Turbo-compound engine

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The Napier Nomad engine. The power-recovery turbine sits underneath a two-stroke diesel engine. Napier Nomad.jpg
The Napier Nomad engine. The power-recovery turbine sits underneath a two-stroke diesel engine.

A turbo-compound engine is a reciprocating engine that employs a turbine to recover energy from the exhaust gases. Instead of using that energy to drive a turbocharger as found in many high-power aircraft engines, the energy is instead sent to the output shaft to increase the total power delivered by the engine. The turbine is usually mechanically connected to the crankshaft, as on the Wright R-3350 Duplex-Cyclone, but electric and hydraulic power recovery systems have been investigated as well.

Contents

As this recovery process does not increase fuel consumption, it has the effect of reducing the specific fuel consumption, the ratio of fuel use to power. [1] Turbo-compounding was used for commercial airliners and similar long-range, long-endurance roles before the introduction of turbojet engines. Examples using the Duplex-Cyclone include the Douglas DC-7B and Lockheed L-1049 Super Constellation, while other designs did not see production use.

Concept

Most piston engines produce a hot exhaust that still contains considerable undeveloped energy that could be used for propulsion if extracted. A turbine is often used to extract energy from such a stream of gases. A conventional gas turbine is fed high-pressure, high-velocity air, extracts energy from it, and leaves as a lower-pressure, slower-moving stream. This action has the side-effect of increasing the upstream pressure, which makes it undesirable for use with a piston engine as it increases the back-pressure in the engine, which decreases scavenging of the exhaust gas from the cylinders and thereby lowers the efficiency of the piston portion of a compound engine. [2]

Through the late 1930s and early 1940s one solution to this problem was the introduction of "jet stack" exhaust manifolds. These were simply short sections of metal pipe attached to the exhaust ports, shaped so that they would interact with the airstream to produce a jet of air that produced forward thrust. Another World War II introduction was the use of the Meredith effect to recover heat from the radiator system to provide additional thrust.

By the late-war era, turbine development had improved dramatically and led to a new turbine design known as the "blowdown turbine" or "power-recovery turbine". This design extracts energy from the momentum of the moving exhaust, but does not appreciably increase back-pressure. This means it does not have the undesirable effects of conventional designs when connected to the exhaust of a piston engine, and a number of manufacturers began studying the design.

History

Wright R-3350 Duplex-Cyclone Turbo-Compound radial engine. Wright R-3350 Cyclone Engine 1.jpg
Wright R-3350 Duplex-Cyclone Turbo-Compound radial engine.

The first aircraft engine to be tested with a power-recovery turbine was the Rolls-Royce Crecy. This was used primarily to drive a geared centrifugal supercharger, although it was also coupled to the crankshaft and gave an extra 15 to 35 percent fuel economy. [3]

Blowdown turbines became relatively common features in the late- and post-war era, especially for engines designed for long overwater flights. Turbo-compounding was used on several airplane engines after World War II, including the Napier Nomad [4] [5] and the Wright R-3350. [6] [7] The exhaust restriction imparted by the three blowdown turbines used on the Wright R-3350 is equal to a well-designed jet stack system used on a conventional radial engine, while recovering about 550 hp (410 kW) at METO (maximum continuous except for take-off) power. [2] In the case of the R-3350, maintenance crews sometimes nicknamed the turbine the parts recovery turbine due to its negative effect on engine reliability. Turbo-compound versions of the Napier Deltic, Rolls-Royce Crecy, Rolls-Royce Griffon, and Allison V-1710 were constructed but none was developed beyond the prototype stage. It was realized in many cases the power produced by the simple turbine was approaching that of the enormously complex and maintenance-intensive piston engine to which it was attached. As a result, turbo-compound aero engines were soon supplanted by turboprop and turbojet engines.

Some modern heavy truck diesel manufacturers have incorporated turbo-compounding into their designs. Examples include the Detroit Diesel DD15 [8] [9] and Scania [10] in production from 1991. [11] [ clarification needed ]

Starting with the 2014 season, Formula 1 switched to a new 1.6 liter turbocharged V6 formula that uses turbo-compounding. The engines use a single turbocharger that is connected to an electric motor/generator called the MGU-H. The MGU-H uses a turbine to drive a generator, converting waste heat from the exhaust into electrical energy that is either stored in a battery or sent directly to an electric motor in the car's powertrain.

