CRYOCAR

CRYOCAR

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. 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."

DEPT. AUTOMOBILE ENGG-TOCE

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CONTENTS 1. INTRODUCTION……………………………………………………………. 2. LIQUID NITROGEN VEHICLE…………………………………………… 3. LIQUID NITROGEN MANUFACTURE…………………………………… 4. LIQUID NITROGEN PROPULSION CYCLE………………...................... 4.1 PATRS OF A LIQUID NITROGEN PROPULSION CYCLE 4.1.1 Cryogen Storage Vessel 4.1.2 Pump 4.1.3 Economizer 4.1.4 Expander 4.1.5 Heat Exchanger 5. PRINCIPLE OF OPERATION…………………………………………………. 6. POWER CYCLE………………………………………………………………..... 7. EFFICIENCY…………………………………………………………………….. 8. ADVANTAGES………………………………………………………………….. 8.1 Compare to Electric Cars 8.2 As compared to Fossil Fuels 9. TECHNICAL ISSUES………………………………………………………….… 10. CONCLUSION………………………………………………………………….. 11. REFERENCES…………………………………………………………………..


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LIST OF FIGURES Figure No.

Title

Page No.

Fig.1

LN2000 Vehicle

Fig.2

P-T Chart showing Nitrogen Liquification

Fig.3

Block Diagram of LN manufacture

Fig.4

LN propulsion cycle

Fig.5

Parts of LNPC

Fig 6

Expander Engine

Fig 7

Heat Exchanger

Fig 8

Graph of Temp vs Entropy


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CHAPTER 1 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 choice. A significant fraction of the lead produced each year is used in leadacid batteries for automobiles and a typical EV requires 20-30 conventional batteries to have a useful range. The growing public awareness of the health hazards arising from elevated concentrations of lead in the environment has resulted in a steady decrease in the amounts of lead used in industry and personal products over the years. In addition, it has been found that the pollution control practices at the mine heads and ore smelters have not prevented serious degradation of their surroundings. Thus, it is highly probable that the environmental impact of the increased mining and refining of lead ore, to meet the needs of a transportation infrastructure based on lead-acid batteries, could completely negate the benefits expected from the elimination of tailpipe emissions. It appears that liquid nitrogen (LN2) can be used in a zero-emission propulsion system that is as effective and probably more economical to operate than the high performance battery systems currently under development. 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 kilometres 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".


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CHAPTER 2 LIQUID NITROGEN VEHICLE Researchers at the University of Washington are develop 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 constituent of our atmosphere.

Fig.1 LN2000 Vehicle The LN2000 is an operating proof-of-concept test vehicle, a converted 1984 GrummanOlson 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 DEPT. AUTOMOBILE ENGG-TOCE

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CRYOCAR 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 fivespeed 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 concept.


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CHAPTER 3 LIQUID NITROGEN MANUFACTURE

Inter cooler

Dust Precipitator

Fig.2 P-T Chart showing Nitrogen Liquification

LN2

Nozzle

Fig.3 Block Diagram of LN manufacture


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CRYOCAR  Liquid Nitrogen is the widely produced and most common cryogen.  It is mass produced in air liquefaction plants  The liquefaction process is very simple.  The cost of the LN2 "fuel" is expected to be reasonable. The primary expense for producing LN2 is the energy cost for compression of air. Cryogenic separation of nitrogen from other condensable in air typically requires only a very small fraction of the total energy.  Normal, atmospheric air is passed through dust precipitator and pre-cooled.  It is then compressed inside large turbo pumps to about 100 atmospheres (10.13 MPa).  Once the air has been cooled to room temperature it is allowed to expand rapidly through a nozzle into an insulated chamber.  By running several cycles the temperature of the chamber becomes low enough. The air entering it starts to liquefy.  Liquid nitrogen is removed from the chamber by fractional distillation and is stored inside well-insulated Dewar flasks or Storage vessel.

CHAPTER 4 LIQUID NITROGEN PROPULSION CYCLE DEPT. AUTOMOBILE ENGG-TOCE

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Fig.4 LN propulsion cycle

4.1 PARTS OF A LIQUID NITROGEN PROPULSION CYCLE

Fig.5 parts of LNPC The main parts of a liquid nitrogen propulsion system are: 1. Cryogen Storage Vessel.


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CRYOCAR 2. Pump. 3. Economizer. 4. Expander Engine. 5. Heat exchanger. The parts and their functions are discussed in detail below:

4.1.1 Cryogen Storage Vessel: The primary design constraints for automobile cryogen storage vessels are: resistance to deceleration forces in the horizontal plane in the event of a traffic accident, low boil-off rate, minimum size and mass and reasonable cost. Crash-worthy cryogen vessels are being developed for hydrogen-fueled vehicles that will prevent loss of insulating vacuum at closing speeds of over 100 km/h.18 Moderately high vacuum (10-4 torr) with super insulation can provide boil-off rates as low as 1% per day in 200 liter (53 gal) containers. Using appropriate titanium or aluminum alloys for the inner and outer vessels, a structurally reinforced Dewar could readily have a seven-day holding period.

