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Monday, May 13th
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Tuesday May 14th / 13:30 – 15:00
Environment, Fuel and Combustion
Diesel Engines – Combustion Simulations
Room C
Strategies for switching between ECA and non ECA
operation for a medium-speed diesel engine with
EGR
Claude-Pascal Stoeber-Schmidt, TU Braunschweig, Germany
Peter Eilts, TU Braunschweig, Germany
The next stage of the IMO emission standards (Tier III) requires
the reduction of NOx emissions compared with current engine
designs from 2016 by 75% in coastal and designated areas. But
IMO Tier II limits continue to apply on the open sea. Against this
background, SCR and exhaust gas recirculation got into the focus
of marine engine designers. While the switching between the different
modes of operation with an SCR catalyst can be regulated
by a bypass, the switching is more difficult with an EGR concept.
Nevertheless, there is a desire to use the EGR technology in order
to avoid a further operating fluid and the large volume of an SCR
catalyst. The approach presented in this paper includes two-stage
turbocharging with an EGR turbocharger as additional EGR pump.
For switching between operating modes, all three charging units
need to be coordinated. Simple switching without any additional
control leads to extremely high-peak cylinder pressures above the
mechanical limit. Therefore additional switching control needs to
be provided to ensure safe engine operation and an optimal operating
range of the charging units. To ensure a good predictive quality
for the analysis a DI-jet-model for the prediction of the net heat
release rate which was further developed during the research work
is used. Furthermore, a refined approach for the estimation of nitrogen
dioxides, which uses empirical relations for the influence
of different operation parameters to estimate the nitrogen dioxide
emissions based on one baseline operation point, is used. In this
study possible strategies including higher variability for the charging
system, such as the use of a turbine bypass or variable turbine
geometry, and variable valve timing are analysed and compared
critically. However, current engine designs already have cam phasing
technologies to switch to low soot operation at low engine
load by delaying the inlet valve closing. These can also be used for
the switching between IMO Tier II and Tier III operation modes.
Therefore the necessity of a fully variable valve actuator and the
potential of a simple cam phasing are discussed. Furthermore, the
benefit of using variable turbine geometry in IMO Tier III operation
compared with a simple turbine bypass will be shown.
Potential investigation of PCCI combustion as NOx
reduction measure at low-load operation with low
CN LCO fuel
Hiroshi Tajima, Kyushu University, Japan
The IMO Tier III regulations require rigorous reduction of SOx as
well as PM and NOx. From 2015, LSFO (low sulphur fuel oil) required
in ECAs should decease its sulphur content to 0.1 mass %
of fuel, which is equal to one tenth of the present sulphur level
required of LSFO. The NOx emission rate [g/kWh] should be reduced
by as much as 75% from the present Tier II level from 2016.
Although various anti NOx pollution technologies, like EGR or
SCR have been ardently investigated, there exist three strong obstacles
to inhibit these technologies from practical use. The first
is that the sulphur content of the LSFO is still high enough to result
in metal corrosions in the EGR system by sulphuric acid and
in catalyst occlusion in the SCR system by ammonium hydrogen
sulphate after long-term use. The second is a wider load range required
for propulsion engines by the emission regulation in the
marine sector. It is difficult in general to adjust the exhaust clarifying
devices especially at low-load operations, since the enthalpy
of the exhaust gas is not sufficient to activate such devices. For
example, more EGR rate is necessary in lower-load conditions to
avoid severe combustion deterioration due to the lack of oxygen,
but this implies more power consumption of an EGR blower in
the system and the total thermal efficiency could be disastrous.
The third is the additional operational cost of the NOx reduction
systems. The EGR system needs a neutralising treatment system of
the sulphuric acid scrubbed down from the EGR gas and the SCR
system consumes urea or ammonia water according to the NOx
concentration in the exhaust pipes. Moreover, the LSFO would be
very expensive marine fuel as long as it is supplied with gas oil
classification of low sulphur content, so that other low-sulphur,
yet inexpensive components are desirable to burn in marine engines.
On the whole, a supplementary and economical anti NOx
pollution system is definitely wanted to cover the lower-load range
without fear of the cost increase in fuel consumption and device
operation. From the above point of view, PCCI (premixed charge
compression ignition), which has been studied in smaller onroad
fields for long time, could be a practical remedy for the first time
for the emissions from marine diesels. In this study, a new PCCI
combustion system is proposed to achieve drastic NOx reduction
for marine diesels. This system utilises a set of sprays from closely
aligned holes having injection directions intersecting one another
so as to cause mutual interaction and merger of the sprays by overlapping
injection periods and applying different injection rates. It
can enhance the mixture stratification suitable for the PCCI combustion.
As for the cheaper substitute of the low-sulphur gas oil,
neat LCO (light cycle oil) was also firstly introduced as a potential
LSFO in this study. LCO is composed from distillate components
produced in a FCC (fluid catalytic cracking) process in modern oil
refinery plants and it has sometimes notoriety for its poor ignitability
thanks to its high aromaticity. LCO was casted in a new
light here by utilising its good valorousness and its long ignition
delay for the PCCI combustion. Lower-load operation also
favours the PCCI concept because the abnormal combustion of
the PCCI mode usually happens at higher-load conditions. The
durability against the pre-ignition of LCO was greatly enhanced by
water emulsification. The potential of the strategy was examined
through observation of the spray merging and combustion process
in a rapid compression expansion machine. All in all, the ignition
control of PCCI combustion in large engines was successfully realised
for the first time.
Partially premixed combustion (PPC) for low-load
conditions in a marine engine using computational
and experimental technique
Kendra Shrestha, Aalto University of Technology, Finland
Ossi Kaario, Aalto University of Technology, Finland
Martti Larmi, Aalto University of Technology, Finland
Teemu Sarjovaara, Aalto University of Technology, Finland
Matteo Imperato, Aalto University of Technology, Finland
The diesel engine has been the most powerful and relevant source
of power in the automobile industries from decades due to its excellent
performance, efficiency and power. On contrary, there are
numerous environmental issues of the diesel engines hampering
the environment for which it has been a great challenge for the
researchers and scientists. In the recent years, numerous strategies
have been introduced to eradicate the emission of the diesel engines.
Among them, partially premixed combustion (PPC) is one
of the most emerging and reliable strategy. PPC is a compression
May 2013 | Schiff&Hafen | Ship&Offshore SPECIAL 35