ABSTRACT
Cryogens are effective thermal storage media which, when used for
automotive purposes, offer significant advantages over current and proposed
electrochemical battery technologies, both in performance and economy.
An automotive propulsion concept
is presented which utilizes liquid nitrogen as the working fluid for an open
Rankine cycle. The principle of operation is like that of a steam engine,
except there is no combustion involved. Liquid nitrogen is pressurized and then
vaporized in a heat exchanger by the ambient temperature of the surrounding
air. The resulting high – pressure nitrogen gas is fed to the engine converting
pressure into mechanical power.
The usage of cryogenic fuels has significant advantage over other fuel. Also,
factors such as production and storage of nitrogen and pollutants in the
exhaust give advantage for the cryogenic fuels.
INTRODUCTION
The importance of cars in the present world is increasing day by day. There are
various factors that influence the choice of the car. These include
performance, fuel, pollution etc. As the prices for fuels are increasing and
the availability is decreasing we have to go for alternative.
Here an automotive propulsion
concept is presented which utilizes liquid nitrogen as the working fluid for an
open Rankine cycle. When the only heat input to the engine is supplied by
ambient heat exchangers, an automobile can readily be propelled while
satisfying stringent tailpipe emission standards. Nitrogen propulsive systems
can provide automotive ranges of nearly 400 kilometers in the zero emission
mode, with lower operating costs than those of the electric vehicles currently
being considered for mass production. In geographical regions that allow ultra
low emission vehicles, the range and performance of the liquid nitrogen
automobile can be significantly extended by the addition of a small efficient
burner. Some of the advantages of a transportation infrastructure based on
liquid nitrogen are that recharging the energy storage system only requires
minutes and there are minimal environmental hazards associated with the
manufacture and utilization of the cryogenic"fuel". The basic
idea of nitrogen propulsion system is to utilize the atmosphere as the heat
source. This is in contrast to the typical heat engine where the atmosphere is
used as the heat sink.
Cryogenics
The use of extremely low temperatures
(cryogenic temperatures, which scientists define as below -244°F.) to boost the
performance and service life of critical components is now commonplace in the
racing industry and is becoming more and more prevalent in the manufacture of
high quality components. What was once considered by many to be a questionable
science is becoming a bedrock solid means of insuring the greater performance
of materials.
Why has it taken this long to gain
acceptance? It is extremely hard to get across to people that changes can be
made using cold. People easily grasp the fact that heat can be made to modify
solid materials. Heat treating is all around us. Humans have been
modifying metals with heat for over
7,000 years, and archeologists have found evidence that humans heated the rocks
to make better tools with them over 140,000 years ago. So, the use of heat is
second nature to most of us. We’ve only had extreme cold available to us in
commercial quantities for about 100 years.
Going colder was considered just a waste of
time. This attitude was (and is) so ingrained in people that when metallurgists
started to create diagrams on how the atoms in a metal worked with each other
at different temperatures, they went down to zero degrees Centigrade and
stopped. But research into Deep Cryogenic Treatment started to show it works
and that it works in materials where the old theories said it would not.
This finding has caused even the naysayers to take a second look..
Air Liquid, a noted manufacturer of the
liquid nitrogen used in cryogenic processing has bought processing equipment
and has assigned personnel to research the process in their French research
center (www.airliquide.com). They are also sponsoring research at Wayne State
University in Detroit.
• Increased electrical conductivity.
• Anecdotal evidence of changes in heat transfer.
In practice, cryogenic processing affects
the entire mass of the part. It is not a coating. This means that parts can be
machined after treatment without losing the benefits of the process.
Additionally, cryogenics apply to metals in general, not just ferrous metals.
For many years, it was assumed the only change caused by extreme cold was the
transformation of retained austenite to martensite in steel and iron. Because
of this, many misinformed engineers still believe that cryogenic processing is
“just a fix for bad heat treat.” It is now known that cryogenic processing has
a definite effect on copper, titanium, carbide, silver, brass, bronze,
aluminum, both austenitic and martensitic stainless steel, mild steel, and
others. It is also known that plastics such as nylon and phenolics show
property changes.
