Home  Locomotives, machines Locomotives Modernising the Fireless Steam Accumulator Locomotive
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Modernising the Fireless Steam Accumulator Locomotive |
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Written by Harry Valentine
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The accumulator locomotive was traditionally a fireless steam
locomotive used for shunting duties. All designs used a steam
accumulator that was essentially a thermos bottle laying on its side.To
be energised, the accumulator had to be at least 3/4 full of water.
Heating of this water was done by an external steam source. While some
designs used a coiled heat exchanger line, most later designs injected
superheated steam directly into the accumulator tank, using a
perforated pipe near the tank bottom. This design enabled rapid energy
re-charges (15 to 30-minutes) to be undertaken every few hours. A
cross-section layout of a fireless cooker is at
http://www.rr-fallenflags.org/porter/page44.jpg .
The last fireless locomotives were 0-4-0's built in Germany during the
early 1960's, by the Henschel group, based on research undertaken
during the 1930's by Prof. Gilli. These locomotives were small in size
and were designed to operate on accumulator pressures of 1,000-psig.
Some models used onboard, natural gas fired heaters and a coiled
monotube boiler. This arrangement used an external supply of natural
gas to heat the boiler and water pumped at high-pressure from an
external source. The fireless Henschel locomotives were smaller than
American built Heisler fireless steam locomotives, which operated on
lower accumulator pressures (200-psig). Nevertheless, a fully recharged
American Heisler 0-4-0 fireless locomotive of pre-WW2 vintage could
lumber along for distance of almost 95-miles on its own, or tow a train
of 10-loaded freight cars for distances of up to 20-miles. Porter
fireless locomotives operated on a tank pressure of 150-psig
(seehttp://www.rr-fallenflags.org/porter/porter-pd.html ). Using the
performance date obtained from early fireless locomotive designs,
extrapolations were undertaken to increase the operating range and
power output of a modern accumulator fireless locomotive, using larger
tanks storing higher pressures.
Modern manufacturing techniques can enable long, high-pressure
accumulator tanks to be built out of alloy steels, at very competitive
prices. A modern fireless design based on traditional concepts, could
use multiple high-pressure tanks, each with its own perforated
recharging pipe at tank bottom. Each tank could also be supplied with
its own onboard coiled monotube boiler. Monotube boilers have been
built that operate at over 1,000-psig, with 200-Hp thermal capability
and up to 85% heat transfer efficiency from combustion to steam
generation. Theoretically, such boilers would only be used for energy
recharging where no external supply of high-pressure superheated steam
is available. Performance improvements and extended operating range
would result from increased thermal storage capacity and improved
piston efficiency. Most thermal recharges would be done using
stationary, high-pressure water-tube boilers (up to 2,000-psig) fired
by gasified renewable (local) bio-fuels, or solar thermal energy stored
at high temperature. A multi-tank accumulator fireless locomotive could
be fully recharged within 15-30 minutes.
Research undertaken in Australia by Ted Pritchard (Pritchard
Steamhttp://prsteam.inventdata.com.au) into modernised uniflow (inlet
valve,exhaust ports) steam engines, has shown that in actual service,
the efficiency levels of a properly designed uniflow engine could be
double that of single-expansion piston engines. The modernised steam
piston engine is insulated using modern technology along its outer
(third) layer. It is also jacket-heated outside the cylinder walls to
yield higher performance levels. Modern valve control in the form of
precise inlet valve cut-off operation, further enhances efficiency.
Earlier fireless locomotives used only throttle valve control for
speed/powercontrol. Pritchard-type uniflow steam engines could be
mounted directly on the trucks (bogies) of modern fireless accumulator
locomotives. Analternative engine that can operate on the uniflow
principle is the Quasiturbine rotary engine, which can also be mounted
in the axletrucks/bogies (http://quasiturbine.promci.qc.ca/QTIndex.htm).
