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|Title: ||A study of controlled auto ignition (CAI) combustion in internal combustion engines|
|Authors: ||Milovanovic, Nesa|
Heat release rate
Internal exhaust gas recirculation
Gas exchange process
Variable valve timings
|Issue Date: ||2003|
|Publisher: ||© Nebojsa Milovanovic|
|Abstract: ||Controlled Auto Ignition (CAI) combustion is a new combustion principle in internal
combustion engines which has in recent years attracted increased attention. In CAI
combustion, which combines features of spark ignition (SI) and compression ignition
(CI) principles, air/fuel mixture is premixed, as in SI combustion and auto-ignited
by piston compression as in CI combustion. Ignition is provided in multiple points,
and thus the charge gives a simultaneous energy release. This results in uniform
and simultaneous auto-ignition and chemical reaction throughout the whole charge
without flame propagation. CAI combustion is controlled by the chemical kinetics
of air/fuel mixture with no influence of turbulence.
The CAI engine offers benefits in comparison to spark ignited and compression
ignited engines in higher efficiency due to elimination of throttling losses at part
and idle loads. There is a possibility to use high compression ratios since it is not
knock limited, and in significant lower NOx emission (≈90%) and particle matter
emission (≈50%), due to much lower combustion temperature and elimination of
fuel rich zones.
However, there are several disadvantages of the CAI engine that limits its practical
application, such as high level of hydrocarbon and carbon monoxide emissions, high
peak pressures, high rates of heat release, reduced power per displacement and
difficulties in starting and controlling the engine.
Controlling the operation over a wide range of loads and speeds is probably the major
difficulty facing CAI engines. Controlling is actually two-components as it consists
of auto-ignition phasing and controlling the rates of heat release. As CAI combustion
is controlled by chemical kinetics of air/fuel mixture, the auto-ignition timing
and heat release rate are determined by the charge properties such as temperature,
composition and pressure. Therefore, changes in engine operational parameters or in
types of fuel, results in changing of the charge properties. Hence, the auto-ignition
timing and the rate of heat release.
The Thesis investigates a controlled auto-ignition (CAI) combustion in internal combustion
engines suitable for transport applications. The CAI engine environment is
simulated by using a single-zone, homogeneous reactor model with a time variable
volume according to the slider-crank relationship. The model uses detailed chemical
kinetics and distributed heat transfer losses according to Woschini's correlation .
The fundamentals of chemical kinetics, and their relationship with combustion related
problems are presented. The phenomenology and principles of auto-ignition
process itself and its characteristics in CAI combustion are explained. The simulation
model for representing CAI engine environment is established and calibrated
with respect to the experimental data. The influences of fuel composition on the
auto-ignition timing and the rate of heat release in a CAI engine are investigated.
The effects of engine parameters on CAI combustion in different engine concepts
fuelled with various fuels are analysed. The effects of internal gas recirculation
(IEGR) in controlling the auto-ignition timing and the heat release rate in a CAI
engine fuelled with different fuels are investigated. The effects of variable valve
timings strategy on gas exchange process in CAI engine fuelled with commercial
gasoline (95RON) are analysed.|
|Description: ||A Doctoral Thesis. Submitted in partial fulfilment of the requirements for the award of Doctor of Philosophy of Loughborough University.|
|Appears in Collections:||PhD Theses (Aeronautical and Automotive Engineering) |
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