Racing Applications
Cryogenic processing can have a positive
effect on virtually every engine, transmission, and drive line part, as well as
many chassis parts. Increasing the durability of components in the vehicles is
the main reason for using cryogenic processing. The great thing about cryogenic
processing is that it allows an increase in durability without an increase in
weight or major modifications to component design. In addition, the use of
cryogenic processing has helped some racing teams reduce costs, enabling some
expensive parts to survive the stresses of racing for use in subsequent races.
Performance Advantages
Brakes and Clutches. Brakes of a racing car
take a real beating. It is not unusual for a racing vehicle to finish a race
with the brakes totally worn out. This is especially true during road races and
endurance racing, where brake rotors can get so hot they glow visibly at night.
Cryogenic processing can be applied to both rotors and pads. The net result is
two to three times the life of untreated components even under severe racing
conditions. As a side benefit, the rotors are less prone to crack or warp. It
is interesting that drivers report better braking action and feel. Some drivers
are so sold on the concept that they have their street vehicle equipped with
treated brakes. Clutches are a form of brake, and the results are very similar.
As an offshoot of racing development,
cryogenically treated rotors and pads are making their way into fleet
operations on the road. The U.S. Postal Service specifies cryogenic processing
for their rotors and is experiencing up to five times as many miles as they
were getting on the unprocessed rotors. Similarly, many police fleets are
starting to adopt treated rotors and pads. They, too, are experiencing large
maintenance savings on both parts and labor. What is metallurgically
interesting is that the brakes are a gray cast iron that has a pearlitic
structure. This rules-out the austenite to martensite transformation as the
mechanism for increased life.
Springs
Springs fail in one of two modes. They
either break or their spring constant starts to decline. Either way, it can
have catastrophic effects on the performance of the vehicle. Most valve springs
are made of specially made chrome silicon steel. The automotive valve spring is
a fatigue failure waiting to happen. It typically can lose up to one third of
its spring constant during a long race. In some forms of racing, it is just
hoped that the valve springs will last through the race. Some drag racers
routinely change the valve springs before every run down the drag strip to
ensure consistent performance.
The Chassis
The chassis itself is basically a very
large, complex spring, having numerous welds and using not very precise tubing.
The metals used here vary, depending on the type of racing. NASCAR frames are
made from 1020 steel; other forms of racing use 4140 steel. Of course, other
high strength, lightweight materials are also used. As the chassis experiences
vibration during the race, residual stresses in the welds and the tubing can
start to relieve. This causes the chassis to change shape during the race,
affecting the handling of the vehicle and therefore its speed.
Engines
Virtually every part of an engine will
respond to cryogenic processing, with all components exhibiting life increases.
Several component manufacturers are starting to take advantage of this and are
treating their racing components as part of their production. Some of the main
applications are:
Bearings: At least one racing
bearing manufacturer cryogenically treats babbited bearings as part of their
production process. They found it increased the life of the bearings and also
of the steel backing, which tended to fail in fatigue. It is interesting that
CRYOGENIC PROCESSING has an effect on the babbit metal of the bearings.
Similarly, bronze bushings used on wrist pins also wear considerably less when
treated. Many racers are processing ball bearings and roller bearings (typically
52100 steel) because they get a three to five fold increase in life. Rod ends
used in steering and suspension systems get the same treatment and performance
gains.
Cylinders, Pistons and Rings
Cryogenic processing of piston rings and
cylinder walls has been shown to reduce wear substantially. One go kart racing
customer claimed that he got a fivefold increase in engine life before he had
to freshen the engine. Better ring seal was born out in pressure readings on a
dynamometer. Apparently, this happens because the parts machine and hone better
after treatment as a consequence of a more uniform hardness distribution over
the surface of the part. CTP has done tests that show a significant reduction
in the standard deviation of hardness readings taken before and after cryogenic
processing. In some cases, the standard deviation is one third of what it was
before the process. Processed piston rings typically wear both less and more
evenly than untreated rings. More tribologically compatible with the cylinder walls,
they tend to flutter less due to the vibrational damping the process imparts
into the material and due to the more even hardness of both the rings and the
cylinder walls. All these factors combine to give better ring sealing, and
therefore more power.
Cryogenic processing of engine blocks also
stabilizes the blocks and reduces warping and distortion due to vibration and
heat during use. . Even head gaskets
benefit because the armor around the combustion chamber is subject to both
thermal cyclic fatigue and to flexing fatigue.
