SOMETHING for nothing; that was the premise of a turbocharger. All of us have seen that prominent badge on the bootlid of a car and probably wondered what it was.
The one thing we knew for sure was that a turbocharged car would be awful fast. But what is a turbocharger and how does it work?
Turbochargers, or turbos for short, have been around a long time. Alfred J. Buchi, an automotive engineer employed by the Gebr¸der Sulzer Engine Company of Winterthur, Switzerland, designed an exhaust-driven turbine shaft to power a compressor that forced more air into an engine’s cylinders.
He originally developed the turbocharger in the years before World War 1 and patented it in Germany in 1905. Theoretically, waste exhaust gasses would not just be wasted energy but instead used to increase an engine’s output.
Internal combustion engines use fuel to produce power. Once burnt, the resulting spent gasses exit the exhaust, never to be used as fuel again or to power anything else.
Normally, the fuel burnt in a normally aspirated engine (that’s what we turboheads call normal car engines) produces a certain amount of power and, with careful tuning and modification, produces its optimum output.
The power is directly related to how fast and how much fuel it is able to burn so engineers focus on how well the engine breathes and how fast the engine will spin.
Another way to increase power is to add more capacity or add more cylinders. Obviously, this adds weight and/or complexity. How about we use the engine we designed earlier and just add this thing called a turbo?
In a nutshell, a turbo is a turbine connected by a shaft to a compressor. The turbo uses the spent exhaust gasses to power the turbine, much like a hydroelectric station uses water to spin its own turbine.
The compressor on the opposite end of the shaft hence spins at the same rate as the turbine. Both turbine and compressor wheels are basically designed like a fan, only one is designed to be pushed by exhaust gasses, the other designed to push air.
Both are fed by specially designed housings, shaped like a snail shell but obviously opposite or mirror images to each other.
The housings’ design helps the air/exhaust move or expand in a certain manner. The aluminium housing is the compressor and the cast iron housing (which resists heat) is the turbine.
Turbochargers will increase the pressure and density of air entering the engine. This is measured either in PSI, or Bar. However, as the pressure increases and as the engine spins faster, it will result in a vicious cycle of increasing pressure spinning the engine too fast until it self-destructs.
To control this, a wastegate is fitted to the turbine side which will deflect the incoming exhaust gasses out straight to the exhaust pipe. This wastegate is controlled by the compressor side. An actuator arm connected to the compressor will open the wastegate at a certain amount of pressure defined by the engineer.
However, not all is nice and dandy. As we compress intake air, we also will raise its temperature. Hot air does not burn very nicely as it is less dense (less oxygen molecules) and it is then necessary to cool it down before entering the engine.
This is the function of the intercooler. Sometimes, the intercooler is cooled further by water (or even ice!) in extreme applications.
Even more extreme is the practice of injecting water into the air stream entering the engine itself.
So now our old engine is producing more power (and thus more heat). As we increase the pressure (called boost pressure) the engine now starts to eats components at a faster rate than before.
Pistons melt, cylinders crack, crankcases burst open and even bolts get stretched. A turbocharged engine requires less compression ratio, stronger pressure cast (or forged) pistons, heavy-duty bolts, strengthened crankcases, higher-duty oil pumps and a myriad of other detail improvements over a normally aspirated engine.
So the same engine will need a full redesign to accommodate the turbocharger. Once we get the engine reliable, we strap on a larger, more powerful turbocharger and the cycle begins again.
In the end, it will eventually hit a limit. The cylinders are only as big as you can make them and there’s only so much fuel they can burn.
There is only so much air you can force into them through an inlet of a certain size and obviously only so much exhaust gas you can expel, which eventually limits the energy you can use to drive your turbocharger.
The basic advantage of using a turbocharger is that you get more power for the same size of engine. However, more energy produced means it needs more energy producing fuel.
In theory, that means an engine with a turbocharger is not necessarily more fuel efficient than one without. But an engine fitted with a turbocharger is usually of much smaller capacity and is able to be lighter than an engine producing the same power without a turbocharger.
And since they burn fuel with more oxygen, they tend to burn it more thoroughly and cleanly, producing a more efficient, cleaner car.
Turbos are now commonplace and need no more maintenance than a normally aspirated engine. The only important thing to remember if you own a turbocharged vehicle is; always use the correct oil (designed for turbo cars) and to change it regularly.
Turbos spin at insane speeds (over 150,000rpm in some cases) and need good lubrication.
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