What is a turbocharger?
The Turbo charger was firstly developed for the commercial sector in 1924, it uses the engine’s exhaust fuel to power a turbine, which drives a compressor, and pushes more air into the engine. This allows the engine to produce more power without any increase in size. Turbochargers have provided such significant improvements in engine efficiency that they are now fitted to almost all new diesel and petrol engines.
It is also known as the device driven by exhaust gases that increases engine power by pumping air into the combustion chambers. Combustion is limited not by the amount of fuel that can be injected but by the amount of air an engine can gulp in to mix with that fuel.
All turbochargers operate at a very high speed. This can range from 40,000 to over 300,000 rpm.
THE PURPOSE OF A TURBO CHARGER
Twin Passage Turbine
In twin-scroll designs, the exhaust manifold physically separates the channels for cylinders that can interfere with each other, so that the pulsating exhaust gasses flow through separate spirals (scrolls). With common firing order 1-3-4-2, two scrolls of unequal length pair cylinders 1-4 and 3-2.
Also called Twin Flow, Twin Port or Dual Port Turbochargers, this refers to the turbine (exhaust) hous design with 2 exhaust entry ports. To better utilise these impulses, one design has an internal division in the turbine housing and the exhaust manifold which directs these exhaust gases to the turbine wheel. There is a separate passage for each half of the engine cylinder exhaust.
On a six-cylinder engine, there is a separate passage for the front three cylinders and another passage for the rear three cylinders.
By using a fully divided exhaust system combined with a dual scroll turbine housing, the result is a highly effective nozzle velocity. This produces higher turbine speeds and manifold pressures than can be obtained with an undivided exhaust system.
This type of turbine housing design matched to a split pulse exhaust manifold design lifts low engine speed performance but making the turbine side of the turbo up to approx 15% more efficient.
The benefit of this is that you can still use a relatively unrestricted large A/R housing but still maintain good boost response. This concept has been used in Diesel applications for a several decades but is only beginning to gain popularity in the performance tuning scene.
Why use Turbochargers?
There are five basic reasons for using an engine turbocharger:
1. To increase horsepower output of a given displacement engine: Where the engine compartment of a machine is of a given size, a turbocharged engine can be used to provide increased horsepower without having to enlarge the engine compartment for a larger displacement engine.
2. To reduce weight: Turbocharged engines have more horsepower per Kilogram than non-turbocharged engines.
3. To keep down costs: Initial cost of turbocharged engines, on a dollar per horsepower basis, is less than for a naturally aspirated (N.A.) engine, and the differential increases with the rate of turbocharging. It all adds up to more horsepower per dollar.
4. To maintain power at higher altitudes: The altitude compensator also falls in this category, giving vital machine productivity at high altitudes.
5. To reduce smoke: Turbocharging can be an effective way to reduce exhaust density by providing excess air. However, using a turbocharger does not ensure this, as many other components also affect exhaust density and these must be properly designed and matched to provide an acceptable smoke level.
There are four basic ways of using multiple turbochargers on an engine:
1. Twin Turbo. This is where you have 2 turbos being fed exhaust gas from half of the engine each. This is popular in a “V” type engine where one banks exhaust gas feeds each turbo. This is still single stage turbocharging, but using more than one turbo to achieve the desired boost pressure. Common on petrol/gasoline engines.
2. 2 Stage compounding Turbochargers. This is where you have a small High pressure (HP) turbo mounted close to the engines exhaust ports and a larger Low Pressure (LP) turbo being fed from the waste gasses the are coming from the HP turbo without any valving. Sometimes this system uses a wastegate to control the peak pressure. Usually found on hip powered diesel engines where high boost pressures are required. This system offers good throttle response while still achieving high engine performance and very high boost levels by way of compounding the boost pressure.
3. Staged Turbocharging. This is where you have 2 turbos, one larger than the other in a staged setup using valving to bring the 2nd (usually larger) turbo into play at a desired engine speed or load. This system offers good throttle response as well as high volumes of air flow. Typically thr boost pressure is not compounded in this setup.
4. Regulated 2 Stage Turbocharging. This system is complex with valving used to control both the airflow and the exhaust gasses. it provides a seamless transition into high boost with amazing response and can offer very high performance. This system can be used with 2, 3 or more turbos for great effect. Also commonly used with VNT style variable geometry turbochargers.