Compression Ratio Estimation based on Cylinder Pressure Data
Four methods for compression ratio estimation based on cylinder
pressure traces are developed and evaluated for both simulated and
experimental cycles. The first three methods rely upon a model of
polytropic compression for the cylinder pressure. It is shown that
they give a good estimate of the compression ratio at low
compression ratios, although the estimates are biased. A method
based on a variable projection algorithm with a logarithmic norm of
the cylinder pressure yields the smallest confidence intervals and
shortest computational time for these three methods. This method is
recommended when computational time is an important issue. The
polytropic pressure model lacks information about heat transfer and
therefore the estimation bias increases with the compression ratio.
The fourth method includes heat transfer, crevice effects, and a
commonly used heat release model for firing cycles. This method is
able to estimate the compression ratio more accurately in terms of
bias and variance. The method is more computationally demanding and
is therefore recommended when estimation accuracy is the most
important property.
Marcus Klein, Lars Eriksson and Jan Åslund
Control Engineering Practice,
2006
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