4.1.2 Pump: The pump is used to pump the liquid nitrogen into the engine. The pump which are used for this purpose have an operating pressure ranging between 500 – 600 Psi. As the pump, pumps liquid instead of gas, it is noticed that the efficiency is high.

4.1.3 Economizer: A preheater, called an economizer, uses leftover heat in the engine's exhaust to preheat the liquid nitrogen before it enters the heat exchanger. Hence the economizer acts as a heat exchanger between the incoming liquid nitrogen and the exhaust gas which is left out. This is similar to the preheating process which is done in compressors. Hence with the use of the economizer, the efficiency can be improved. The design of this heat exchanger is such as to prevent frost formation on its outer surfaces.

4.1.4 Expander:


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Fig 6 Expander Engine The maximum work output of the LN2 engine results from an isothermal expansion stroke. Achieving isothermal expansion will be a challenge, because the amount of heat addition required during the expansion process is nearly that required to superheat the pressurized LN2 prior to injection. Thus, engines having expansion chambers with high surface-to-volume ratios are favored for this application. Rotary expanders such as the Wankel may also be well suited. A secondary fluid could be circulated through the engine block to help keep the cylinder walls as warm as possible. Multiple expansions and reheats can also be used although they require more complicated machinery. Vehicle power and torque demands would be satisfied by both throttling the mass flow of LN2 and by controlling the cut-off point of N2 injection, which is similar to how classical reciprocating steam engines are regulated. The maximum power output of the propulsion engine is limited by the maximum rate at which heat can be absorbed from the atmosphere. The required control system to accommodate the desired vehicle performance can be effectively implemented with either manual controls or an on-board computer.

4.1.5 Heat Exchanger: DEPT. AUTOMOBILE ENGG-TOCE

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Fig 7 Heat Exchanger The primary heat exchanger is a critical component of a LN2 automobile. Since ambient vaporizers are widely utilized in the cryogenics and LNG industries, there exists a substantial technology base. To ensure cryomobile operation over a wide range of weather conditions, the vaporizer should be capable of heating the LN2 at its maximum flow rate to near the ambient temperature on a cold winter day. Since reasonable performance for personal transportation vehicles can be obtained with a 30 kW motor, the heat exchanger will be sized accordingly. The heat absorbed from the atmosphere can, in principle, be converted to useful mechanical power with about 40% efficiency. Thus the heat exchanger system should be prudently designed to absorb at least 75 kW from the atmosphere when its temperature is only 0°C. To estimate the mass and volume of the primary heat exchanger, it was modeled as an array of individually fed tube elements that pass the LN2 at its peak flow rate without excessive pressure drop. Each element is a 10 m long section of aluminum tubing having an outside diameter of 10 mm and a wall thickness of 1 mm. They are wrapped back and forth to fit within a packaging volume having 0.5 m x 0.4 m x 0.04 m dimensions and are arrayed in the heat exchanger duct. Incoming air will pass through a debris deflector and particulate filter before encountering the elements. An electric fan will draw the air through the duct when the automobile is operating at low velocities or when above normal power outputs are required. The tube exterior heat transfer coefficient is based on that for a cylinder in cross flow and the internal heat transfer is for fully developed turbulent flow. The bulk temperature of the air DEPT. AUTOMOBILE ENGG-TOCE

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CRYOCAR is assumed to decrease across each tube row as determined from energy conservation and the pressure drop is determined for the whole tube bank. The heat transfer calculations also account for N2 pressure drop and variations in its thermodynamic properties in the tube elements. Some of the important phenomena not considered at this stage of analysis were the effects of transient LN2 flow rates, start up, frost accumulation, tube fins, and axial thermal conduction. The formation of rime ice is highly probable. The atmospheric moisture will be removed relatively quickly as the ambient air is chilled over the first few tube rows, leaving extremely dry air to warm up the coldest parts at the rear of the heat exchanger where the LN2 enters. Surface coatings such as Teflon can be used to inhibit ice buildup and active measures for vibrating the tube elements may also be applied. The LN2 viscous pressure drop would be about 0.05 MPa, which is easily compensated for with the cryogen pump. The electric fan would require approximately 1.5 kW to accelerate the air and overcome the 400 Pa pressure drop through the heat exchanger if the vehicle were standing still. Since each element is 0.76 kg, the total tubing mass would be 19 kg. If the same mass was added by the manifolds and duct then the net mass of the heat exchanger would be less than 40 kg. When operating on a typical California day, it is expected that this over-designed cryogen vaporizer will readily heat the LN2 up to ambient temperature without any appreciable icing.

