Effect of Combustion Models on Prediction of Cylinder Pressure Ringing in a DI Diesel Engine

Paper #:
  • 2018-01-0194

Published:
  • 2018-04-03
Abstract:
Pressure ringing in internal combustion engine is observed in in-cylinder pressure measurement, which may be due to combustion dynamics, pressure oscillation inside the combustion chamber, and inside a recessed drilled hole for cylinder pressure sensor installation. In the present study, combustion process of a production diesel engine instrumented with pressure sensors in the cylinder head was analyzed using 3D CFD software CONVERGE. The engine utilized in this analysis is a 2-valve 4.5L 4-cylinder heavy-duty direct-injection diesel engine for off-road applications. Various combustion models such as Shell/CTC ignition-combustion model, SAGE model with n-Heptane mechanism of Chalmers University, and ECFM-3Z model were employed to review their capability in capturing pressure ringing phenomena. The raw pressure signal from measurement and simulation was analyzed by FFT. It was found that the Shell/CTC model does not reproduce the pressure oscillation observed in the experiment, while SAGE and ECFM-3Z combustion models well capture the primary resonance frequency of probe hole. Visible pressure oscillation in the combustion chamber starts at the early premixed combustion stage around TDC. The heat release rate clearly shows a spike at this moment, which is responding to the auto-ignition event. The SAGE model successfully captures the Negative Temperature Coefficient (NTC) effect on pressure ringing during the premixed combustion stage but the Shell/CTC model cannot. The NTC usually occurs at cylinder gas temperature around 900 K, which is close to the engine condition before ignition. Due to detailed elementary reactions relating to the low temperature combustion included in the present reaction mechanism, the SAGE model reproduces the detailed chemical kinetics during this premixed combustion stage. The Shell/CTC model is over-simplified regarding to this aspect. Parametric studies were also conducted to investigate the effect of the drilled hole length on pressure measurement. The results showed that the shorter hole length produces the higher resonance frequency that can be easily distinguished by the resonance frequency of combustion chamber.
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