Bergen C25:33 -- a New Rolls-Royce Medium Speed Engine

    LONDON, July 13 An Intensive Three Year Development
Programme Has Produced a Versatile and Compact New 250mm Bore, 900-1000rpm
Engine, the Bergen C25:33.
    Suited to 50Hz or 60Hz power generation applications on land, and both
propulsion and auxiliary applications at sea, the engine is initially
available with 5,6,8 or 9 cylinders in line spanning a power range from 1,200
to 2,700kW.  It can utilise a wide spectrum of liquid fuels, including
distillates, heavy fuel and crude. V-formation versions of greater power, up
to 6 MW, are under development, as are gas engines founded on the same design.
    Rotational speed was centred around 900-1000rpm as the best compromise
between the preference in some areas of the industry for a low speed engine
and the potentially lower price per kW of a fast-turning unit.  An evaluation
of available materials and the desired time between overhauls determined both
the piston speed (and thus the stroke) and the brake mean effective pressure.
However, if the customer requires, the C-engine can also be delivered for
720/750 rpm operation.
    The initial decision to design a new engine to take over from the mature
K-series was made in 1997, and at an early stage of the project an agreement
was signed with Hyundai Heavy Industries of Korea to develop the product as a
combined effort.  Starting in 1998, concepts were evaluated and the market-
driven design was produced, enlisting the help of the latest design tools and
the services of specialist consultants.  Two six cylinder technology
development engines were built and extensively tested, one at Bergen and one
at Hyundai, with each partner manufacturing specific groups of components.

    The result of weighing the various factors is an engine with the following
parameters:

    Bore:                                  250mm
    Stroke:                                330mm
    Cylinder volume:                       16.2 litres
    Speed range:                           720-1000rpm
    Output:                                220 - 300 kW/cyl
    BMEP:                                  22.6 - 24.7 bar
    Specific fuel cons:                    182 - 186 g/kWh
    (to ISO at IMO NOx)
    Mean piston speed:                     7.9  - 11 m/s
    Firing pressure:                       190 bar
    Cylinders:                             5,6,8,9 in line
                                       (V-engine versions to follow)
    Power range:                           1,200-2,700kW

    The core design requirements for the Bergen C25:33 engine from Rolls-Royce
were:
    -- Reliability and durability
    -- High availability, through long service intervals and simple servicing
    -- Compactness, optimum power for perceived applications, rational and
        cost-effective production
    -- Economy of operation - with low fuel lube-oil and spares consumption,
        and also environmentally friendly
    -- Ease of installation, operation and maintenance
    -- Electronic control and monitoring to facilitate condition-based
        maintenance.

    The C-engine has been designed around the philosophy that a new design
must be cost-effective from the outset but should in the longer term be able
to profit from general improvements in materials and component design for
further upratings.
    Medium speed diesel engines typically have a long production life and
begin with large growth margins.  Such an approach may lead to engines that
are unnecessarily large and expensive.  The C-engine has been designed with
sufficient margins, and upratings will come through real improvements in
existing parts and measurable technical progress.
    A major attraction of the C25:33 for the customer is the long time between
overhauls, irrespective of whether the engine runs on HFO or distillates.
Times between overhauls are set at 15,000 hours for the top end and 30,000
hours for the bottom end on HFO, and 20,000/40,000 hours on MDO, respectively.
Routine servicing is simple, and when overhaul is required the design features
detailed below make this quick and straightforward, taking the engine out of
service for the least possible time ("exchange rather than repair"). In
particular, the cylinder-unit concept permits very easy exchange of cylinder
assemblies, while the electronic control and monitoring system provides for
condition-based maintenance.

    Design features
    The C25:33 is based on a compact and stiff nodular iron frame.  The charge
air receiver, lube oil channel and coolant transfer channel are incorporated
in the casting to eliminate pipework.  A continuous grain flow forged steel
crankshaft which has steel plate balance weights and runs in the latest
bearing material allows the cylinder centre distance to be kept the same as
the K series, in the interests of compactness and rigidity.  Full power can be
taken off either end of the crankshaft, and an additional main bearing allows
single-bearing alternators to be used.
    A key feature is the cylinder unit concept, in which a complete liner,
piston assembly, jacket and cylinder head can be drawn as a unit.  The
components are clamped together by the cylinder jacket and held down by four
cylinder head bolts.  A duct transfers air, exhaust and cooling water to and
from the head, and for speed of servicing the duct for each cylinder unit is
connected to its neighbours by quick-couplings.
    The cylinder liner and water jacket combination is of the "open-deck"
type, designed for very intensive cooling and high strength without stress
raisers in the critical top-end zone.
    The piston uses a steel crown carrying three rings, and a nodular cast
iron skirt.  In conjunction with the anti-polishing ring at the top of the
liner, the chrome-ceramic piston ring coating and the special honing structure
of the liners, this gives a long life with low and controlled oil consumption.
A three-part connecting rod has been developed, enabling the upper part to be
detached when drawing pistons without disturbing the big end bearing.
    Fuel pumps are mechanical, one per cylinder, and of the closed end design
for high pressure, with a simple two-step electronic timing feature.  Although
"common rail" injection has become an industry catch phrase, it was not
selected for the C-engine because it is not seen as having an advantage in the
generator-set applications typical of the new engine, and not yet durable
enough for un-restricted HFO operation.
    Impulse turbocharging is used, incorporating the latest design of all-
radial uncooled turbocharger, which can be mounted at either end of the engine
to suit the installation.  There is two-stage cooling of the charge air with
electronic temperature control.  Combined with a high-speed electronic
governor, the effect of these features is to give rapid response to load
changes and a good performance with minimum smoke under changing load
conditions.
    For freedom from pipework, ease of servicing and rational production, most
auxiliaries are mounted in a front-end module.  Plug-in components are easy to
exchange, with a minimum of joints, which is important for eliminating
leakages.  Integration has not, however, been carried to extremes.  For
example, the lube oil heat exchanger is mounted on the front-end module, but
incorporates a backing plate which could in principle be eliminated.  By
fitting it, a servicing advantage is won, as the cooler can be quickly
detached as a unit for overhaul and pressure testing, rather than being
dismantled on the engine.
    Other features for ease of overhaul include full use of hydraulic bolting
and large crankcase doors.  In general, the design of the C-engine caters for
the two main overhaul philosophies in the industry in that it can either be
stripped and serviced item by item, or complete modules can be exchanged to
minimise downtime, the old units being removed to the workshop for
refurbishment.  This also goes well with the ecology and sustainability
philosophies of our time.
    The C-engine is a particularly compact and powerful engine, which
incorporates the experience the company has built up in medium speed engines
since it began with 250mm bore units in the 1950s.  In recent years this
experience includes more than 1,500 K-series engines for all applications,
using gas and crude oil as fuels in addition to HFO.  Orders for the first
four production engines have already been received, with options for four
more.  The nine cylinder C25:33L engines are for generator set drive, with
four units in a power station arrangement supplying power for all requirements
on an offshore vessel.

    Notes:
    A downloadable picture of the engine is available at
http://www.rolls-royce.com/latestn/images/thumbnails19.htm