Feature 2
emissions, in combination with improved
dynamic behaviour of the engine-
turbocharger system.
The VTA system consists of a nozzle
ring equipped with adjustable vanes which
replaces the fixed vane nozzle rings fitted in
MAN Diesel’s standard TCA turbochargers.
In this way, VTA technology can be readily
retrofitted to turbochargers already in the
field. By adjusting the pitch of the vanes,
the pressure of the exhaust gases can be
regulated and the output of the compressor
optimised at all points on the engine’s
performance map.
In order to minimise thermal hysteresis
and improve adjustment accuracy, each
vane has a lever, which is directly connected
to a control ring. The control ring is
actuated by an electric positional motor
with integrated reduction gear whose the Man Diesel Vta system is under test on a six-cylinder, 46cm bore 6s46Mc-c engine
development was an integral part of MAN built by Man Diesel’s croatian licensee Brodosplit powering the shallow draught tanker
Diesel’s VTA solution. The adjustable vanes Stena President. here, the engine is seen during shop testing.
are manufactured in heat- and erosion-
resistant steel alloy, and careful selection of
fits and materials ensures operation under actuation and is one of two engines installed auxiliary-blowers, depending on the engine
all conditions without sticking, especially in a twin engine propulsion system aboard load-profile.
in applications on engines burning heavy the 70,000tonnes, shallow draught tanker On a slightly longer timeframe, MAN
fuel oil (HFO). Stena President, built at the Brodosplit Diesel is also pursuing single and two-stage
Control of vane position is fully shipyard for the Stena Concordia Maritime high-pressure turbocharging. In its single
electronic with feedback or open-loop shipping line. stage, high-pressure turbocharging concept,
control with mapped vane adjustment. Inclusion of VTA technology on the MAN Diesel employs optimised Series
A comprehensive range of control axial TCA55 turbocharger allows up to compressor wheels to achieve pressure
signals can be used, including charge air 0.5bar variation in compressor output ratios up to 6bar at 80% turbocharger
pressure after the compressor and exhaust pressure at part load. Overall results efficiency.
gas temperature before and after the show the expected improvements at By employing the inter-stage cooler
turbocharger. In this way, MAN Diesel part load in terms of fuel consumption, between the two turbocharging stages,
states, it can offer control packages precisely considerable reductions in emissions the energy required to compress the
tailored to a specific application, including of soot and unburnt hydrocarbons, as intake air to high pressure is considerably
both mechanically-controlled engines and well as improved engine response under reduced compared to a system without
engines with electronic management. For load changes. It was also demonstrated this feature.
retrofit applications, MAN Diesel will offer that VTA technology gave a useful These high-end turbocharging
complete packages including the VTA new dimension to the mechanically- techniques offer decisive improvements
nozzle ring, the actuator, and the associated controlled engine. The effects are said to to engine performance data, especially
control system. be comparable to the use of variable valve by enabling strong Miller valve timing to
The first application for an axial timing and electronic engine control. improve the trade-off between SFOC and
turbocharger with VTA technology is a To attain the best possible comparison low NOx emissions. As the comparative
two-stroke, low-speed marine engine, the engine with VTA turbocharger runs table shows, mean cylinder pressures over
while a radial turbocharger with VTA alongside a second 6S46MC-C engine 30bar are possible while the strong Miller
technology is being tested on MAN Diesel’s with conventional turbocharging. process allows NOx reductions in excess
revolutionary 32/40 PGI gas engine. Specifically, the benefits of the higher of 30% savings with no SFOC penalty.
The VTA system on an axial turbocharger scavenging pressures in part-load operation At the same time an increase of up to
is also under test on a six cylinder, 46cm bore provided by the VTA turbocharger include 8% is possible in thermal engine efficiency
6S46MC-C engine built by MAN Diesel’s lower SFOC at part-load, improved torque combined with a 2% improvement in
Croatian licensee Brodosplit. The HFO- and engine acceleration, lower combustion fuel efficiency, while future potential for
burning 6S46MC-C features mechanically- chamber temperatures, and the exacted SFOC and NOx savings is also considered
controlled fuel injection and exhaust valve savings in electrical energy to drive the substantial. NA
The Naval Architect March 2008 57
NA Mar 08 - p56+
57.indd 57 10/03/2008 12:04:20
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