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Technical Paper

Towards Control-Oriented Modeling of Natural Gas-Diesel RCCI Combustion

2015-04-14
2015-01-1745
For natural gas (NG)-diesel RCCI, a multi-zonal, detailed chemistry modeling approach is presented. This dual fuel combustion process requires further understanding of the ignition and combustion processes to maximize thermal efficiency and minimize (partially) unburned fuel emissions. The introduction of two fuels with different physical and chemical properties makes the combustion process complicated and challenging to model. In this study, a multi-zone approach is applied to NG-diesel RCCI combustion in a heavy-duty engine. Auto-ignition chemistry is believed to be the key process in RCCI. Starting from a multi-zone model that can describe auto-ignition dominated processes, such as HCCI and PCCI, this model is adapted by including reaction mechanisms for natural gas and NOx and by improving the in-cylinder pressure prediction. The model is validated using NG-diesel RCCI measurements that are performed on a 6 cylinder heavy-duty engine.
Technical Paper

Modeling of Conventional and Early Diesel Injection Combustion Characteristics using FGM Approach

2013-04-08
2013-01-1108
The wide range of diesel engine operating conditions demand for a robust combustion model to account for inherent changes. In this work, the Flamelet Generate Manifold (FGM) approach is applied, in STAR-CD framework, to simulate the conventional injection- and early injection-timing (PCCI like) combustion regimes. Igniting Counter flow Diffusion Flamelets (ICDFs) and Homogeneous Reactors (HRs) are used to tabulate chemistry for conventional and PCCI combustion modes, respectively. The validation of the models with experimental data shows that the above consideration of chemistry tabulation results in accurate ignition delay predictions. The study reveals that a moderate amount of 5 different pressure levels is necessary to include in the FGM database to capture the ignition delay in both combustion regimes.
Technical Paper

Modeling Fuel Spray Auto-ignition using the FGM Approach: Effect of Tabulation Method

2012-04-16
2012-01-0157
The Flamelet Generated Manifold (FGM) method is a promising technique in engine combustion modeling to include tabulated chemistry. Different methodologies can be used for the generation of the manifold. Two approaches, based on igniting counterflow diffusion flamelets (ICDF) and homogeneous reactors (HR) are implemented and compared with Engine Combustion Network (ECN) experimental database for the baseline n-heptane case. Before analyzing the combustion results, the spray model is optimized after performing a sensitivity study with respect to turbulence models, cell sizes and time steps. The standard High Reynolds (Re) k-ε model leads to the best match of all turbulence models with the experimental data. For the convergence of the mixture fraction field an appropriate cell size is found to be smaller than that for an adequate spray penetration length which appears to be less influenced by the cell size.
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