Trends and Limits of Two-Stage Boosting Systems for Automotive ...

Section 1.4 Chapter 1
� Synthesis of the different interactions between the engine, EGR systems
and boosting architectures.
1.4 Methodology
The correct definition of an appropriate methodology is essential to reach
the objectives that have been set out for this thesis.
As every research work, the first step when subject boundaries have been
defined is to perform an exhaustive literature review to assess the state of the
art. Being the present work a synthesis of boosting systems, the review has
been extended to all existing solutions: two-stage turbocharging systems, mechanical
superchargers, electric boosting systems, compressor performance enhancement
systems, turbocompounding. . . These solutions have been already
applied on a wide range of applications and engine swept volumes for both
reducing fuel consumption and increasing rated power. An analysis and synthesis
of these results is thus an important starting point to understand the
potential of advanced boosting systems and to select the most efficient architectures
for the specific case of downsized-downspeeded Diesel engines. The
results of this synthesis will be exposed in chapter 2 and only the selected
architectures will be further analyzed in the frame of this work.
The complexity of multistage charging system is not only inherent in the
number of elements and parameters but also in the interactions that exist between
the different systems. To characterize the main factors that affect as the
engine as the boosting architecture performance, a theoretical study is performed
in chapter 3 with the development of an analytical model. By keeping
an analytical solution, this approach is particularly interesting to check the influence
of different variables independently and to understand their particular
contribution to the energy balance. This model is only conceptual and cannot
be applied for matching calculations. But it constitutes a first step in the
behavior comprehension of complex two-stage architectures before developing
more sophisticated models in the following chapters of the thesis.
As already mentioned in the motivations section, trying to reach experimentally
the general objective of the thesis would results very expensive and
few effective. That is why most of the work will be carried out by simulations.
To be confident of the results obtained and to reduce as much as possible
12