Utilizing Cylinder Pressure Data for Compression Ratio Estimation
Four methods for compression ratio estimation based on cylinder
pressure traces are developed and evaluated for simulated and
experimental cycles. Three methods rely upon a model of polytropic
compression for the cylinder pressure. It is shown that they give
good estimates with a small bias at low compression ratios. 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 compression ratio. The
fourth method includes heat transfer, crevice effects, and a
commonly used heat release model for firing cycles. This method
estimates the compression ratio more accurately in terms of bias and
variance. The method is more computationally demanding and thus
recommended when estimation accuracy is the most important property.
In order to estimate the compression ratio as accurately as
possible, motored cycles with high initial pressure should be used.
Marcus Klein and Lars Eriksson
IFAC World Congress,
2005

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