Home' Ships and Shipping : August 2009 Contents MAN Diesel has recently announced a further extension of its
line-up of large bore, four-stroke gas engines.
The new engine is the 51/60G, which like its 51/60DF
dual-fuel stablemate is derived from MAN Diesel's type 48/60
diesel engine platform.
The new engine uses a distillate fuel pilot injection system
to achieve reliable, stable ignition of lean air:gas mixtures in a
large-bore, open combustion chamber.
As a result, the new gas engine has one of the highest power
densities in the four-stroke gas engine field as well as low emissions
of oxides of nitrogen (NOx) and high fuel efficiency.
This choice of gas ignition technology also alleviates one of the
main weaknesses of spark-ignited gas engines, namely the
relatively short exchange intervals of even the best spark plugs.
By contrast, the liquid-fuel pilot ignition system of the 51/60G
gas engine exhibits the considerably longer service intervals typical
of diesel engine fuel-injection equipment.
Other advantages include low gas admission pressures, high and
stable ratings in hot and high power plant locations and excellent
load imposition, and load following characteristics.
"The 51/60G is now the largest, most powerful medium-speed
gas engine on the market," said Dr Stephan Mey, Head of MAN
Diesel's Augsburg-based Power Plant business unit.
"In particular, with the 51/60G, we are aiming to bring the
typical virtues of gas engines to power and cogeneration plants
with electrical outputs in the range 100 to 300MW class. These
benefits include intrinsically clean combustion of gases containing
methane combined with high fuel efficiencies and hence low
emissions of carbon dioxide.
In detail, the 51/60G is offered in a nine-cylinder inline version
and vee-configuration versions with twelve, 14 and 18 cylinders.
Standard rated outputs are 1,000kW per cylinder for 60Hz power
generation and 975kW per cylinder for 50Hz power generation. This
overall power range from 8,775kW to 18,000kW mechanical equates
to nominal generator set outputs of 8,538kW to 17,514kW electrical.
Advanced fuel/ignition control
The 51/60G makes extensive use of microprocessor control
technology to achieve its favourable economics and low emissions.
Gas admission is precisely controlled via electronically
controlled, electrically actuated valves in the 51/60G's inlet ports,
while pilot fuel injection is likewise via an electronically
controlled, electrically actuated common-rail system.
Common-rail injection technology allows flexible setting of
injection timing, duration and pressure for each cylinder. This
capability ensures the reliable ignition of lean air: fuel mixtures,
precise balancing of cylinder outputs and -- essential for a gas engine
-- rapid response to combustion knock signals on a cylinder-by-
cylinder basis. The pilot fuel quantity represents about 0.8 percent of
the energy required to achieve the 51/60G engine's standard
outputs, contributing to the engine's excellent NOx emissions.
Further enhancing both control of the air:fuel ratio and the
favourable efficiency of the 51/60G is the use of MAN Diesel's VTA
Variable Turbine Area turbocharger technology.
On the 51/60G, the VTA system replaces the traditional
method of air:fuel ratio control based on charge air bypassing.
Where a bypass system dissipates energy by expelling excess
charge air to the atmosphere, the VTA system uses variable
nozzle rang vanes ahead of the turbocharger turbine to precisely
match the charge-air output of the compressor to the engine's
demand for combustion air.
As with gas admission and pilot fuel injection, the VTA system
is electronically controlled.
On the fuel efficiency side, the overall effect of these
measures is specific consumption for natural gas plus the liquid
fuel pilot of 7,708kJ/kWhe (7,500 kJ/kWhm) for generator sets
powered by the 51/60G in NOx-optimised applications and
7,430kJ/kWhe (7,230kJ/kWhm) in efficiency optimised
applications. On the exhaust emissions side, NOx levels below
500mg/m3 at five percent dioxide mean the 51/60G readily
achieves both compliance with the limits prescribed in
Germany's TA luft clean air code and undercuts the limits
currently required by the World Bank by a wide margin.
"Naturally, we expect the 51/60G to be popular in cogeneration
and tri-generation application," Dr Mey noted. "In these plants,
thermal energy recovered from engine sources in used for heating,
cooling or generating process steam, resulting in energy utilisation
levels as high as 95 percent.
As with out large diesel engines, a further energy recovery
option on other from MAN Diesel with the 51/60G is a combined
cycle set up in which the exhaust heat of the 51/60G engine is
used to produce steam to drive a steam turbine generator.
In this way, the overall electrical output and efficiency of the
power plant can be increase by ten to 15 percent without
additional fuel costs."
For further information contact:
MAN Diesel, Germany. Web: www.manbw.com
The new MAN Diesel 51/60G
August 2009 SHIPS AND SHIPPING
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