CHAPTER 5 DEPT. AUTOMOBILE ENGG-TOCE

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PRINCIPLE OF OPERARTION  LN2 at –320oF (-196oC) is pressurized and then vaporized in a heat exchanger by 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.  Liquid N2 passing through the primary heat exchanger quickly reaches its boiling point.  The N2 expands to a gas with a pressure of 150 KPa.  The pressurized N2 gas drives the motor.  The only exhaust is nitrogen, which is major constituent of our atmosphere.  Heat Energy + N2(l) → N2(g) + Work Done Hence, there is no pollution produced by running this car.

CHAPTER 6 POWER CYCLE (Rankine Cycle) DEPT. AUTOMOBILE ENGG-TOCE

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Fig 8 Graph of Temp vs Entropy There are many thermodynamic cycles available for utilizing the thermal potential of liquid nitrogen. These range from the Brayton cycle, to using two- and even three-fluid topping cycles, to employing a hydrocarbon-fueled boiler for superheating beyond atmospheric temperatures. The easiest to implement, however, and the one chosen for this study, is shown above. This system uses an open Rankine cycle. 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 vapour. Process 3-4: The dry saturated vapour expands through a turbine, generating power. This decreases the temperature and pressure of the vapour, and some condensation may occur. Process 4-1: The wet vapour then enters a condenser where it is condensed at a constant pressure to become a saturated liquid.

CHAPTER 7 EFFICIENCY DEPT. AUTOMOBILE ENGG-TOCE

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CRYOCAR  The first LN2 car could travel 79 miles (127.58 km) on a full 24 gallon (90 liter) tank of liquid nitrogen going 32 Kmph.  Its maximum speed was over 56 Kmph. After further researches, the efficiency has improved as follows  Power : 78KW or 104.5bhp @ 97Kmph  400 Liters (106 gallon) gives a mileage of 560Km and weighs 280Kg  Operating Cost is around 2.4cents per Km( Re 1 per Km)

CHAPTER 8 ADVANTAGES 8.1 Compare to Electric Cars: Studies indicate that liquid nitrogen automobiles will have significant performance and environmental advantages over electric vehicles. A liquid nitrogen car with a 60-gallon tank will have a potential range of up to 200 miles, or more than twice that of a typical electric car. Furthermore, a liquid nitrogen car will be much lighter and refilling its tank will take only 10-15 minutes, rather than the several hours required by most electric car concepts. Motorists will fuel up at filling stations very similar to today's gasoline stations. DEPT. AUTOMOBILE ENGG-TOCE

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CRYOCAR A cryogenic car could have three times the range of an electric car of the same weight and no battery disposal concerns. When liquid nitrogen is manufactured in large quantities, the operating cost per mile of a liquid nitrogen car will not only be less than that of an electric car but will actually be competitive with that of a gasoline car.

8.2 As Compared to Fossil Fuels: The process to manufacture liquid nitrogen in large quantities can be environmentally 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. 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.

CHAPTER 9 TECHNICAL ISSUES  The N2 passing through the tubes of the heat exchanger is so cold that the moisture in the surrounding air would condense on the outside of the tubes, obstructing the air flow.  There's the safety issue. Should a nitrogen car be kept in a poorly ventilated space and, if the Nitrogen leaks off, it could prove fatal.  Turning N2 gas into a liquid requires a lot of energy. So while cryogenic cars have zero emissions, they rely on energy produced at emission generating power plants.

PROBABLE SOLUTIONS  A tube within a tube design.  N2 passes back and forth inside a set of three nested tubes. DEPT. AUTOMOBILE ENGG-TOCE

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CRYOCAR  By the time it reaches the outermost tubes, the N2 is warm enough that the exterior wall of the tube remains above the freezing point of water.  Route the exhaust from the fossil fuel power plants through cryogenic plants, so that the pollutants and the greenhouse gases could be condensed for later disposal

CHAPTER 10 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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CHAPTER 11 REFERENCES [1] “LN2000”, University of Washington Research Team, Sept. 18, 2007 [2] “Liquid Nitrogen”, Wikipedia Online Encyclopedia. [3] Proceeding of 18th International Cryogenic Engineering Conference (Edited by K.G Narayankhedhar, Narosa Publishing House) [4] AICTE-ISTE Short term Programme on contribution to technology development from Space Research. [5] “Cryogenic Chilling and Freezing”, BOC Gases. [6] “Cryogenic Paint Removal”, Sig Attilio Bernasconi [7] “Processes and Materials of Manufacture” , R.A. LINDBERG DEPT. AUTOMOBILE ENGG-TOCE

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