Revolutionary proposal: The power take-off occurs on both the exhaust gases (2, 3) as well as electric (10, 4) with a linear alternator. The engine had a supercharger too (5). The proposal was never realized.
The first plant with two engines and a turbo-generator was built in 1938. The test results were consistent with the calculated values.
The experience with the two G30 engines have been integrated in the construction of the GS30. This engine had an output of 1000 HP. The outbreak of WW2 hampered the development of the work.
This patent shows the basis for the successful Pescara turbine drives. Outward compressing was replaced by inward compressing. This means that the scavenging air was compressed during inward stroke. This revolutionary design - combined with a mass-neutral piston synchronization - was a commercial breakthrough after WW2.
The outward compressing Sulzer engine had twice the size of a GS30 but the same power output. The one and only sold equipment had to be withdrawn, however, because the promised power output could not be reached.
On Navy order, 5 different outward compressing prototypes were built to drive a jet turbine.
The Pescara patent protection required an outward compressing and modifications in gas exchange.
The first 1250 HP prototype, built at SIGMA Lyon, on the test bench. The high expectations were met and soon a couple of engines were sold.
First locomotive 040-GA-1 "La Pescara" with a free-piston gas turbine system Pescara. 1959-61 followed by two other Renault engines. In Russia, "Kharkov Locomotive Works," also bilt several locomotives with copied Pescara drives.
1952 - 1956: French Navy ordered 20 minesweepers that were fitted with a Pescara Free Piston Turbine Propulsion:
M701 Sirius (1952-1971), M702 Rigel (1953-1974), M703 Antares (1953-1981), M704 Algol (1953-1976), M705 Aldébaran (1953-1970), M706 Régulus (1952-1974), M707 Véga (1953-1981), M708 Castor (1953-1973), M709 Pollux (1953-1970), M740 Cassiopé (1953-1976), M741 Eridan renommé Aldébaran en 1977 (1953-1979), M742 Orion (1953-1970), M743 Sagittaire (1953-1979), M744 Achernar (1953-1970), M745 Procyon (1953-1970), M710 Pégase (1955-1974) M750 Bellatrix (1955-1974), M751 Denébola (1955-1974), M752 Centaure (1955-1970), M753 Fomalhaut (1955-1970).
Ford built a few prototypes, which were heavily inspired by the construction of Pescara. The first engine had 16 HP, this was followed by some 100 hp variants, and finally a version with 160 hp, which was fitted to a tractor.
1967 End of SIGMA (Company flyer)
After 1962 retirement of the Pescara chief engineer Robert Huber, the decline of free-piston technology began. There were several reasons:
- The slow-speed diesel engines meanwhile equalized the efficiency of free-piston gas turbines.
- The Pescara GS34 engine - an improved prototype with a technical level of 1939 - was not developed further. The engine was a victim of its own success, a succeeding model was never developed.
- Various successors (Stabine, Stelzer, Jarret, copycats) had conceptual or technical problems and damaged the reputation of the free-piston engines very much.
1969 Stabine SA, Le Creusot, Prototype
The pomised power output of some 15000 KW was never achieved. More than 150 Mio French Francs were invested, then the company went bancrupt.
This was a technical suicide for the free piston technology, that was developed by Robert Huber of "Bureau Technique Pescara" with 35 years of experience (1927 - 1962).
In relation to power, the moving mass of the Stabine engine was more than twice as heavy compared with the GS34. Accordingly, the piston acceleration was too low and thus the thermal efficiency was not achieved.
Free-Piston Diesel Engine Timing and Control
Towards Electronic Cam- and Crankshaft
Dynamics and Control of a Free-Piston Diesel Engine
Tor A. Johansen, Olav Egeland, Erling Aa. Johannessen and Rolf Kvamsdal