46 4 Real Working-Process Analysis
on very complex engines (DI-engines, diesel engines and also HCCI engines) can be performed
by continuous increasing of result accuracy.
A powerful and important capability of the real working-process analysis is represented by the
possibility to extend the modeling and analyses from the engine processes directly involved in
the conservation equations (mass and energy balance) to other ones of interest, like exhaust gas
emissions (NO
X
, UHC, soot, etc.), knocking, mixture ignition, etc., that are today mandatory for
a successful engine development process.
The real working-process analysis in combination with the 1D-CFD-simulation (“internal
coupling” between WP and 1D-CFD) allows to extend the analysis from the combustion
chamber as an open thermodynamic system to the whole engine, where the flow in the exhaust
and intake system, respectively, can be properly one-dimensionally investigated up to a certain
design complexity. Here the “internal coupling WP-1D-CFD” permits to increase the
predictability of these simulation tools at least regarding the exchange process. Modern quasi-
dimensional combustion models introduce, for any kind of engine, also a promising
predictability in the calculation of the heat release based on a “coarse” analysis of the fluid
motion within the combustion chamber. From a global point of view, these tools are getting more
and more relevant and decisive in supporting the development of today’s and future engines,
respectively, where the number of parameters that can be varied has been and will be
continuously increasing.
The following points are a selection of the main investigation topics using the real working-
process analysis:
x
Analysis of the engine operating cycle in all relevant thermodynamic terms (piston work,
variation of internal energy, fuel heat-release, wall heat-transfer, direct fuel-injection and
enthalpy fluxes through the valves) using pressure trace signals or combustion profiles
x
Volumetric efficiency and residual gas calculation at IVC
x
Starting from an accurate calibration of the models, modern real working-process
analyses are able to ensure a good predictability by varying valve timings and injection
strategies within a certain range of variation
x
Extension to non-thermodynamic relevant models for the prediction of, e.g., exhaust gas
emissions and knocking effects.
The limitations of the real working-process analysis have to be found mainly in the capability to
analyze the influence of design details (e.g. a slight changing design of the piston surface or of
the intake channel) on the fluid motion and all other processes connected, or generally in all