Quasi-Isothermal Expansion Engines for Liquid Nitrogen Automotive Propulsion

Abstract

An automotive propulsion concept is presented which utilizes liquid nitrogen as the working fluid for an open Rankine cycle. Ambient heat exchangers are used to power an engine that is configured to maximize heat transfer during the expansion stroke. If sufficient heat input during the expansion process can be realized then this cryogenic propulsive system would provide greater automotive ranges and lower operating costs than those of electric vehicles currently being considered for mass production.The feasibility of meeting this engineering challenge has been evaluated and several means of achieving quasi-isothermal expansion are discussed. ABSTRACTAn automotive propulsion concept is presented which utilizes liquid nitrogen as the working fluid for an open Rankine cycle. Ambient heat exchangers are used to power an engine that is configured to maximize heat transfer during the expansion stroke. If sufficient heat input during the expansion process can be realized then this cryogenic propulsive system would provide greater automotive ranges and lower operating costs than those of electric vehicles currently being considered for mass production.The feasibility of meeting this engineering challenge has been evaluated and several means of achieving quasi-isothermal expansion are discussed.

Development of a hybrid pneumatic-power vehicle

“…From the late 1990s, numerous studies [2][3][4][5][6][7] have considered the high-efficiency energy-conversion system for liquid nitrogen vehicles. Up to now, there are no related documents concerning the research and development of a hybrid pneumatic power system.…”

Energy-saving hybrid vehicle using a pneumatic-power system

“…Furthermore, because of its long range, the air-powered vehicle can satisfy the demands of many drivers. In 1997, Texas University and Washington State University [7,8] jointly developed a liquid-nitrogen powered vehicle. The operating principle is that liquid nitrogen (LN 2 ) can generate a quasi-isothermal expansion process and subsequently yield g motor mechanical efficiency of pneumatic motor g system efficiency of the system g total thermal efficiency of the overall system the necessary power.…”

High Efficiency Energy Conversion Systems for Liquid Nitrogen Automobiles

“…Prior investigations have shown that reasonable piston and cylinder head geometries having high surface-to-volume ratios can be used to enhance heat transfer during expansion, resulting in potential net work output of approximately 85% isothermal. 10 An alternative means of approaching isothermal operation is to use multiple expansions with intermediate reheats. Three expansions with two reheats result in a net work output of 80-85% isothermal; such triple expansion engines were applied quite successfully in the early part of the twentieth century for steamboat propulsion.…”

“…4,5,10 Even though these specific energy values are superior to those of most electrochemical batteries, the energy density of LN 2 is at best 70 W-hr/l when used in an isothermal expansion process, which results in a 350 liter (90 gal) onboard storage vessel being needed to provide a vehicle with a range comparable to internal combustion engines. Even though this is not a prohibitively large "fuel" tank, increasing the effective energy density of the LN 2 by using more complex power cycles may be warranted in applications where minimal energy storage volume, zero emission and spark-free operation are required.…”