| Definition
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 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 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. HISTORY 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
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