Keys to the Process
Success of cryogenic processing is
critically dependent on the equipment in which the processing is done. There
are companies that will dip your components in liquid nitrogen and pronounce
them “treated.”. This is a video where two Lincoln
Laboratory scientists put a rubber stopper into liquid nitrogen. The result is
that it explodes. Metal parts are stressed in much the same way by immersion.
The best cycles are those that reduce the
temperature of the part slowly, typically going down to -300°F in eight hours
or more. The part should then be held at -300°F for an extended time that
depends on the material being processed. Research is indicating that the time
at-300°F is very dependent on the alloy being processes. The hold part of the
cycle can be as short as 8 hours or as long as 60. The hold part of the cycle
is followed by a slow rise in temperature to ambient. Many alloys need at
least one heat tempering cycle to finish the process.
THEORY BEHIND THE CRYOCAR
Researchers at the University of
Washington are developing a new zero-emission automobile propulsion concept
that uses liquid nitrogen as the fuel. The principle of operation is like that
of a steam engine, except there is no combustion involved. Instead, liquid
nitrogen at –320° F (–196° C) is pressurized and then vaporized in a heat
exchanger by the ambient temperature of the surrounding air.
This heat exchanger is like the radiator of a car but
instead of using air to cool water, it uses air to heat and boil liquid nitrogen.
The resulting high-pressure nitrogen gas is fed to an engine that operates like
a reciprocating steam engine, converting pressure
to mechanical power. The only exhaust is nitrogen, which is the major
part.
The LN2000 is an operating
proof-of-concept test vehicle, a converted 1984 Grumman-Olson Kubvan mail
delivery van. Applying LN2 as a portable thermal storage medium to
propel both commuter and fleet vehicles appears to be an attractive means to
meeting the ZEV regulations soon to be implemented. Pressurizing the working
fluid while it is at cryogenic temperatures, heating it up with
ambient air, and expanding it in reciprocating engines is a straightforward
approach for powering pollution free vehicles. Ambient heat exchangers that
will not suffer extreme icing will have to be developed to enable wide utility
of this propulsion system. Since the expansion engine operates at sub-ambient
temperatures, the potential for attaining quasi-isothermal operation appears
promising. The engine, a radial five-cylinder 15-hp air motor, drives the front
wheels through a five-speed manual Volkswagen transmission. The liquid nitrogen
is stored in a thermos-like stainless steel tank. At present the tank is
pressurized with gaseous nitrogen to develop system pressure but a cryogenic liquid
pump will be used for this purpose in the future. A preheater, called an
economizer, uses leftover heat in the engine's exhaust to preheat the liquid
nitrogen before it enters the heat exchanger. The specific energy densities
of LN2 are 54 and 87 W-h/kg-LN2 for the adiabatic and isothermal expansion
processes, respectively, and the corresponding amounts of cryogen to provide a
300 km driving range would be 450 kg and 280 kg. Many details of the
application of LN2 thermal storage to ground transportation remain to be
investigated; however, to date no fundamental technological hurdles have yet
been discovered that might stand in the way of fully realizing the potential
offered by this revolutionary propulsion concept.
Liquid nitrogen is generated
by cryogenic or Sterling engine coolers that liquefy the main component of air,
nitrogen (N2). The cooler can be powered by electricity or through direct
mechanical work from hydro or wind turbines.
DESCRIPTION:
Liquid nitrogen is
distributed and stored in insulated containers. The insulation reduces heat
flow into the stored nitrogen; this is necessary because heat from the
surrounding environment boils the liquid, which then transitions to a gaseous
state. Reducing inflowing heat reduces the loss of liquid nitrogen in storage.
The requirements of storage prevent the use of pipelines as a means of
transport. Since long-distance pipelines would be costly due to the insulation
requirements, it would be costly to use distant energy sources for production
of liquid nitrogen. Petroleum reserves are typically a vast distance from
consumption but can be transferred at ambient temperatures.
