CIMAC Congress - Schiff & Hafen

CIMAC CONGRESS | BERGEN 2010
Japan because of the higher butane content in Japanese manufactured
gas, which can reach to as high as 3%. The autoignition mechanism
in these large-sized gas engines should be clarified in order to inhibit
knocking development and to achieve higher thermal efficiency.
Unfortunately, knocking observation is awfully difficult especially in
large engines since the high and impactive in-cylinder pressure limits
the size of glass windows and thus restricts the viewing field into the
end-gas region. In this study, a RCEM (Rapid compression and
expansion machine) was introduced to realize both the in-cylinder
conditions compatible with actual gas engines and the full transversal
access into the combustion chamber by utilizing a reservoir tank of
compressed and preheated air. This RCEM was firstly motored with
its intake valve closed. After it reached to its rating speed, the intake
valve was activated only once synchronously with its piston motion
to simulate the intake stroke of a real engine. The pre-compression
and preheating of the intake air allowed lower geometric compression
ratio, which enabled its clearance volume to be a square block of an
opposed pair of transparent windows. The dimensions of the
windows are 200mm in width and 50mm in height, whereas the
compression pressure and maximum combustion pressure exceeded
10 MPa and 20 MPa respectively. Visualization results revealed the
autoignition phenomena in large-sized gas engine for the first time.
Tiny cores of autoignition were clearly captured to scatter around the
whole combustion chamber over a certain range of intake
temperatures. The boundaries dividing heavy knocking, mild
autoignition like HCCI combustion, and premixed flame propagation
initiated by pilot diesel flame were examined in detail through
changing the experimental conditions precisely. KIVA 3V code
coupled with CHEMKIN II package was also applied to examine the
effect of Butane content in manufactured gas since Butane has the
smallest octane index in the manufactured gas components and it is
one of the smallest hydrocarbons that show the negative temperature
gradient, which effect on ignition delay is difficult to simulate the
effect on ignition delay. The simulations were carried out for both the
RCFM and Mitsui 6MD20G engine. The results showed that 3D CFD
with detailed chemical kinetics successfully reproduce the onset of
knocking in the actual gas engine and it could be useful to predict the
effect of some engine parameters like EGR rate to avoid knocking or
abnormal combustion.
10:30 June 15th Room Klokkeklang
(9–2) Turbochargers & Turbomachinery –
Advanced Turbocharging Systems
IMO III emission regulation: Impact on the
turbocharging system
E. Codan, S. Bernasconi, H. Born, ABB Turbo Systems
Ltd., Switzerland
In combination with advanced turbocharging, a number of internal
engine measures have been considered for fulfilling the IMO Tier II,
the second stage of the IMO’s regulations on exhaust emissions from
marine engines. Coming into force at the beginning of 2011, IMO
Tier II requires a reduction in emissions of oxides of nitrogen (NOx)
of 20% compared to IMO Tier I. In order to fulfil the requirement of
the IMO Tier III stage coming into force in 2016, a major decrease in
specific NOx emissions (about -80% compared to the IMO Tier I
values) needs to be achieved in designated Emission Control Areas
(ECAs). Emissions of oxides of sulphur (SOx) and particulate matter
(PM) are to be controlled by limiting the sulphur content of the fuel
used. An alternative measure is the use of SOx abatement equipment
such as sea water scrubbers, fresh water scrubbers or a dry exhaust gas
cleaning system. For IMO Tier III either external measures
(aftertreatment technologies) or a combination of internal engine
technologies are required. This paper provides an overview of IMO
Tier III solutions with regard to NOx reduction measures and their
impact on the engine turbocharger system, taking into account both,
single stage and 2-stage turbocharging. From a range of possible
solutions, two NOx reduction technologies with high potential, SCR
and EGR, have been selected for study in greater detail. Selective
Catalytic Reduction (SCR) is a proven technology that basically allows
any engine to fulfil IMO Tier III. Nevertheless some configurations
require SCR to be installed before the turbine (two-stroke engines,
two-stage turbocharging), which affects transient operation. The
impact on the system and an evaluation of several countermeasures
are detailed based on transient simulations. Exhaust Gas Recirculation
(EGR) is an established NOx-reduction technology in the automotive
sector but is not yet state-of-the art for large engines. An evaluation of
several strategies with regard to NOx reduction, fuel consumption,
and other relevant parameters demonstrate the potential and the
advantages of recirculating exhaust gases. A further challenge for the
turbocharging system is the necessity to provide the variability needed
to allows an engine to fulfil the low emission limits within the ECA’s
while running with the highest fuel economy elsewhere.
Utilisation of cylinder air injection as a low
load and load acceptance improver on a
medium-speed diesel engine
C. Wik, S. Hostman, Wärtsilä Finland Oy, Finland
Development of engine concepts for lower NOx emissions e.g. by
means of Miller valve timing (early inlet valve closure) makes
loading capability worse, especially at low loads. Continuous
increase of cylinder output makes the situation even worse; larger
absolute load steps, as kW or bar BMEP, and larger turbochargers
mean longer rotor acceleration and slower pressure increase.
Furthermore, Miller timings demand higher charge air pressure, i.e.
the pressure ratio capacity of the turbocharger must be greater. This
causes the optimum efficiency of turbocharger to move towards
higher pressure and decreased efficiency at low load which results in
poor load response at low load. Future engine concepts will probably
also include a shorter valve overlap (scavenge period), which also
deteriorates low load performance. Poor load response is directly
linked to high smoke and particle emissions. All this sums up in the
fact that low load operation of state-of-art medium speed diesel
engines is known to result in fairly high smoke emissions and
thermal loads. This is a problem in transient operation and especially
for auxiliary engines that need to be fast reacting generating sets.
There are different means available to compensate for the transient
problems, of which, air injection in different ways before the
combustion starts is one. Air could be injected directly on the
turbocharger compressor; so called air jet assist or into the air
receiver. Both these methods, however, always give a certain time
delay in load response situation, and the air receiver injection may
also force the turbocharger to stall. There is one additional method
that has potential in bringing large benefits compared to the
available methods mentioned above and this is injection of
pressurized air directly into the cylinders. In this paper, focus will be
put on air injection into the air receiver or into the cylinders.
Preliminary transient and stationary tests aimed for proving the
potential on a medium speed diesel engine have been performed
utilising the existing starting air valves. These tests resulted in
considerable reduction of smoke opacity during engine start-up as
well as ability to run 2-step load application fulfilling classification
criteria. Final outcome of the tests will be presented in the paper.
Design of a production system for an auxiliary engine, with its
challenges, will be presented together with rig test results for system
optimisation, verification, and validation. Ultimate engine test
results, proving the concept, will finally be reported upon availability.
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Ship & Offshore | 2010 | No. 3