27-01-2012, 04:31 PM
A review of free-piston engine history and applications
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Introduction
Extensive use of fossil fuels as an energy source
for both sea and land based transport leads to sig-
nificant amounts of CO2 and other pollutants be-
ing produced. Much research, particularly within
the automotive industry, is being undertaken to de-
velop more environmental friendly fuel chains, and
the fuel cell vehicle stands out as a promising tech-
nology for the future.
Free-piston engine basics
Due to the breadth of the free-piston term, many
engine configurations will fall under this category.
The free-piston term is most commonly used to dis-
Preprint submitted to Elsevier 17 February 2009
tinguish a linear engine from a rotating crankshaft
engine. The piston is ‘free’ because its motion is not
restricted by the position of a rotating crankshaft,
as known from conventional engines, but only deter-
mined by the interaction between the gas and load
forces acting upon it.
The original
R.P. Pescara [2] is usually credited with the inven-
tion of the free-piston engine with his patent dating
from 1928, but other vendors, among others Junkers
in Germany, were also working on free-piston ma-
chinery at this time. Since then, a high number of
patents describing free-piston machinery or related
to such machinery have been published. 1 The orig-
inal Pescara patent describes a single piston spark
ignited air compressor but the patent seeks to pro-
tect a large number of applications utilising the free-
piston principle.
Free-piston engine unique features
The free-piston engine has a number of unique fea-
tures, some give it potential advantages and some
represent challenges that must be overcome for the
free-piston engine to be a realistic alternative to con-
ventional technology.