• The basic idea of the LN2 propulsion
system is to utilize the atmosphere as a heat source & a cryogen as a heat
sink in thermal power cycle
• This is a contrast to typical thermal
engines which utilize an energy source at temperature significantly above
ambient & use atmosphere as a heat sink
• The both case the efficiency of
conversion of thermal energy of the source to work (W) is limited by a Carnot
efficiency
The efficiency η is defined to be
• W is the work done by the system
(energy exiting the system as work),
• QH is the heat put into the system
(heat energy entering the system),
• TC is the absolute temperature of the
cold reservoir, and
• TH is the absolute temperature of the
hot reservoir.• SB is the maximum system entrop• SA is the minimum system
entrophy
WORKING OF CRYOCAR
Liquid nitrogen vehicle
A liquid nitrogen vehicle is powered
by liquid n itrogen, which is stored in a tank. The
engine works by heating the liquid nitrogen in a heat
exchanger, extracting heat from the ambient air and using the resulting
pressurized gas to operate a piston or rotary engine. Vehicles propelled by
liquid nitrogen have been demonstrated, but are not used commercially.
Liquid nitrogen propulsion may also be
incorporated in hybrid systems, e.g., battery electric propulsion and fuel
tanks to recharge the batteries. This kind of system is called a hybrid liquid
nitrogen-electric propulsion. Additionally, regenerative braking can also be used in
conjunction with this system.
Liquid nitrogen is generated by cryogenic
or Stirling engine coolers that liquefy the main
component of air, nitrogen (N2). The cooler can be powered by
electricity or through direct mechanical work from hydro
or wind
turbines.
Liquid nitrogen is distributed and stored in
insulated
containers. The insulation reduces heat flow into the stored nitrogen; this
is necessary because heat from the surrounding environment boils the liquid,
which then transitions to a gaseous state. Reducing inflowing heat reduces the
loss of liquid nitrogen in storage. The requirements of storage prevent the use
of pipelines as a means of transport. Since long-distance pipelines would be costly
due to the insulation requirements, it would be costly to use distant energy
sources for production of liquid nitrogen. Petroleum reserves are typically a
vast distance from consumption but can be transferred at ambient temperatures.
Liquid nitrogen consumption is in essence
production in reverse. The Stirling
engine or cryogenic heat engine offers a way to power vehicles and a means
to generate electricity. Liquid nitrogen can also serve as a direct coolant for
refrigerators,
electrical
equipment and air conditioning units. The consumption of liquid
nitrogen is in effect boiling and returning the nitrogen to the
atmosphere.
Cost of production
Liquid nitrogen production is an
energy-intensive process. Currently practical refrigeration plants producing a
few tons/day of liquid nitrogen operate at about 50% of Carnot efficiency.
Energy density of liquid nitrogen
Any process that relies on a phase-change of a substance will have much lower energy densities than processes involving a chemical reaction in a substance, which in turn have lower energy densities than nuclear reactions. Liquid nitrogen as an energy store has a low energy density. Liquid hydrocarbon fuels by comparison have a high energy density. A high energy density makes the logistics of transport and storage more convenient. Convenience is an important factor in consumer acceptance. The convenient storage of petroleum fuels combined with its low cost has led to an unrivaled success. In addition, a petroleum fuel is a primary energy source, not just an energy storage and transport medium.
For an isothermal expansion engine to have a
range comparable to an internal combustion engine, a 350-litre (92 US gal)
insulated onboard storage vessel is required. A practical volume, but a noticeable increase over the typical 50-litre
(13 US gal) gasoline tank. The addition of more complex power cycles would
reduce this requirement and help enable frost free operation. However, no
commercially practical instances of liquid nitrogen use for vehicle propulsion
exist.
Frost formation
Unlike internal combustion engines, using a
cryogenic working fluid requires heat exchangers to warm and cool the working
fluid. In a humid environment, frost formation will prevent heat flow and thus
represents an engineering challenge. To prevent frost build up, multiple
working fluids can be used. This adds topping cycles to ensure the heat
exchanger does not fall below freezing. Additional heat exchangers, weight,
complexity, efficiency loss, and expense, would be required to enable frost
free operation.
However efficient the insulation on the
nitrogen fuel tank, there will inevitably be losses by evaporation to the
atmosphere. If a vehicle is stored in a poorly ventilated space, there is some
risk that leaking nitrogen could reduce the oxygen concentration in the air and
cause asphyxiation.
Since nitrogen is a colorless and odourless gas that already makes up 78% of
air, such a change would be difficult to detect.
Cryogenic liquids are hazardous if spilled.
Liquid nitrogen can cause frostbite and can make some materials extremely brittle.
