In Sterling-cycle heat engine, pneumatic system is used to drive displacer/regenerator, eliminating mechanical linkages and valves

Higa, W. H.

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(b)	 (c) (d) 
Cold Char 
Figure 1. Simplified-Heat-Engine Cycle
December 1975	 B75-10334 
•	 NASA TECH BRIEF 
NASA Pasadena Office 
NASA Tech Briefs announce new technology derived from the U.S. space program. They are issued to encourage 
commercial application. Tech Briefs are available on a subscription basis from the National Technical Information 
Service, Springfield, Virginia 22151. Requests for individual copes or questions relating to the Tech Brief program may 
be directed to the Technology Utilization Office, NASA, Code KT, Washington, D.C. 20546. 
Simplified Heat Engine 
In a new Sterling-cycle heat engine, heat absorbed 
from an external source expands a gas that acts on a 
piston to perform work. The engine is shown in Figure 
1; an interesting feature is the pneumatic system used 
to drive the displacer/regenerator, thus eliminating 
mechanical linkages and valves. The essential features 
are a "constant-pressure" chamber (P 0) the displacer/ 
regenerator, and a drive piston. 
The operation and features of the engine can be 
best understood by following through a single cycle. 
In Figure 1(a), the piston and the displacer are both at 
their lowest points, and most of the working gas is in 
the area referred to as the cold chamber. The 
working-gas pressure, P 1, is less than P0. These 
conditions correspond to point (a) on the indicator 
diagram of Figure 2. 
A flywheel causes the crankshaft to continue to 
rotate, move the piston upward, and begin compress-
ing the working fluid. At some point, pressure P1
exceeds P 0
 [(b) in Figure 2], and the displacer is 
forced upward into chamber P 0
 as shown in Figure 
1(b). (In practice, the volume of chamber P 0
 is much 
larger than the volume of the working-gas chamber so 
that P0
 remains relatively constant despite the piston 
motion.) 
As the porous displacer moves upward, gas is 
displaced from the cold chamber to the hot chamber, 
absorbing some previously deposited heat as it passes 
through the displacer/regenerator. The working fluid 
absorbs further heat from the heat-transfer manifold. 
This continues until the piston and the displacer are 
at their uppermost positions [Figure 1(c) and point (c) 
in Figure 2]. 
At this point, temperature and pressure are at a 
maximum, and the working gas will expand and push 
the drive piston downward, which applies a rotational 
force to the crankshaft and flywheel. The flywheel 
inertia causes the piston to continue past the point 
Constant-Pressur 
¶Chamber
Cold 
ChambE 
Heat 
Transfer 
Manifold 
Displaceri 
Regenerato Drive 
Piston 
Flywheel and 
Crankshaft 
(a)
(continued overleaf) 
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https://ntrs.nasa.gov/search.jsp?R=19750000334 2020-03-19T20:18:50+00:00Z
0 
c(TH) 
(5 
0 
C 
0 
0 
a) 
(0 
G0 
a) 
0
0 
_d 
I	 I 
I	 I 
I	 I 
Volume of Working Gas (V) 
Figure 2. Pressure/Volume Indicator Diagram for Heat Engine 
where P1 = P0. The continued expansion and the 
resulting cooling make P 1
 less than P0 [Figure 1(d) 
and point (d) on Figure 2], and the displacer/ 
regenerator is forced downward. 
While the displacer was in the cold chamber, its 
temperature was lowered somewhat by the cooling 
manifold; at the same time, the working gas was 
heated. Thus, as the gas passes back through the 
regenerator and into the cold chamber, some of its 
heat is absorbed by the regenerator. The gas is further 
cooled in the cold chamber. When the piston reaches 
its lowest point, the cycle is back at the state indicated 
in Figure 1(a) and point (a) of Figure 2. 
The timing of the pressure variations and of the 
piston and displacer motions is obtained by selecting 
the appropriate flywheel moment of inertia, the 
amount of working gas, pressure P 0, and the 
difference between chamber temperatures. As can be 
seen from Figure 2, heat absorbed by the gas at a high 
temperature results in expansion and yields work 
equal to the area of path abcda. Typical conditions 
are TH = 800 K (9800 F), TC = 370 K (210° F), and P0 
= 1.38x106 N/rn 2
 (200 psi). The displacer/regenerator 
can be packed with steel wool or can be a 
solid-cylinder displacer with the regenerator outside 
the engine housing.
The engine is only moderately efficient, but it could 
be particularly useful with nuclear reactors where 
there might be large quantities of otherwise-wasted 
heat and where the reduced maintenance is impor-
tant. With only a few modifications, the engine could 
also be used as a refrigerator. 
Note: 
Requests for further information may be directed 
to:
Technology Utilization Officer 
NASA Pasadena Office 
4800 Oak Grove Drive 
Pasadena, California 91103 
Reference: TSP75- 10334 
Patent status: 
This invention is owned by NASA, and a patent 
application has been filed. Inquiries concerning 
nonexclusive or exclusive license for its commercial 
development should be addressed to: 
Patent Counsel 
NASA Pasadena Office 
4800 Oak Grove Drive 
Pasadena, California 91103 
Source: Walter H. Higa of 
Caltech/JPL 
(NPO-13613)
. 
. 
B75-10334	 Category: 07 (Machinery)


Simplified heat engine

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