Twincharger
Encyclopedia
Twincharger refers to a compound forced induction
system used on some piston-type internal combustion engine
s. It is a combination of an exhaust-driven turbocharger
and an engine-driven supercharger
, each mitigating the weaknesses of the other. A belt-driven supercharger offers exceptional response and low-RPM performance as it has no lag time between the application of throttle and pressurization of the manifold. Combined with a large turbo which would offer unacceptable lag and poor response in the low-RPM range, the proper combination of the two can offer a zero-lag powerband with high torque at lower engine speeds and increased power at the higher end. Twincharging is therefore desirable for small-displacement motors (such as VW's 1.4TSI), especially those with a large operating RPM, since they can take advantage of an artificially broad torque band over a large speed range.
Twincharging does not refer to a twin-turbo
arrangement, but rather when two different kinds of compressors are used.
is connected to a medium- to large-sized turbocharger. The supercharger provides near-instant manifold pressure (eliminating turbo lag, which would otherwise result when the turbocharger is not up to its operating speed). Once the turbocharger has reached operating speed, the supercharger can either continue contributing pressurized air to the turbocharger inlet (yielding elevated intake pressures), or it can be bypassed and mechanically decoupled from the drivetrain
via an electromagnetic clutch
and bypass valve or one-way valve (increasing efficiency of the induction system).
Other series configurations exist where no bypass system is employed and both compressors are in continuous duty. As a result, compounded boost is always produced as the pressure ratios of the two compressors are multiplied, not added. In other words, if a supercharger which produced 10 psi (0.6894757293 bar) (pressure ratio = 1.7) alone blew into a turbocharger which also produced 10psi alone, the resultant manifold pressure would be 27 psi (1.9 bar) (PR=2.8) rather than 20 psi (1.4 bar) (PR=2.3) This form of series twincharging allows for the production of boost pressures that would otherwise be unachievable with other compressor arrangements.
However, the efficiencies of the turbo and supercharger are also multiplied, and since the efficiency of the supercharger is often much lower than that of large turbochargers, this can lead to extremely high manifold temperatures unless very powerful charge cooling is employed. For example, if a Roots blower with an efficiency of 60% blew into a turbocharger with an efficiency of 70%, the overall compression efficiency would be only 42% -- at 2.8 pressure ratio as shown above and 20 °C (68 °F) ambient temperature, this would mean air exiting the turbocharger would be 263 °C (505.4 °F), which is enough to melt most rubber couplers and nearly enough to melt expensive silicone couplers. A large turbocharger producing 27 psi (1.9 bar) by itself, with an adiabatic efficiency around 70%, would only produce 166 °C (330.8 °F). Additionally, the energy cost to drive a supercharger is usually several horsepower, thus if it can either be disconnected electrically (using an electromagnetic clutch such as those used on the VW 1.4TSI or Toyota's 4A-GZE) or allowed to freewheel and vent to the atmosphere, several horsepower can be gained independent of the efficiency gain by switching to one compressor.
Thus, switching the supercharger off at a certain boost or RPM threshold is most desirable, since a large, inexpensive journal bearing turbocharger can be used which will provide more than enough pressure and flow at any RPM for most twincharged motors. However, a smooth switchover can be very difficult to accomplish for non-OEM twincharging applications.
in the 1980s on the Lancia Delta S4
rally car. The idea was also successfully adapted to production road cars by Nissan, in their March Super Turbo
.
Additionally, multiple companies have produced aftermarket
twincharger kits for cars like the Subaru Impreza WRX
, Mini Cooper S, Ford Mustang
, Nissan Skyline GT-R
, Toyota MR2
, as well as the GM 3800 Engine, as in the Pontiac Bonneville
SSEI, Pontiac Grand Prix
GTP, and the Chevrolet Cobalt SS
among others.
The Volkswagen 1.4TSI is a 1400 cc engine that utilizes both turbocharger and supercharger. It produces 170 bhp at 6000 rpm and 240 newton metre from 1500 to 4750 rpm.
