Twincharger
Twincharger refers to a compound forced induction system used on some piston-type internal combustion engines. It is a combination of an exhaust-driven turbocharger and a mechanically-driven supercharger, each mitigating the weaknesses of the other. A mechanically-driven supercharger offers exceptional response and low-rpm performance as it does not rely on pressurization of the exhaust manifold. A turbocharger sized to move a large volume of air tends to respond slowly to throttle input while a smaller, faster-responding turbo may fail to deliver sufficient volume through an engine's upper RPM range. The unacceptable lag time endemic to a large turbocharger is effectively neutralized when combined with a supercharger which tends to generate substantial boost pressure much faster in response to throttle input. The end result being a zero-lag powerband with high torque at lower engine speeds and increased power at the upper end. Twincharging is therefore desirable for small-displacement motors, 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 where 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 output feeds the inlet of another. A sequentially organized supercharger is connected to a medium- to large-sized turbocharger. The supercharger provides near-instant manifold pressure. Once the turbocharger has reached operating speed, the supercharger can either continue compounding the pressurized air to the turbocharger inlet, or it can be bypassed and/or mechanically decoupled from the drivetrain via an electromagnetic clutch and bypass valve.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 turbocharger which produced alone blew into a supercharger which also produced 10 psi alone, the resultant manifold pressure would be rather than . This form of series twincharging allows for the production of boost pressures that would otherwise be unachievable with other compressor arrangements and would be inefficient.
However, turbo and supercharger efficiencies do not multiply. For example, if a turbocharger with an efficiency of 70% blew on a Roots blower with an efficiency of 60%, the total compression efficiency would be somewhere in between. To calculate this efficiency, it is necessary to do the calculations of the 2 stages, first calculate the conditions of pressure and temperature at the exit of the first stage and starting from these to do the calculations for the second stage. Following the previous example, for a first stage of the turbocharger the temperature would reach the after the first stage, to then enter the roots and leave at a temperature of. This is a total efficiency of 62%. A large turbocharger that produces by itself, with an efficiency adiabatic of around 70%, would produce air only. In addition, the cost of energy to drive a supercharger is higher than that of a turbocharger; if it is ignored, the load of execution compression is eliminated, leaving only light parasitic losses of rotating the working parts of the supercharger. The supercharger can be disconnected even more electrically which eliminates this small parasitic loss.
With series twincharging, the turbocharger can be of a less expensive and more durable journal bearing variety, and the sacrifice in boost response is more than made up for by the instant-on nature of displacement superchargers. While the weight and cost of the supercharger assembly are always a factor, the inefficiency and power consumption of the supercharger is almost totally eliminated as the turbocharger reaches operating rpm and the supercharger is effectively disconnected by the bypass valve.
Parallel
Parallel arrangements typically require the use of a bypass or diverted 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.Efficiency
Efficiency plays a huge role in ruling whether a car is practical for everyday tasks or if it is more suitable for track days. To find an equilibrium between the two using a twincharged system a few upgrades will be needed. Upgrades usually include the installation of a larger Intercooler, a high volume water pump, new sensors to monitor air pressure and heat, and a programmable engine management system.The most tedious in terms of physical labor is the installation of the intercooler. Intercoolers should be chosen by application and elevation. One example of an application for intercoolers is off-road vehicles. If a forced induction system is being used in an off-road vehicle, it is going to run hotter simply because of weight. The more weight being pulled along, the more work the engine must produce. If the intercooler is an air to water style system, it is imperative to have a clean source of air going into the core fins. Since this upgrade adds more coolant into the system it is important to be able to move the coolant throughout the entire system.
To obtain an optimal efficiency within the cooling system a high-volume water pump must be added. High performance water pumps have the ability to force larger quantities of water through the engine, superchargers, and turbochargers. The average stock water pumps usually work at a capacity of 35-50 gallons per minute depending on brand. If an aftermarket Pump is purchased and installed it can up that figure to 60-85 gallons per minute. This improves the cooling capabilities of the water pump for the forced induction system by 58%. To ensure that the cooling efficiency stays at its optimal level a series of checks and balances must be established.
Just like the human body an equilibrium must be maintained within an Internal combustion engine introduced to a forced induction system. Much like the bodies nervous system modern combustion engines have electrical sensors to keep all functions running within a certain tolerance zone. To keep track of all of the sensors in the system a programmable engine management system is implemented. This allows tolerances to be altered on the fly. This ECU is also the foundation for adaptive controls for the forced induction system. If one of the sensors reads that there is too much air in the system, the programmer can make it so that the system automatically compensates for the deficiency.
Disadvantages
The main disadvantage of adding any forced induction system 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 first used by Lancia in 1985 on the Lancia Delta S4 Group B rally car and its street legal counterpart, the Delta S4 Stradale. 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, and Toyota MR2.
The Volkswagen 1.4 TSI is a 1400 cc engine – utilised by numerous automobiles of the VW Group – that sees use of both a turbocharger and a supercharger, and is available with eight power ratings:
| Power | Torque | Vehicles |
| at 5,600 rpm | at 1,500–4,000 rpm | VW Golf V, VW Jetta V, and VW Touran |
| at 5,800 rpm | at 1,250–4,500 rpm | SEAT Ibiza IV |
| at 5,800 rpm | at 1,500–4,000 rpm | VW Passat VI, VW Passat VII, VW Touran |
| at 5,800 rpm | at 1,750–4,000 rpm | VW Sharan II, VW Tiguan, SEAT Alhambra |
| at 5,800 rpm | at 1,500–4,500 rpm | VW Eos, VW Golf VI, VW Jetta VI, VW Scirocco III |
| at 6,000 rpm | at 1,500–4,500 rpm | VW Golf V, VW Jetta V, VW Touran |
| at 6,200 rpm | at 2,000–4,500 rpm | VW Polo V, SEAT Ibiza Cupra, Škoda Fabia II |
| at 6,200 rpm | at 2,000–4,500 rpm | Audi A1 |
Volvo produces a twincharged 1969 cc inline-four engine that is utilised in their T6, T8, and Polestar models. The T8 adds on the T6 with a rear electric motor.
| Power | Torque | Vehicles |
| at 5,700 rpm | at 2,200–5,400 rpm | T6 |
| at 6,000 rpm | at 3,100–5,100 rpm | Polestar |
| T8 |
The Danish supercar Zenvo ST1 made use of both turbocharger and supercharger in its 6.8-litre V8 engine.
| Power | Torque | Vehicles |
| at 6,900 rpm | at 4,500 rpm | ST1 |