List of types

Diagram showing a true turbo-compound at the bottom, and a gas turbine loosely coupled to a piston engine at the top NomadSchematic 185kBpng360kB.png
Diagram showing a true turbo-compound at the bottom, and a gas turbine loosely coupled to a piston engine at the top

See also

Related Research Articles

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In an internal combustion engine, a turbocharger is a forced induction device that is powered by the flow of exhaust gases. It uses this energy to compress the intake gas, forcing more air into the engine in order to produce more power for a given displacement.

<span class="mw-page-title-main">Gas turbine</span> Type of internal and continuous combustion engine

A gas turbine, also called a combustion turbine, is a type of continuous flow internal combustion engine. The main parts common to all gas turbine engines form the power-producing part and are, in the direction of flow:

<span class="mw-page-title-main">Four-stroke engine</span> Internal combustion engine type

A four-strokeengine is an internal combustion (IC) engine in which the piston completes four separate strokes while turning the crankshaft. A stroke refers to the full travel of the piston along the cylinder, in either direction. The four separate strokes are termed:

  1. Intake: Also known as induction or suction. This stroke of the piston begins at top dead center (T.D.C.) and ends at bottom dead center (B.D.C.). In this stroke the intake valve must be in the open position while the piston pulls an air-fuel mixture into the cylinder by producing a partial vacuum in the cylinder through its downward motion.
  2. Compression: This stroke begins at B.D.C, or just at the end of the suction stroke, and ends at T.D.C. In this stroke the piston compresses the air-fuel mixture in preparation for ignition during the power stroke (below). Both the intake and exhaust valves are closed during this stage.
  3. Combustion: Also known as power or ignition. This is the start of the second revolution of the four stroke cycle. At this point the crankshaft has completed a full 360 degree revolution. While the piston is at T.D.C. the compressed air-fuel mixture is ignited by a spark plug or by heat generated by high compression, forcefully returning the piston to B.D.C. This stroke produces mechanical work from the engine to turn the crankshaft.
  4. Exhaust: Also known as outlet. During the exhaust stroke, the piston, once again, returns from B.D.C. to T.D.C. while the exhaust valve is open. This action expels the spent air-fuel mixture through the exhaust port.
<span class="mw-page-title-main">Napier Nomad</span> British diesel aircraft engine

The Napier Nomad is a British diesel aircraft engine designed and built by Napier & Son in 1949. They combined a piston engine with a turbine to recover energy from the exhaust and thereby improve fuel economy. Two versions were tested, the complex Nomad I which used two propellers, each driven by the mechanically independent stages, and the Nomad II, using the turbo-compound principle, coupled the two parts to drive a single propeller. The Nomad II had the lowest specific fuel consumption figures seen up to that time. Despite this the Nomad project was cancelled in 1955 having spent £5.1 million on development, as most interest had passed to turboprop designs.

<span class="mw-page-title-main">Wright R-3350 Duplex-Cyclone</span> 1937 18-cylinder radial piston engine family by Wright

The Wright R-3350 Duplex-Cyclone is an American twin-row, supercharged, air-cooled, radial aircraft engine with 18 cylinders displacing nearly 3,350 cubic inches (54.9 L). Power ranged from 2,200 to over 3,700 hp, depending on the model. Developed before World War II, the R-3350's design required a long time to mature before finally being used to power the Boeing B-29 Superfortress. After the war, the engine had matured sufficiently to become a major civilian airliner design, notably in its turbo-compound forms, and was used in the Lockheed L-1049 Super Constellation airliners into the 1950s. The engine is commonly used on Hawker Sea Fury and Grumman F8F Bearcat Unlimited Class Racers at the Reno Air Races. Its main rival was the 4,360 in3 (71.4 L), 4,300 hp (3,200 kW) Pratt & Whitney R-4360 Wasp Major, first run some seven years after the Duplex-Cyclone's beginnings.