(N2O) is mixed with incoming air, providing more oxygen to burn more fuel for high power when a turbocharger is not spinning quickly. This also causes the turbocharger to quickly accelerate, providing more oxygen for combustion, and the N2O flow is reduced accordingly. The expense of both the system itself and the consumable N2O can be significant.
(by means of turbocharging or supercharging), an aftermarket
water injection system can be added to the induction system of both gasoline and diesel internal combustion engines.
Forced induction
Forced induction is the process of compressing air on the intake of an internal combustion engine . A forced induction engine uses a gas compressor to increase the pressure, temperature and density of the air...
system used on some piston-type internal combustion engine
Internal combustion engine
The internal combustion engine is an engine in which the combustion of a fuel occurs with an oxidizer in a combustion chamber. In an internal combustion engine, the expansion of the high-temperature and high -pressure gases produced by combustion apply direct force to some component of the engine...
s. It is a combination of an exhaust-driven turbocharger
Turbocharger
A turbocharger, or turbo , from the Greek "τύρβη" is a centrifugal compressor powered by a turbine that is driven by an engine's exhaust gases. Its benefit lies with the compressor increasing the mass of air entering the engine , thereby resulting in greater performance...
and an engine-driven supercharger
Supercharger
A supercharger is an air compressor used for forced induction of an internal combustion engine.The greater mass flow-rate provides more oxygen to support combustion than would be available in a naturally aspirated engine, which allows more fuel to be burned and more work to be done per cycle,...
, each mitigating the weaknesses of the other. A belt-driven supercharger offers exceptional response and low-RPM performance as it has no lag time between the application of throttle and pressurization of the manifold. Combined with a large turbo which would offer unacceptable lag and poor response in the low-RPM range, the proper combination of the two can offer a zero-lag powerband with high torque at lower engine speeds and increased power at the higher end. Twincharging is therefore desirable for small-displacement motors (such as VW's 1.4TSI), especially those with a large operating RPM, since they can take advantage of an artificially broad torque band over a large speed range.
Twincharging does not refer to a twin-turbo
Twin-turbo
Twin-turbo refers to a turbocharged engine, in which two turbochargers compress the intake charge. There are two commonly used twin turbo configurations: parallel twin-turbo and sequential twin-turbo...
arrangement, but rather when two different kinds of compressors are used.
Technical description
A twincharging system combines a supercharger and turbocharger in a complementary arrangement, with the intent of one component's advantage compensating for the other component's disadvantage. There are two common types of twincharger systems: series and parallel.Series
The series arrangement, the more common arrangement of twinchargers, is set up such that one compressor's (turbo or supercharger) output feeds the inlet of another. A sequentially-organized Roots type superchargerRoots type supercharger
The Roots type supercharger or Roots blower is a positive displacement lobe pump which operates by pumping fluids with a pair of meshing lobes not unlike a set of stretched gears. Fluid is trapped in pockets surrounding the lobes and carried from the intake side to the exhaust...
is connected to a medium- to large-sized turbocharger. The supercharger provides near-instant manifold pressure (eliminating turbo lag, which would otherwise result when the turbocharger is not up to its operating speed). Once the turbocharger has reached operating speed, the supercharger can either continue contributing pressurized air to the turbocharger inlet (yielding elevated intake pressures), or it can be bypassed and mechanically decoupled from the drivetrain
Powertrain
In a motor vehicle, the term powertrain or powerplant refers to the group of components that generate power and deliver it to the road surface, water, or air. This includes the engine, transmission, drive shafts, differentials, and the final drive...
via an electromagnetic clutch
Electromagnetic clutch
Electromagnetic clutches operate electrically, but transmit torque mechanically. This is why they used to be referred to as electro-mechanical clutches. Over the years, EM became known as electromagnetic versus electro mechanical, referring more about their actuation method versus physical operation...
and bypass valve or one-way valve (increasing efficiency of the induction system).
