During his time there, thousands of free-piston engines had been sold.

Huber continued to work on free-piston engines until at least 1967.

Robert Huber has about 40 patents related to free-piston engines.

The first successful application of the free-piston engine concept was as air compressors.

Eighteen types of free-piston engine were built and tested.

In the 21st century, research continues into free-piston engines and patents have been published in many countries.

A review of free-piston engine history and applications.

The free-piston engines provided some advantages over conventional technology, including compactness and a vibration-free design.

The free-piston engine linear generators can be divided in 3 subsystems:

Free-piston engines could be used to generate electricity as efficiently as, and less expensively than, fuel cells.

A number of patents for linear compressors powered by free-piston engines were issued in the 20th century, including:

The operational characteristics of free-piston engines differ from those of conventional, crankshaft engines.

In the UK, Newcastle University is undertaking research into free-piston engines.

The free-piston engine is usually restricted to the two-stroke operating principle, since a power stroke is required every fore-and-aft cycle.

A new kind of the free-piston engine, a Free-piston linear generator is being developed by the German aerospace center.

The free-piston engine was patented in 1934 by Raul Pateras Pescara.

This system was derived from Raúl Pateras Pescara's work on free-piston engines in the 1930s.

A Free-piston gas generator is a free-piston engine whose exhaust is used to power a gas turbine.

The free-piston engine is further well suited for homogeneous charge compression ignition (HCCI) operation.

The modern free-piston engine was proposed by R.P. Pescara and the original application was a single piston air compressor.

A variation on the opposed-piston engine is the free-piston engine, which was patented in 1934 by Raúl Pateras de Pescara.

In 1937, he founded Alan Muntz & Co. Ltd to develop the Pescara free-piston engine system and other inventions.

The basic configuration of free-piston engines is commonly known as single piston, dual piston or opposed pistons, referring to the number of combustion cylinders.

These first generation free-piston engines were without exception opposed piston engines, in which the two pistons were mechanically linked to ensure symmetric motion.

The main difference is due to the piston motion not being restricted by a crankshaft in the free-piston engine, leading to the potentially valuable feature of variable compression ratio.