As liquid N2 is colder than 90.2K, oxygen
from the atmosphere can condense. Liquid oxygen can spontaneously and violently
react with organic chemicals, including petroleum products like asphalt.
Tanks
The tanks must be designed to safety
standards appropriate for a pressure
vessel, such as ISO 11439
The storage tank may be made of:
·
steel
·
aluminium
·
carbon
fiber
·
Kevlar
·
other materials, or
combinations of the above.
The fiber materials are considerably lighter
than metals but generally more expensive. Metal tanks can withstand a large
number of pressure cycles, but must be checked for corrosion periodically.
Liquid nitrogen, LN2, is commonly transported in insulated tanks, up to 50
litres, at atmospheric pressure. These tanks, being non-pressure tanks they are
not subject to inspection. Very large tanks for LN2 are sometimes pressurized
to less than 25 psi to aid in transferring the liquid at point of use.
Emissionoutput Like other non-combustion energy storage technologies, a liquid nitrogen vehicle displaces the emission source from the vehicle's tail pipe to the central electrical generating plant. Where emissions-free sources are available, net production of pollutants can be reduced. Emission control measures at a central generating plant may be more effective and less costly than treating the emissions of widely dispersed vehicles.
• A car powered by liquid nitrogen may be seen cruising the streets of Bishops Stortford.
• Cylinder injection of a heat transfer
fluid followed by liquefied gas raises efficiency to a point where fuel costs
are comparable with petrol, but with no pollution.
• As well as solving a problem which
has long bugged all Rankine cycle engines, it leads to vehicles which are
totally pollution free, without the cost and weight penalties incurred by
batteries, and are also intrinsically safe, a matter of great interest to the
oil and gas industries.
• The idea of providing forward motion
from the boiling of a liquid and the subsequent expansion of a gas has been
around since the end of the eighteenth century. While much used in the age of
steam, the problems of heat transfer result in very poor thermal efficiencies
unless the machines are of power station size.
.• • This engine is two strokes.
• The induction stroke starts by
drawing in the heat exchange fluid, which in his case is a conventional mix of
ethylene glycol based car anti-freeze and water.
• Liquid nitrogen is then injected
subsequently from a separate nozzle. (If it was injected simultaneously, the
liquid nitrogen would freeze the heat transfer fluid as it entered, blocking
the injection port).
• The heat transfer fluid possesses
sufficient heat capacity to both boil the liquid nitrogen and heat it all the
way up to ambient temperature.
• The pressure pushes the piston down
the cylinder, and as it does so, it absorbs more heat from the heat transfer
fluid to maintain its temperature at ambient.
• At bottom dead centre, the exhaust
valve opens, and the expanded nitrogen and heat transfer fluid are allowed to
escape.
• Before reaching the atmosphere, the
mixture passes through a separator to recover the heat transfer fluid. The
latter passes through a radiator to warm it up fully to ambient on its way back
to the cylinder.
• At a cost from Air Products of
10p/litre, this allows the car to achieve a similar fuel cost per mile to that
achieved using petrol. A new two cylinder engine with twice the powerouptut is
now undergoing tests.
POWER CYCLE
The Rankine cycle most closely describes the
process by which steam-operated heat
engines most commonly found in power
generation plants generate power. The two most common heating processes
used in these power plants are nuclear
fission and the combustion of fossil -fuels such as coal, natural gas,
and oil.
The Rankine cycle is sometimes referred to
as a practical Carnot cycle because, when an efficient turbine is
used, the TS
diagram begins to resemble the Carnot cycle. The main difference is that
heat addition (in the boiler) and rejection (in the condenser) are isobaric
in the Rankine cycle and isothermal in the theoretical Carnot cycle. A
pump is used to pressurize the working fluid received from the condenser as a
liquid instead of as a gas. All of the energy in pumping the working fluid
through the complete cycle is lost, as is most of the energy of vaporization of
the working fluid in the boiler. This energy is lost to the cycle because the
condensation that can take place in the turbine is limited to about 10% in
order to minimize blade erosion; the vaporization energy is rejected from the
cycle through the condenser. But pumping the working fluid through the cycle as
a liquid requires a very small.
The efficiency of a Rankine cycle is usually
limited by the working fluid. Without the pressure reaching super critical levels for the
working fluid, the temperature range the cycle can operate over is quite small.
