CIMAC Congress - Schiff & Hafen

Monday, 14 June
Tuesday, 15 June
of around spray, and the fl ame at downstream region spreads in case
of burning with high water contents emulsifi ed fuel.
(3) In the high ambient temperature, the ignition lag became
short regardless of water contents in emulsifi ed fuels, and the
burning periods became long.
(4) As the water contents increased, the ignition lag became short
whereas the burning period became short.
(5) In the high ambient pressure, the ignition lag became short
regardless of water contents. In the high-temperature and highpressure
combustion chamber same as in high load diesel engine
conditions , the differences of ignition lag between the emulsifi ed
fuel and MDF become little, and the burning period of emulsifi ed
fuel becomes short in compared with MDF. From these experimental
results using emulsifi ed fuels, it is presumed that the combustion
temperature decreases by evaporating latent heat of water, the
burning period becomes short, the high temperature burning period
decreases, and then, the creation of thermal NO is suppressed for
them.
Assessing the performance of spray and
combustion simulation tools against
reference data obtained in a spray
combustion chamber representative of
large two-stroke diesel engine combustion
systems
R. Schulz, K. Herrmann, G. Weisser, B. v. Rotz, S.
Hensel, F. Seling, Wärtsilä Switzerland Ltd,
Switzerland,
Y. M. Wright, M. Bolla, K. Boulouchos, Swiss Federal
Institute of Technology (ETH) Zürich, Switzerland
The optimization of the combustion systems of large marine diesel
engines still relies largely on extensive testing; however, it is more
and more supported by computational fl uid dynamics (CFD)
simulations – in spite of limitations regarding the applicability of
the available spray, evaporation, combustion and emissions
formation models to those systems. As combustion is particularly
sensitive to the fuel vapour distribution, the accurate simulation of
spray and evaporation processes is seen as a prerequisite for reliable
combustion and emissions formation results. In order to enable the
validation of such simulations at conditions relevant to large twostroke
engines, a novel experimental setup was realized, consisting
of an optically accessible, disk-shaped constant volume chamber of
500 mm diameter with peripheral injection into a swirling fl ow. In
this setup, thermo- and fl uid dynamic conditions similar to those
applying at start of injection of an engine are obtained by feeding
pressurized and heated air or nitrogen to the spray combustion
chamber (SCC) via inclined intake ports. The SCC has been used
extensively for visualizing spray phenomena by means of shadow
imaging techniques, thereby covering a large range of operating
conditions, including non-reactive and reactive cases, as well as a
variety of confi gurations, specifi cally with respect to the injector
nozzle. In the present paper, those data are used for the validation of
different CFD sub-models for spray and evaporation, based on
initial conditions at start of injection, which have been derived on
the basis of comprehensive simulations of the fi lling of the chamber,
verifi ed separately through fl ow measurements. Additionally, since
each spray is also affected by the conditions upstream the orifi ce, the
fl ow inside the injector is simulated in order to identify its effect on
the injection boundary conditions, thereby taking into account the
geometry of the nozzle tip actually used in the SCC tests, which is
determined by means of computer tomography. This investigation
hence focuses on the key aspects of spray and evaporation simulation,
including different fuel modelling approaches and injector geometry
Wednesday, 16 June
Thursday, 17 June
effects. It allows identifying the most suitable models and model
combinations, thereby establishing a basis for the simulation of
combustion and emissions formation, and thus represents a major
step towards the application of CFD for actual combustion system
optimization.
Modelling of the oxidation of fuel sulphur
in low speed two-stroke diesel engines
A. Andreasen, S. Mayer, MAN Diesel & Turbo SE,
Denmark
In large marine two stroke diesel engines during combustion of
sulfur containing fuel, the sulfur is oxidised to SO 2 , mainly, although
substantial amounts of SO 3 and H 2 SO 4 will form as well. These
latter species may cause corrosional wear of the cylinder liner if not
neutralised by lube oil additives. Potential attacks is due to either
condensation of sulfuric acid on the cylinder liner lube oil fi lm or
direct dissolution of oxidised sulfur species in the lube oil fi lm in
which reaction with dissolved water may be the source of acidic
species. In order to evaluate and predict corrosional wear of the liner
material, it is pivotal to have realistic estimates of the distribution/
concentration of oxidised sulfur species as well as a reliable model
of formation, transport and destruction of acidic species in the oil
fi lm. This paper addresses the former part by invoking a detailed
reaction mechanism in order to simulate the oxidation of fuel
bound sulfur and predicting the concentration of SO 2 as well as the
conversion fraction into SO 3 and H 2 SO 4 . The reaction mechanism is
coupled to a realistic model of the combustion process in which the
air entrainment into the combustion zone is accounted for. The
results of the simulation are evaluated with respect to previously
applied models as well as existing data on the conversion fraction of
SO 2 to SO 3 and H 2 SO 4 . The conversion fraction is found to be in a
range of 2.6-6.7 %.
A study on the spray combustion
characteristics of bio diesel fuel
A. Azetsu, K.-O. Hagio, M. Aoki, Tokai University,
Japan
Bio-derived fuel, such as vegetable oil and so forth, is a renewable
energy and obtained a considerable amount of interests as a
promising alternative fuel for IC engines. Concerning the
alternative fuel for diesel engine, fatty acid methyl ester, FAME, is
now in the stage of practical usage. The production of FAME is
examined from many vegetable oils such as palm oil, rapeseed
oil, coconuts oil, etc., and there are many studies concerning the
applicability of FAMEs as an alternative fuels for diesel engines.
However majority of those studies are engine tests to examine the
effect on engine performance and emission characteristics, and
the study concerning the fundamental characteristics of spray
combustion, i.e., ignition delay, fl ame temperature and soot
production characteristics are still needed. From these
backgrounds, the objective of our study is to understand the
fundamental spray combustion characteristics of FAME mixed
with diesel oil, called Bio Diesel Fuel hereafter. To examine the
phenomena in detail, diesel spray fl ame formed in the constant
volume high pressure vessel was visualized and the fl ame
temperature and the soot concentration were analyzed by two
color method of luminous fl ame. The ambient high-pressure and
high-temperature conditions inside the constant volume vessel
were achieved by the combustion of hydrogen in an enriched
oxygen and air mixture. The composition of the mixture was such
that the oxygen concentration after hydrogen combustion was
approximately 21% by volume. Following hydrogen combustion,
No. 3 | 2010 | Ship & Offshore
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