<span class="mw-page-title-main">Garrett Motion</span> American industrial company

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<span class="mw-page-title-main">Ford Power Stroke engine</span> Motor vehicle engine

Power Stroke, also known as Powerstroke or PowerStroke, is the name used by a family of diesel engines for trucks produced by Ford Motor Company and Navistar International for Ford products since 1994. Along with its use in the Ford F-Series, applications include the Ford E-Series, Ford Excursion, and Ford LCF commercial truck. The name was also used for a diesel engine used in South American production of the Ford Ranger.

A wastegate is a valve that controls the flow of exhaust gases to the turbine wheel in a turbocharged engine system.

The anti-lag system (ALS) is a method of reducing turbo lag or effective compression used on turbocharged engines to minimize turbo lag on racing or performance cars. It works by delaying the ignition timing and adding extra fuel to balance an inherent loss in combustion efficiency with increased pressure at the charging side of the turbo. This is achieved as an excess amount of fuel/air mixture escapes through the exhaust valves and combusts in the hot exhaust manifold spooling the turbocharger creating higher usable pressure.

<span class="mw-page-title-main">Rolls-Royce Crecy</span> 1940s British piston aircraft engine

The Rolls-Royce Crecy was a British experimental two-stroke, 90-degree, V12, liquid-cooled aero-engine of 1,593.4 cu.in capacity, featuring sleeve valves and direct petrol injection. Initially intended for a high-speed "sprint" interceptor fighter, the Crecy was later seen as an economical high-altitude long-range powerplant. Developed between 1941 and 1946, it was among the most advanced two-stroke aero-engines ever built. The engine never reached flight trials and the project was cancelled in December 1945, overtaken by the progress of jet engine development.

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The Shvetsov ASh-73 was an 18-cylinder, air-cooled, radial aircraft engine produced between 1947 and 1957 in the Soviet Union. It was primarily used as the powerplant for the Tupolev Tu-4 heavy bomber, an unlicensed, reverse engineered copy of the American Boeing B-29 Superfortress.

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An electric turbo-compound (ETC) system is defined where a turbine coupled to a generator (turbogenerator) is located in the exhaust gas flow of a reciprocating engine to harvest waste heat energy and convert it into electrical power.

<span class="mw-page-title-main">Mercedes V6 Hybrid Formula One engine</span> Motor vehicle engine

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References

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  2. 1 2 Facts about the Wright Turbo Compound (PDF). Wood Ridge New Jersey: Curtiss-Wright Corporation:Wright Aeronautical Division. October 1956. Archived from the original (PDF) on 16 February 2010. Retrieved 19 February 2016.
  3. "Rolls-Royce and the Sleeve Valve" (PDF). New Zealand Rolls-Royce & Bentley Club Inc (7–3): 15. 2007. Archived from the original (PDF) on 6 December 2010.
  4. Gunston, Bill (30 April 1954). "Napier Nomad: An engine of outstanding efficiency". Flight : 543–551. Archived from the original (PDF) on 5 March 2016. Retrieved 19 February 2010.
  5. E. E. Chatterton (22 April 1954). "Napier Diesels: An RAeS Lecture" (PDF). Flight : 552. Retrieved 19 February 2010.
  6. "Ten Ideas That Failed: 2 Turbo-compound Piston Engine" (PDF). Flight . 16 December 2003. Retrieved 19 February 2010.
  7. "Super Survivor" (PDF). Flight . 18 June 1997. Retrieved 19 February 2010. in its hey-day, the Connie was often called the world's best tri-motor
  8. "DD15" (video). Detroit Diesel.
  9. "DD15 Brochure" (PDF). Detroit Diesel.
  10. "Scania Turbocompound". Scania Group. Archived from the original on 30 January 2010.
  11. "Scania produces 4 ECO-point engine from Oct 2001". Scania Group. Archived from the original on 7 August 2011. With 440 hp, the new version of Scania's 12-litre turbocompound engine is suitable for Alpine terrain, as well as normal European long-haul and construction operations.
  12. "The Turbo Compounding Boost". 2007.