The working fluid in a Rankine cycle follows
a closed loop and is reused constantly. The water vapor with entrained
droplets often seen billowing from power stations is generated by the cooling
systems (not from the closed-loop Rankine power cycle) and represents the waste
energy heat (pumping and vaporization) that could not be converted to useful
work in the turbine. Note that cooling
towers operate using the latent heat of vaporization of the cooling fluid.
While many substances could be used in the Rankine cycle, water is usually the
fluid of choice due to its favorable properties, such as nontoxic and
nonreactive chemistry, abundance, and low cost, as well as its thermodynamic properties.
The four processes in the Rankine cycle
Ts diagram of a typical Rankine cycle operating between pressures of 0.06bar and 50bar
There are four processes in the Rankine
cycle. These states are identified by numbers (in brown) in the diagram to the
left.
·
Process 1-2:
The working fluid is pumped from low to high pressure. As the fluid is a liquid
at this stage the pump requires little input energy.
·
Process 2-3:
The high pressure liquid enters a boiler where it is heated at constant
pressure by an external heat source to become a dry saturated vapor. The input
energy required can be easily calculated using mollier
diagram or h-s
chart or enthalpy-entropy chart
also known as steam
tables.
·
Process 3-4:
The dry saturated vapor expands through a turbine,
generating power. This decreases the temperature and pressure of the vapor, and
some condensation may occur. The output in this process can be easily
calculated using the Enthalpy-entropy chart
or the steam tables.
·
Process 4-1:
The wet vapor then enters a condenser
where it is condensed at a constant temperature to become a saturated liquid.
Variables
Heat flow rate to or from the system
(energy per unit time)
|
|
Mass
flow rate (mass per unit time)
|
|
Mechanical power
consumed by or provided to the system (energy per unit time)
|
|
ηtherm
|
Thermodynamic efficiency of the
process (net power output per heat input, dimensionless)
|
FACTORS EFFECTING ON
CRYOCARS
COST OF PRODUCTION
Liquid
nitrogen production is an energy-intensive process. Currently practical
refrigeration plants producing a few tons/day of liquid nitrogen operate at
about 50% of Carnot efficiency.
ENERGY DENSITY OF LIQUID NITROGEN
Any
process that relies on a phase-change of a substance will have much lower
energy densities than processes involving a chemical reaction in a substance,
which in turn have lower energy densities than nuclear reactions. Liquid
nitrogen as an energy store has a low energy density. Liquid hydrocarbon fuels
by comparison have a high energy density. A high energy density makes the
logistics of transport and storage more convenient. Convenience is an important
factor in consumer acceptance. The convenient storage of petroleum fuels
combined with its low cost has led to an unrivaled success. In addition, a
petroleum fuel is a primary energy source, not just an energy storage and
transport medium.
The
energy density — derived from nitrogen's isobaric heat of vaporization and
specific heat in gaseous state — that can be realized from liquid nitrogen at
atmospheric pressure and zero degrees Celsius ambient temperature is about 97 watt-hours
per kilogram (W-hr/kg). This compares with about 3,000 W-hr/kg for a gasoline
combustion engine running at 28% thermal efficiency, 30 times the density of
liquid nitrogen used at the Carnot efficiency.
FROST FORMATION:- Unlike internal combustion engines, using a
cryogenic working fluid requires heat exchangers to warm and cool the working
fluid. In a humid environment, frost formation will prevent heat flow and thus
represents an engineering challenge. To prevent frost build up, multiple working
fluids can be used. This adds topping cycles to ensure the heat exchanger does
not fall below freezing. Additional heat exchangers, weight, complexity,
efficiency loss, and expense
McCosh,”Emerging Technologies for the
supercar,” popular science ,june 1994
SAFETY
However
efficient the insulation on the nitrogen fuel tank, there will inevitably be
losses by evaporation to the atmosphere. If a vehicle is stored in a poorly
ventilated space, there is some risk that leaking nitrogen could reduce the
oxygen concentration in the air and cause asphyxiation. Since nitrogen is a
colorless and odourless gas that already makes up 78 % of air, such a change
would be difficult to detect.26
Cryogenic liquids are hazardous if
spilled. Liquid nitrogen can cause frostbite and can make some materials
extremely brittle.