High-pressure accumulator tanks enable higher levels of energy to
bestored. A lower-pressure downstream tank can allow high-pressure
energy storage to be combined with lower-pressure pistons. This
approach is analogous the electronic "chopper" control used in DC
circuitry. Small bursts of power are sent to capacitors for temporary
storage, while inductors regulate reduce levels of power flow. A
similar system can be used in a steam storage system. In a steam
"chopper" system, a valve from the high pressure accumulators would
rapidly open (fully) and shut in response to pressure sensitive valves
in the cylinder-feed accumulator tanks (the steam "capacitor"). The
cylinder-feed accumulator could operate at pressures up to 300-psig,
while main storage tank pressures would hold pressure levels of up to
2,000-psig.
A modern steam accumulator locomotive could be built to the same
dimensions of the 3-level automobile carriers used on North American
railway systems. These cars are nearly 100-feet (30-m) between
couplers, 9-feet 6-inches (2.85-m) wide and with a height of
19-feet8-inches (6-m) above the head of the rail. To carry the
locomotive weight, a wheel/axle arrangement similar to that of the
American PennCentral GG1 locomotives' 4-6-6-4 layout may need to be
used, on a longer bogie/truck-centre spacing. The energy storage
capability could be up to 20-times that of a 1960's era Henschel
fireless, with at least 50% higher engine brake thermal efficiency than
traditional piston designs. Lumbering on its own at 40-Km/hr, the
modern accumulator fireless locomotive could have a range of up to
350-miles. A design built to the exterior dimensions of a passenger
rail coach (10'6" or3.2-m wide, 14'6" or 4.4-m high and 85' or 26-m
between couplers) could still store over 10-times the thermal energy of
a Henschel fireless loco. The main operating niche of such a locomotive
type would be in developing countries, where few paved roads exist and
where right-of way clearances would allow passage to large locomotives.
The condition of rail lines in some developing nations are such that
intercity trains rarely travel at speeds above 30-miles per hour
(50-Km/hr) and often slower. This type of operations allows for use of
low-powered locomotives that develop less than 1000-Hp (745-Kw). Stops
and lay-overs are frequent, operating characteristics that would favour
a large accumulator fireless steam locomotive. Recharging of
accumulator tanks could occur at rest stops or at terminals, every 25
to 50-miles. A large steam accumulator locomotive could pull a
passenger, freight or mixed train over a 50-mile journey segments,
distances that are not uncommon in developing countries. Certain rainy
regions in Asia, Central Africa (Congo area), Central and South America
would be potential candidates for modernised and improved traditional
accumulator locomotive operations. These are regions where rainfall is
frequent and water for locomotive operation would be available.
Such locomotives would require very low levels of maintenance and are
easily repairable. Fuel supplies for the stationary water-tube boilers
would be predominantly locally supplied. A small number of wayside
water-tube boilers could supply energy to a relatively large fleet of
accumulator locomotives, provided that they do not all need to be
re-charged at the same time in the same location (an extremely rare
occurrence). The cost of such a fleet of locomotives would be
comparatively low, while their availability levels would be quite high
(due to modern thermal insulation around the accumulator tanks) and the
speed over which fireless accumulator steam locomotives could be
re-charged (rarely more that 30-minutes using the perforated pipe with
a baffle above it). One person locomotive operation would prevail,
while added manpower (stationary engineers) would be needed to staff
the stationary water-tube boilers.
In sunny tropical countries where adequate water for steam locomotive
operation is available, solar thermal energy could be used to assist in
replenishing locomotive energy supply. Large solar heliostats would
collect intense solar thermal energy. Insulated fibre- optic lines made
from processes aluminium-oxide (purified & clear industrial
sapphire) would transmit the intense solar thermal energy into very
large, stationary, ceramic-lined and insulated thermal energy storage
tanks. Thermal energy would be stored in the high heats of fusion from
various metal-oxides. A low-cost material thermal storage material,
lithium-nitrate, occurs quite naturally across Southern Africa. The
addition of steam converts it to lithium-hydroxide, which has a latent
heat of fusion of 185-Btu/lb at 460-degrees C. Superior thermal storage
materials include a new generation of metallic oxide polymers
(super-molecules) such as aluminium-oxide polymers, having latent heats
of fusion up to 500-Btu/lb, near 500-degrees Celsius.
