AirСar CAES-Compressed Air Energy Source-Compendium

Abstract

This paper is a re evaluation of CAES Compressed Air Energy Source. CAES is not new, experimental air car compressed air propulsion vehicles appeared in early 1900’s, and are currently exemplified by the India Tata Motors AirCar MiniCat based on the French MDI Motor Development International AirCar. (see Ulf Bossel, European Fuel Cell Forum) This study focuses on compressed air potential pressure specific energy density and specific power, ideal Global thermodynamic cycle efficiency, US EPA 23 cycle urban driving test schedule overall drive train ideal efficiency and vehicle ideal range. CAES analysis is unique because compression and expansion cycles are remotely linked solely by ambient atmosphere e.g., compression occurs in a stationary device while expansion takes place in a mobile vehicle. Therefore, ideal thermodynamic compression and/or expansion cycles can be treated independently and linked as isothermal entities e.g., both cycles are in fact separate ideal complete compression and/or complete expansion cycles without (TDC) top dead center piston clearance with isothermal ambient temperature compressed air storage. Further, CAES potential pressure energy density and power density are comparable to electro-chemical energy sources on a Ragone chart, e.g., CAES specific energy density and specific power based solely on stored pressure energy potential are similar to the Pb-Acid battery. However, modern forms of multi stage expansion air motors with heat exchangers between stages extract additional thermal energy directly from ambient air to increase vehicle range by a factor of ~ 6 with a four stage expansion motor. To minimize road-load energy consumption air powered vehicles are characterized by low curb (empty) vehicle mass and low speed urban traffic. Based on Tata AirCar design specifications, comparative theoretical driving range tests were simulated with the 23 cycle US EPA Urban (City) driving schedule and a modified low speed 23 cycle Urban schedule suitable for India. We concluded modern multi stage air car propulsion may find applications in temperate zones, particularly highly congested pedestrian trafficked city streets and retirement communities such as Sun City, AZ, India [5a-19a]