Improving the predictiveness of the quasi-d combustion model for spark ignition engines with flexible intake systems |
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Authors: | T -K Lee Z S Filipi |
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Institution: | 1.Department of Mechanical Engineering,University of Michigan,Ann Arbor,USA |
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Abstract: | Fast and predictive simulation tools are prerequisites for pursuing simulation based engine control development. A particularly
attractive tradeoff between speed and fidelity is achieved with a co-simulation approach that marries a commercial gas dynamic
code WAVE™ with an in-house quasi-dimensional combustion model. Gas dynamics are critical for predicting the effect of wave
action in intake and exhaust systems, while the quasi-D turbulent flame entrainment model provides sensitivity to variations
of composition and turbulence in the cylinder. This paper proposes a calibration procedure for such a tool that maximizes
its range of validity and therefore achieves a fully predictive combustion model for the analysis of a high degree of freedom
(HDOF) engines. Inclusion of a charge motion control device in the intake runner presented a particular challenge, since anything
altering the flow upstream of the intake valve remains “invisible” to the zero-D turbulence model applied to the cylinder
control volume. The solution is based on the use of turbulence multiplier and scheduling of its value. Consequently, proposed
calibration procedure considers two scalar variables (dissipation constant C
β
and turbulence multiplier C
M
), and the refinements of flame front area maps to capture details of the spark-plug design, i.e. the actual distance between
the spark and the surface of the cylinder head. The procedure is demonstrated using an SI engine system with dual-independent
cam phasing and charge motion control valves (CMCV) in the intake runner. A limited number of iterations led to convergence,
thanks to a small number of adjustable constants. After calibrating constants at the reference operating point, the predictions
are validated for a range of engine speeds, loads and residual fractions. |
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Keywords: | |
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