Engine Types

1903 National Free Piston Engine Co
1903 National Free Piston Engine Co
1903 National Free Piston Engine Company Limited, USA

First patent filed for a free-piston engine

Download Patent

The idea behind this invention: hammers and tunnel drilling machines, driven by the vibration of an oscillating mass

Diesel Hammer
Diesel Hammer
From about 1935, the well-known diesel hammer (diesel pile) was developed

Diesel Hammer
Diesel Hammer
Diesel Hammer Function

Warsop Benjo Power Rammer
Delmag Dieselhammer
Delmag Dieselhammer
The modern world would be inconceivable without the famous Delmag Diesel Hammers

www.delmag.com 

Usually, free-piston engines were invented or provided for a specific purpose. Therefore, they are classified into the following groups and described separately:




Special cases: Harold Kosoff, Frank Stelzer, Jack Horton
Harold Kosoff
Harold Kosoff
1964 Harold Kosoff, USA

Harold Kosoff developed an opposed piston engine in which the pistons are synchronized pneumatically rather than mechanically (Pescara, Junkers).

Download US-Patent

Harold Kosoff
Harold Kosoff
1964 Harold Kosoff, USA

As early as 1964 he had a vision of a linear generator, which powered cars and supplied houses with electricity and heat. The engine was not developed further.

Download Mechanix Illustrated Article

Special cases: Frank Stelzer
Frank Stelzer
Frank Stelzer
1963 Frank Stelzer, DE

Frank Stelzer (1934 - 2007) worked on this engine nearly his entire life, without any commercial success. A first patent was filed in 1963. There is no such first working model known .

Download Patent

Frank Stelzer
Frank Stelzer
1980 Frank Stelzer, Germany

Frank Stelzer's second engine having pistons of various diameters.

Download Patent USA

Stelzermotor
Stelzermotor
One of the numerous engines that were built by Stelzer - typically on mobile base frames. This chassis also gave the engine its necessary "freedom of movement" that it needs because of its inevitable vibrations.

Automotive News 1981

Stelzer Engine
Stelzer Engine

The starter usually consist of a hydraulic chuck, moving the piston back and forth until combustion begins. Then the pressure is released from the chuck and the piston can oscillate freely.

Stelzer built the engines much over square. On the one hand, to keep the vibrations within limits, on the other hand because the stroke was severely limited by reason of this hydraulic starting system.

Stelzer Motor
Stelzer Engine
Stelzer Engine
Lack of accuracy in machining and the use of second hand parts from junk yards were additional reasons why this engine was rarely demonstrated without failure since 1980.

Stelzer Engine
Stelzer Engine
Animation of a Stelzer engine

Special cases: Jack Horton
Jack Horton
Jack Horton
1969 Jack Horton, USA Free-Piston Jet Engine 

Probably the most dangerous free-piston engine ever built. According to an MIT study of 1974 (see below), the information about 80 pounds of thrust at 20 lbs weight is not exaggerated. The generated noise, however, is about 145 decibels and the engine is extremely dangerous in operation.

Jack Horton
Jack Horton
1969 Jack Horton

The engine was originally patented by Charles L. Gahagan, then later built by Jack Horton.

Download Patent

Jack Horton
Jack Horton
1969 Jack Horton

Jack Horton
Jack Horton
Acetylen-oil-air mixture fuel is drawn into pump cylinder on right side. Oil is mixed with air to lubricate moving parts. Acetylen-oil-air mixture (injected in previous stroke) is now being compressed in the power cylinder on the right side.

Jack Horton
Jack Horton
The power stroke:
Acetylen-oil-air mixture is compressed in pump cylinder on right side. On left side, pump cylinder is drawing in acetylen-oil-air mixture. Acetylen-oil-air mixture in power cylinder left is being compressed, as shown right in above figure. 

Jack Horton
Jack Horton
At the end of power stroke, spent gasses enter exhaust chamber. Water injected at this point is turned to steam by heat of exhaust gases, causing greatly increased thrust. Compressed fuel mixture from pump cylinder is now blown into the power cylinder.

Horton Engine Test Run
Jack Horton
Jack Horton

Jack Horton
Jack Horton
1974 MIT Horton Engine Study

Download MIT Study
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