Other series configurations exist where no bypass system is employed and both compressors are in continuous duty. As a result, compounded boost is always produced as the pressure ratios of the two compressors are multiplied, not added. In other words, if a supercharger which produced 10 psi (0.6894757293 bar) (pressure ratio = 1.7) alone blew into a turbocharger which also produced 10psi alone, the resultant manifold pressure would be 27 psi (1.9 bar) (PR=2.8) rather than 20 psi (1.4 bar) (PR=2.3) This form of series twincharging allows for the production of boost pressures that would otherwise be unachievable with other compressor arrangements.
However, the efficiencies of the turbo and supercharger are also multiplied, and since the efficiency of the supercharger is often much lower than that of large turbochargers, this can lead to extremely high manifold temperatures unless very powerful charge cooling is employed. For example, if a Roots blower with an efficiency of 60% blew into a turbocharger with an efficiency of 70%, the overall compression efficiency would be only 42% -- at 2.8 pressure ratio as shown above and 20 °C (68 °F) ambient temperature, this would mean air exiting the turbocharger would be 263 °C (505.4 °F), which is enough to melt most rubber couplers and nearly enough to melt expensive silicone couplers. A large turbocharger producing 27 psi (1.9 bar) by itself, with an adiabatic efficiency around 70%, would only produce 166 °C (330.8 °F). Additionally, the energy cost to drive a supercharger is usually several horsepower, thus if it can either be disconnected electrically (using an electromagnetic clutch such as those used on the VW 1.4TSI or Toyota's 4A-GZE) or allowed to freewheel and vent to the atmosphere, several horsepower can be gained independent of the efficiency gain by switching to one compressor.
Thus, switching the supercharger off at a certain boost or RPM threshold is most desirable, since a large, inexpensive journal bearing turbocharger can be used which will provide more than enough pressure and flow at any RPM for most twincharged motors. However, a smooth switchover can be very difficult to accomplish for non-OEM twincharging applications.
Parallel
Parallel arrangements typically always require the use of a bypass or diverter valve to allow one or both compressors to feed the engine. If no valve were employed and both compressors were merely routed directly to the intake manifold, the supercharger would blow backwards through the turbocharger compressor rather than pressurize the intake manifold, as that would be the path of least resistance. Thus a diverter valve must be employed to vent turbocharger air until it has reached the pressure in the intake manifold. Complex or expensive electronic controls are usually necessary to ensure smooth power delivery.Disadvantages
The main disadvantage of twincharging is the complexity and expense of components. Usually to provide acceptable response, smoothness of power delivery, and adequate power gain over a single-compressor system, expensive electronic and/or mechanical controls must be used. In a spark-ignition engine, a low compression ratio must also be used if the supercharger produces high boost levels, negating some of the efficiency benefit of low displacement.Commercial availability
The concept of twincharging was successfully used by LanciaLancia
Lancia Automobiles S.p.A. is an Italian automobile manufacturer founded in 1906 by Vincenzo Lancia and which became part of the Fiat Group in 1969. The company has a long history of producing distinctive cars and also has a strong rally heritage. Some modern Lancias are seen as presenting a more...
in the 1980s on the Lancia Delta S4
Lancia Delta S4
The Lancia Delta S4 is a Group B rally car that competed in the World Rally Championship in 1985 and 1986, until Group B cars were banned from competition by the FIA. The car replaced and was an evolution of the Lancia 037 Monte Carlo. The S4 took full advantage of the Group B regulations, and...
rally car. The idea was also successfully adapted to production road cars by Nissan, in their March Super Turbo
Nissan March
The Nissan Micra, known in Latin America and in most of Asia as the Nissan and in North America as the Nissan Versa , is a supermini produced by the Japanese automaker Nissan since 1982.-Micra K10:...
.
Additionally, multiple companies have produced aftermarket
Aftermarket (automotive)
The automotive aftermarket is the secondary market of the automotive industry, concerned with the manufacturing, remanufacturing, distribution, retailing, and installation of all vehicle parts, chemicals, tools, equipment and accessories for light and heavy vehicles, after the sale of the...
twincharger kits for cars like the Subaru Impreza WRX
Subaru Impreza WRX
The Subaru Impreza WRX is a turbocharged version of the Subaru Impreza, an all-wheel drive, four-door passenger vehicle. It is available as a sedan or wagon....
