Browse Publications Technical Papers 2019-01-0469
2019-04-02

Predictive Two Zone SI Combustion Model for Real-Time 1-D Gas Code 2019-01-0469

The automotive industry is facing increasing environmental, legal & liability requirements imposed by the World-harmonized Light-duty Vehicles Test Cycle (WLTC) together with the Real Driving Emissions (RDE) legislation emission limits. Moreover, future electrified / hybridized vehicle powertrains require a significant increase in the complexity of powertrain architecture and engine calibration. The mean value engine models do not provide sufficient accuracy when operating outside of validated regions and during transient conditions. Moreover, their development time and cost is very high, given that they are applicable to only one specific engine variant. On the other hand, predictive and accurate 1-D gas models are typically 50-100 times slower compared to real-time. On top of that, combustion is typically modelled with a multi-component Wiebe model obtained from in-cylinder heat release analysis. This paper overcomes these problems using a newly developed predictive model of spark ignited (SI) combustion implemented within a faster-than-real-time 1-D gas dynamics simulation tool 'WAVE-RT' running at a resolution of one degree in crank angle. In this new model, the combustion chamber is divided into two zones (burned and unburned), separated by a thin flame front. Each zone is considered to be in thermodynamic equilibrium. The flame front is assumed to be an expanding sphere whose surface is wrinkled by turbulence and that progressively intersects the combustion chamber walls. The flame front advances at turbulent speed. The flame front speed depends on an empirical formula for laminar flame speed, and fractal turbulent flame model. The former determines response of the model to trapped air to fuel ratio, EGR, in-cylinder pressure, and temperature. The latter is based on a predictive K-k turbulence model and determines the degree of wrinkling of the flame front. An automotive turbocharged direct injection gasoline engine is modeled and validated within the real-time 1-D gas dynamics code over a complete engine operating range. The predictive SI combustion model is set up and fitted to heat release analysis data that are based on in-cylinder pressure measurements. At the end of validation process, the combustion model is given by a set of universal constants valid over the whole engine operating range.

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