23-12-2010, 12:08 PM
Prepared by::BHIMRAO
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INTRODUCTION
The potential of cryogenic energy storage for automotive propulsion as an alternative to the electrochemical batteries for zero-emission vehicles (ZEV).
It is anticipated that use of an inert cryogen, such as liquid nitrogen(LN2), as an energy storage would not pose any environmental burden, and in particular would avoid the issues of heavy metals pollution associated with lead-acid batteries.
CRYOGENIC POWER CYCLE
The cryogen “fuel” is stored in a vacuum jacketed vessel which has appropriate relief valves to safely accommodate boiloff.
A cryopump pressurizes the fluid to a level somewhat above the injection pressure of the expander to make up pressure loss in the heat exchanger system.
Turbines and either rotary or reciprocating fixed-displacement engines are appropriate expanders.
The shaft power from the expander is then readily applied for vehicle propulsion
WARMANT CIRCULATION
A “warmant” fluid is circulated through the expander walls to maintain them at near ambient temperature .
The warmant must be pumped through another heat exchanger system to efficiently conduct ambient heat into the engine.
A quasiisothermal reciprocating expander is proposed for this embodiment and its work output is transmitted to the wheels by means of a conventional transmission.
Under cruising operating conditions the propulsion system would realize an energy density of 245 kJ/kg-LN2 which makes it competitive with the best of lead-acid batteries being used today.
THEORETICAL ANALYSIS OF EXPANDER
The thermodynamic simulation of a reciprocating expander has been developed to examine the impact of various engine design and operational parameters on the LN2 consumption of an ambient powered cryomobile.
Reciprocating engine model
Piston cylinder heat transfer
Piston ring friction
Warmant circulation
Analytical procedure
