DEPARTMENT OF PRODUCTION TECHNOLOGY
MADRAS INSTITUTE OF TECHNOLOGY
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 only exhaust is nitrogen. The usage of cryogenic fuels has significant advantage over other fuels. Also, factors such as production and storage of nitrogen and pollutants in the exhaust give advantage for the cryogenic fuels.
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. 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. PARTS OF A LIQUID NITROGEN PROPULSION CYCLE
The main parts of a liquid nitrogen propulsion system are:
Cryogen Storage Vessel.
The parts and their functions are discussed in detail below: 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. 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. 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. Expander:
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