Cylinder Pressure Based Cylinder Charge Estimation in Diesel Engines with Dual Independent Variable Valve Timing
With stricter emission legislations and demands on low fuel
consumption, new engine technologies are continuously investigated.
At the same time the accuracy in the over all engine control and hence
also the estimation is tightened. Central for the internal combustion
control is the trapped cylinder charge and composition.
Traditionally cylinder charge is estimated using mean intake manifold
pressure and engine speed in a two dimensional look-up table. With the
introduction of variable valve timing, two additional degrees of
freedom are introduced that makes this approach very time consuming
and therefore expensive. Especially if the cam phasers are given large
enough authority to offer powerful thermal management possibilities.
The paper presents a semi-physical model for estimating in-cylinder
trapped mass and residual gas fraction utilizing cylinder pressure
measurements, and intake and exhaust valve lift profiles. The cylinder
pressure at intake and exhaust valve opening and closing together with
with manifold pressures and temperatures is combined with physical
models and a correlation for the heat transfer to determine the charge
temperature at intake valve closing required to calculate the trapped
mass trapped mass. The estimator is validated on test data from a
prototype engine with dual independent cam phasers under a wide range
of operating conditions, including large variations in valve timing
ranging from scavenging to early exhaust cam timing for thermal
The main contribution of this paper is the developed model's ability
to accurately estimate the trapped cylinder charge during large
independent variations in both intake and exhaust valve timing.
Andreas Thomasson, Sepideh Nikkar and Erik Höckerdal
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Last updated: 2021-11-10