Heat Transfer
in the SI/HCCI Engine
Abstract:
Experimental studies are carried out to provide qualitative
and quantitative insight into gas to wall heat transfer in gasoline
fueled Spark Ignition (SI) and Homogeneous Charge Compression
Ignition (HCCI) engines. Fast response thermocouples are embedded
in the piston top and cylinder head surface to measure instantaneous
wall temperature and heat flux. Heat flux measurements are then
used to assess several heat transfer correlations, in order
to refine and validate mathematical models.
Background:
The Homogeneous Charge Compression Ignition (HCCI) is currently
under widespread investigation, due to its potential to increase
thermal efficiency while greatly decreasing harmful
exhaust pollutants.
Auto-ignition
and combustion rates in a Homogeneous Charge Compression Ignition
(HCCI) engine are very closely coupled to the heat transfer
phenomena. Hence, a thorough understanding of the heat transfer
process is critical for extending the load range and managing
thermal transients. An improved heat transfer model, valid for
a range of HCCI conditions, is an essential element in the development
of predictive thermo-kinetic simulations.
The fuel,
air and residual gas are generally expected to be well mixed
in an HCCI engine and its combustion is often described as controlled
auto-ignition. The combustion process starts at multiple locations
and is governed by chemical kinetic rather than turbulent flame
front propagation, as in Spark Ignition (SI) engines, or a stratified
diffusion flame, as in conventional highly stratified Compression
Ignition (CI) engines. Hence, turbulence and mixing rates have
a much smaller effect on HCCI combustion, while in-cylinder
thermal conditions have a critical impact on HCCI ignition timing
and burning rate. The thermal condition of the combustion chamber
is closely tied to heat transfer from the hot gas to the walls.
Thus, good understanding of the heat transfer process in the
combustion chamber is prerequisite for developing HCCI engine
control strategies and thermal management schemes.
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Crank/Piston Instrumentation
Researchers:
Junseok Chang,
Orgun Güralp,
Mark Hoffman
Zoran Filipi,
Dennis Assanis
Sponsors:
General Motors
Goals:
The goal of this work is to experimentally quantify the effect
of various operating parameters on in-cylinder heat transfer and
HCCI combustion. It is important to understand the sensitivity
of chamber thermal conditions on HCCI performance and emissions
and the details behind HCCI specific heat transfer phenomena.
This will help to allow more effective means to more precisely
control HCCI combustion and to explore the limits of its range
of operability. Additionally, experimental results can be used
to improve heat transfer model for HCCI engine simulation and
support control strategy. The main technique behind accomplishing
this is through the use of fast response piston and head surface
thermocouples which are used to accurately quantify wall temperatures
and heat flux.
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