PV2007_4702.pdf

5th International Energy Conversion Engineering Conference and Exhibit (IECEC)

25 - 27 June 2007, St. Louis, Missouri

AIAA 2007-4702

Stirling Engine Research at the Army Research Laboratory

Thomas F. Podlesak 1

U.S. Army Research Laboratory, Adelphi, MD, 20783

The U. S. Army Research Laboratory has recently conducted experiments with a 1 kW

Stirling engine generator-battery hybrid power system in its Small Engine Laboratory. The

Stirling engine system, manufactured by Infinia of Kennewick, WA, has been used to power

what is termed a picogrid. This device, whose name is designated as a micro microgrid, is a

benchtop breadboard of a typical small scale AC power distribution system. The work is

being primarily done for the Power Generation Branch of the Army’s Communication-

Electronics Command, which has responsibility for field power generation. The Army

interest in Stirling engines is in their inherently quiet operation, a valuable element for

military applications. The picogrid consists of four independently switchable electrical loads

connected line to neutral across a three wire 220/110 VAC service. Three of the loads consist

of lump components (resistors, inductors, capacitors) which may be configured to represent

any theoretical load. The fourth load plugs into a standard 110 VAC convenience outlet and

is intended for actual loads that the Army might use in the field, such as hand held electric

power tools. Each load is switchable via a relay, which allows loads to be connected and

disconnected in a convenient manner. The overall objective is to study how well the Stirling

engine-battery hybrid follows and responds to varying loads and to compare this capability

to more conventional internal combustion engine driven generators. The hybrid

configuration was selected to allow the Stirling engine to provide steady state power and for

the batteries to provide peaking power and transient response. The current batteries are

conventional lead acid. ARL has an extensive research effort in advanced batteries and

more efficient batteries will be evaluated as possible replacements for the current lead acid

batteries.

Nomenclature

= frequency of power piston

= engine power

= pressure

= power piston displacement

I. Introduction

The U.S Army has extensive need for electrical power generation. This extends from power for devices carried

by individual soldiers to power for large fixed and mobile installations. The soldier carried devices are usually low

powered and are usually battery powered. Larger users usually rely on engine driven generators. The recent trend

has been for ever increasing power demand as more and more sophisticated devices of all types are fielded. A

critical range of power generation is in the hundreds of watts to low kilowatt range. This is an awkward range, too

large for batteries and too small for conventional generators. Small generator based power sources have been

proposed for this power range. Further, operations in this power range tend to be of a stealth nature, so a power

source with low telltale emissions, usually referred to as signatures, is of great value. Of all of the signatures, which

can include thermal and chemical species, acoustic noise is perhaps the easiest detectable and the most desired to be

controlled. Given these desired characteristics, Stirling engines are leading candidates for this application. The

Army Research Laboratory has embarked on a program to assess the application of Stirling engines to military

applications. It should be noted that one often cited advantage of Stirling engines, that being flexibility of fuel

types, is not considered an advantage for Army applications, in that the Army wishes to operate all of its fuel

consuming devices from one type of fuel, usually JP-8, the militarized version of Jet A jet fuel, and will go to great

1 Electronics Engineer, Directed Energy Branch, 2800 Powder Mill Road, Adelphi, MD , ATTN: AMSRD-ARL-SE-

American Institute of Aeronautics and Astronautics

This material is declared a work of the U.S. Government and is not subject to copyright protection in the United States.

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