To prevent tank and water-tube corrosion, tank interiors and water-tube
exteriors would have to be lined with a corrosion resistant
materiallike carbon fibre or a high-temperature fluoro-plastic. Such
tanks can be used on board accumulator fireless locomotives to improve
performance and efficiency, by superheating steam prior to entry into
and expansion in the engine. A wide variety of thermal energy storage
materials have life expectancies of several million alternating
deep-drain and full-recharge cycles, with no loss of energy storage
capacity. The high cost of replacement electrical batteries may be
deferred indefinitely, by using such thermal storage technology. By
comparison, electric batteries become spent after several hundred
cycles of deep-cycle draining and recharging, requiring costly
replacement. A battery-electric system only returns some 50% of the
energy put in to it, dissipating the rest as heat mainly during the
charging cycle.
A modernised traditional fireless accumulator locomotive could be
economical to operate in terms of fuel supply and efficiency. It would
also be well suited to operating conditions that presently exist on
several "short-line" rail systems or railways in many developing
countries. Such locomotives would also be able to operate commuter
service (rapid energy recharge at the end of line) and tourist train
excursion service. They may even have application in commuter service
along non-electrified rail lines in some developed nations. In arid/dry
regions of the world, fireless locomotives would need to use a water
replenishing technology such as multiple expansion valves and
condensing radiators on the exhaust steam. Condensing effectiveness may
be improved by using an onboard sealed "cold-tank" containing either
ice or dry ice.
A variant of the fireless steam locomotive was the compressed air
locomotive, built by the same locomotive manufacturers (Porter,Baldwin,
Whistler, Henschel) as conventional and fireless steamtraction. The two
concepts can be combined into one, for short-distance operation only,
in extremely dry climates. The pressurised, saturated water would be
used as a thermal storage medium, instead of driving the wheels
directly and exhausting steam to the atmosphere. Externally energised
onboard water-pumps and monotube boilers would allow for energy
re-charging, much in the same manner as the extensively modified
locomotives that came from DLM. Compressed air (5,000-psi) stored in
tanks in a separate car, would be heated in tubes passing through the
water tanks, prior to expansion in a traction engine (such as a
quasiturbine). Heat may also be stored in a molten metallic
oxidepolymer in a lined (to combat corrosion) and insulated tank, with
coated (corrosion resistance) tubes passing through the thermal storage
tank.
The energy in such thermal storage tanks may also be used to energise a
closed-cycle Brayton turbine, using atmospheric air at varying pressure
levels as the working fluid. The Escher-Wyss division of Sulzer built
a2,000-Kw closed-cycle regenerative turbines operating on variable
pressure atmospheric air, delivering its optimal efficiency (15% in hot
weather to 32% in cool weather) between 20% to 80% of maximum power
output. In California,USA, the Power Now company has been testing a7-Kw
closed cycle turbine(http://www.companydr.com/vanaar/PowerNow/FAQs.htm)
using variable pressure air. This type of "steamless" variant of the
fireless locomotive would have to store its thermal energy supply in
the latent heat of fusion of a metallic-oxide polymer. It could operate
in short-line/branch-line operation on several types of railway
systems. In passenger service, it could pull tourist/excursion trains,
operate in low-frequency suburban commuter and pull short, light
intercity trains up to 300-km (at 100-km/hr). It could also pull light
intermodal trains (highway trailers on rail axles) of up to 50-cars, on
intercity journeys of up to 300-km.
Harry Valentine, Transportation Researcher, harrycv at hotmail.com
http://www.internationalsteam.co.uk/trains/newsteam/modern21.htm
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