22-01-2013, 09:46 AM
Seminar Report On: - CRYOCAR
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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.
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.
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.
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.
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.
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.