, Mini Cooper S, Ford Mustang
Ford Mustang
The Ford Mustang is an automobile manufactured by the Ford Motor Company. It was initially based on the second generation North American Ford Falcon, a compact car. Introduced early on April 17, 1964, as a "1964½" model, the 1965 Mustang was the automaker's most successful launch since the Model A...
, Nissan Skyline GT-R
Nissan Skyline GT-R
The Nissan Skyline GT-R is a Japanese sports car based on the Nissan Skyline range.The first GT-Rs were produced from 1969–1973. After a 16 year hiatus since the KPGC110 in 1972, the GT-R name was revived in 1989 with the Skyline R32. This car was nicknamed "Godzilla" by the Australian motoring...
, Toyota MR2
Toyota MR2
The Toyota MR2 is a two-seat, mid-engined, rear wheel drive sports car produced by Central Motors, a part of Toyota, from 1984 until July 2007 when production stopped in Japan...
, as well as the GM 3800 Engine, as in the Pontiac Bonneville
Pontiac Bonneville
The Pontiac Bonneville was an automobile built by the Pontiac division of General Motors from 1957 to 2005. It was introduced as a limited production performance convertible during the 1957 model year...
SSEI, Pontiac Grand Prix
Pontiac Grand Prix
Picking up where the Pontiac Ventura model left off, the Grand Prix first appeared in the Pontiac line for 1962. It was essentially a standard Pontiac Catalina coupe with minimal outside chrome trim and a sportier interior...
GTP, and the Chevrolet Cobalt SS
Chevrolet Cobalt SS
The Cobalt SS is a line of three sport compact versions of the Chevrolet Cobalt built on the General Motors Delta platform at Lordstown Assembly in Ohio, United States...
among others.
The Volkswagen 1.4TSI is a 1400 cc engine that utilizes both turbocharger and supercharger. It produces 170 bhp at 6000 rpm and 240 newton metre from 1500 to 4750 rpm.
Anti-lag system
Twincharging's biggest benefit over anti-lag systems now in race car applications is its reliability. Anti-lag systems work in one of two ways; by running very rich AFR and pumping air into the exhaust to ignite the extra fuel in the exhaust manifold; or by severely retarding ignition timing to cause the combustion event to continue well after the exhaust valve has opened. Both methods involve combustion in the exhaust manifold to keep the turbine spinning, and the heat from this will shorten the life of the turbine greatly.Variable geometry turbocharger
A variable-geometry turbocharger provides an improved response at widely-varied engine speeds. With variable-incidence under electronic control, it is possible to have the turbine reach a good operating speed quickly or at lower engine speed without severely diminishing its utility at higher engine speed.Nitrous oxide
Nitrous oxideNitrous oxide
Nitrous oxide, commonly known as laughing gas or sweet air, is a chemical compound with the formula . It is an oxide of nitrogen. At room temperature, it is a colorless non-flammable gas, with a slightly sweet odor and taste. It is used in surgery and dentistry for its anesthetic and analgesic...
(N2O) is mixed with incoming air, providing more oxygen to burn more fuel for high power when a turbocharger is not spinning quickly. This also causes the turbocharger to quickly accelerate, providing more oxygen for combustion, and the N2O flow is reduced accordingly. The expense of both the system itself and the consumable N2O can be significant.
Water injection
For more engine power, and to augment the benefits of forced inductionForced induction
Forced induction is the process of compressing air on the intake of an internal combustion engine . A forced induction engine uses a gas compressor to increase the pressure, temperature and density of the air...
(by means of turbocharging or supercharging), an aftermarket
Custom car
A custom car is a passenger vehicle that has been modified in either of the following two ways. First, a custom car may be altered to improve its performance, often by altering or replacing the engine and transmission. Second, a custom car may be a personal "styling" statement, making the car look...
water injection system can be added to the induction system of both gasoline and diesel internal combustion engines.
External links
- http://www.greencarcongress.com/2005/08/inside_vws_new_.html
- Bee*R's Twincharged Nissan Silvia S15