As liquid N2 is colder than 90.2K,
oxygen from the atmosphere can condense. Liquid oxygen can spontaneously and
violently react with organic chemicals, including petroleum products like
asphalt
Since the liquid to gas expansion
ratio of this substance is 1:694, a tremendous amount of force can be generated
if liquid nitrogen is rapidly vaporized. In an incident in 2006 at Texas
A&M University, the pressure-relief devices of a tank of liquid nitrogen
were sealed with brass plugs. As a result, the tank failed catastrophically,
and exploded.
The tanks must be designed to safety
standards appropriate for a pressure vessel, such as ISO 11439.
The
storage tank may be made of:
Steel,
Aluminium,
Carbon
fiber,
Kevlar,
Other
materials or combinations of the above.
The fiber materials are considerably
lighter than metals but generally more expensive. Metal tanks can withstand a
large number of pressure cycles, but must be checked for corrosion
periodically.
EMISSION
OUTPUT
Like other non-combustion energy
storage technologies, a liquid nitrogen vehicle displaces the emission source
from the vehicle's tail pipe to the central electrical generating plant. Where
emissions-free sources are available, net production of pollutants can be
reduced.Emission control measures at a central generating plant may be more
effective and less costly than treating the emissions of widely dispersed
vehicles .
ADVANTAGES AND DISADVANTAGES Liquid nitrogen vehicles are comparable in many ways to electric vehicles, but use liquid nitrogen to store the energy instead of batteries. Their potential advantages over other vehicles include:
·
Much like electrical
vehicles, liquid nitrogen vehicles would ultimately be powered through the
electrical grid, which makes it easier to focus on reducing pollution from one
source, as opposed to the millions of vehicles on the road.
·
Transportation of the
fuel would not be required due to drawing power off the electrical grid. This
presents significant cost benefits. Pollution created during fuel
transportation would be eliminated.
·
Lower maintenance costs
·
Liquid nitrogen tanks
can be disposed of or recycled with less pollution than batteries.
·
Liquid nitrogen
vehicles are unconstrained by the degradation problems associated with current
battery systems.
·
The tank may be able to
be refilled more often and in less time than batteries can be recharged, with
re-fueling rates comparable to liquid fuels.
Disadvantages The principal disadvantage is the inefficient use of primary energy. Energy is used to liquefy nitrogen, which in turn provides the energy to run the motor. Any conversion of energy has losses. For liquid nitrogen cars, electrical energy is lost during the liquefaction process of nitrogen.
Liquid nitrogen is not available in public refueling stations nor is
there a distribution system in place.
very friendly, even
if fossil fuels are used to generate the electric power required. The exhaust
gases produced by burning fossil fuels in a power plant contain not only carbon
dioxide and gaseous pollutants, but also all the nitrogen from the air used in
the combustion. By feeding these exhaust gases to the nitrogen liquefaction
plant, the carbon dioxide and other undesirable products of combustion can be
condensed and separated in the process of chilling the nitrogen, and thus no
pollutants need be released to the atmosphere by the power plant. The
sequestered carbon dioxide and pollutants could be injected into depleted gas
and oil wells, deep mine shafts, deep ocean subduction zones, and other
repositories from which they will not diffuse back into the atmosphere, or they
could be chemically processed into useful or inert substances. Consequently,
the implementation of a large fleet of liquid nitrogen vehicles could have much
greater environmental benefits than just reducing urban air pollution as
desired by current zero-emission vehicle mandates..
The above figure shows how a
liquid nitrogen based propulsion cycle fares against the various
electrochemical storage media mentioned earlier. Specific energy is a useful
figure of merit because it correlates closely with range. Even the next
generation, nickel-metal hydride battery, only matches the performance of the
isothermal open Rankine cycle.
CONCLUSION
The potential for utilizing the
available energy of liquid nitrogen for automotive propulsion looks very
promising. Time to recharge (refuel), infrastructure investment, and environmental
impact are among the issues to consider, in addition to range and performance,
when comparing the relative merits of different ZEV technologies. The
convenience of pumping a fluid into the storage tank is very attractive when
compared with the typical recharge times associated with lead-acid batteries.
Manufacturing LN2 from ambient air inherently removes small quantities of
atmospheric pollutants and the installation of large-scale liquefaction
-equipment at existing fossil-fuel power stations could make flue gas
condensation processes economical and even eliminate the emissions of CO2.
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