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Turbocharging and turbocompounding history

by François Dovat

More than 35% of the energy released by the combustion of the fuel is lost in the exhaust.

On 16 November 1905 Swiss engineer Dr. Alfred Büchi received patent No. 204630 from the Imperial Patent Office of the German Reich for a "combustion machine consisting of a compressor (turbine compressor), a piston engine, and a turbine in sequential arrangement. Between 1909 and 1915 he developed the first turbocharger (below) while he was an engineer in charge of the development of the diesels at Sulzer in Winterthur, Switzerland. One of his goals was to partially recover this energy.

The advantages of this system over mechanical supercharging (crankshaft driven compressor) for altitude operation were quickly recognized so that in 1917 Auguste Rateau fitted it to an aircraft engine. Even if steels resistant to the temperatures of the exhaust gases ejected by the spark ignition engines (> 950°C) were not yet available, as early as 1939 the B17 bombers could be outfitted with General Electric turbochargers, thanks to a jet of cold air projected on the turbine.

At about the same period "turbo-supercharging" (as it was then called) was attempted on marine diesels. In its December 1941 issue the Sulzer Technical Review published the performances obtained with a turbocompound opposed pistons diesel, the 4 ZGA 19, whose specific consumption was 158 g/hp/h at its nominal output of 1370 hp. The large and modern 6 G 18 followed, but these experiments ended soon after WW II because of a staff shortage. The exhaust turbine of these engines was geared on the crankshaft; in this way a "free" power was recovered.

Then, in 1953, the double row radial 18 cylinders Wright Turbocyclone entered in regular service on the Super-Constellation and DC 7. This version of the Cyclone R-3350 was improved by the adjunction of 3 exhaust turbines which transmitted their power to the crankshaft by double gear sets and additional fluid couplings absorbing the vibrations of torsion. Specific fuel consumption went down from 210 to 172 g/hp/h and the power on takeoff increased from 2700 to 3300 hp at 2900 rpm whereas the increase of power in altitude was much higher still. From 1956 on, the commercial non-stop crossing of the Atlantic was thus ensured in both directions.

After the landing in Europe of the four-engined planes coming from New York, each of their engines asked for a supplement of 70 to 80 liters of oil[1 ]. These monsters of 55 liters cubic capacity needed 115/145 high octane gasoline. At launch, they spit out long flames and an enormous cloud of smoke, some cylinders firing before the others in a deafening and harsh sound.[2 ]

However, in 1954 the firm Napier achieved the development of a 2-stroke turbocompound diesel, the Nomad, but it was never produced because the first turbojets competed with it and jet fuel was cheap then. Its axial turbocharger was linked to the propeller shaft by a complex continuously variable transmission (Beier CVT concept, see picture in our CVT file) in power split mode. So, at low revs the turbocharger could be accelerated while at high rpm the excess of power available at the turbine could be returned to the propeller shaft.

Small high speed generator-motors coupled directly the turbocharger shaft will soon allow to obtain a similar operation and to improve the transient response of turbocharged engines (Garett picture below). Nevertheless, we shall only be able to benefit of these electric turbochargers after the advent of the 42 volts systems and starters-generators (3).

Since decades several ships are propelled by turbocompound engines. The residual exhaust heat is then used for the production of hot water in exhaust gas boilers.[4 ]

In road traction, the turbocompounding is only recently operational. The gain of approximately 3% announced in fuel economy seems marginal compared to the 22% obtained on the Cyclone, but it is nevertheless interesting. It has been achieved jointly with a clear improvement of the low end torque, a major increase in power and a noise reduction. Years ago Caterpillar, Cummins, Komatsu and others reported sfc reductions of more than 5% on diesel engines prototypes.

Only 1500 units of the first turbocompound engine marketed by Scania (DTC 11) were manufactured between 1991 and 1997. They are said to have known some troubles due to their electronic fuel injection equipment (EDC). New 6 in line 12 liters of Scania and Volvo (opposite, 470 and 500 hp) seem promised to a better future. The provision of their 2 turbines in series was selected between several alternatives for the reason that it improves the useful rev range of the engine and its transient response. The Volvo compound turbine is of the axial type and is located in line with the 1st turbine driving the compressor, thus avoiding the need for a bended duct.

Below approximately a quarter load, the compound turbine becomes useless; these engines therefore give their best under high loads, when the exhaust gas temperature and pressure are high.

[1] In those years, an oil consumption of around 8 g/hp/h was regarded as normal.

[2] A silent Turbocyclone is exposed at the Deutches Museum in Munich. But with a shorter trip to http://www.enginehistory.org/galleries.htm you'll certainly be in awe front of the beautiful CAD images of the Wright R-3350 TC by Ugo Vicenzi.

[3] http://www.orau.gov/deer/DEER2002/Session8/Hopmann.pdf


[4] It is planned to use this residual heat to vaporize water which will actuate a steam turbine, but the equipments needed are probably too complex for automotive applications.

(© François Dovat)

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Idée & conception © 1999-2011 van Damme Stéphane.

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