Turbo Facts

Here you can find out more about our fascinating turbocharger products. The history of turbocharging from its beginning up to today. Learn more about the basic technology behind the turbocharger as well as the advantages that turbocharging offers in terms of performance, fuel consumption and pollutant emissions. Experience its evolution and the steps necessary to develop turbocharging: from the initial idea up to its readiness for mass production. Furthermore, you will find information on care and maintenance as well as diagnostic aids if a problem should actually arise.

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History

The history of turbocharging is almost as old as that of the internal combustion engine. As early as 1885 and 1896, Gottlieb Daimler and Rudolf Diesel investigated increasing the power output and reducing the fuel consumption of their engines by precompressing the combustion air. In 1925, the Swiss engineer Alfred Büchi was the first to be successful with exhaust gas turbocharging, and achieved a power increase of more than 40 %. This was the beginning of the gradual introduction of turbocharging into the automotive industry. 

The first turbocharger applications were limited to very large engines, e.g. marine engines. In the automotive engine industry, turbocharging started with truck engines. In 1938, the first turbocharged engine for trucks was built by the "Swiss Machine Works Saurer". 

The Chevrolet Corvair Monza and the Oldsmobile Jetfire were the first turbo-powered passenger cars, and made their debut on the US market in 1962/63. Despite maximum technical outlay, however, their poor reliability caused them to disappear quickly from the market. 

After the first oil crisis in 1973, turbocharging became more acceptable in commercial diesel applications. Until then, the high investment costs of turbocharging were offset only by fuel cost savings, which were minimal. Increasingly stringent emission regulations in the late 80's resulted in an increase in the number of turbocharged truck engines, so that today, virtually every truck engine is turbocharged. 

In the 70's, with the turbocharger's entry into motor sports, especially into Formula I racing, the turbocharged passenger car engine became very popular. The word "turbo" became quite fashionable. At that time, almost every automobile manufacturer offered at least one top model equipped with a turbocharged petrol engine. However, this phenomenon disappeared after a few years because although the turbocharged petrol engine was more powerful, it was not economical. Furthermore, the "turbo-lag", the delayed response of the turbochargers, was at that time still relatively large and not accepted by most customers. 

The real breakthrough in passenger car turbocharging was achieved in 1978 with the introduction of the first turbocharged diesel engine passenger car in the Mercedes-Benz 300 SD, followed by the VW Golf Turbodiesel in 1981. By means of the turbocharger, the diesel engine passenger car's efficiency could be increased, with almost petrol engine "driveability", and the emissions significantly reduced. 

Today, the turbocharging of petrol engines is no longer primarily seen from the performance perspective, but is rather viewed as a means of reducing fuel consumption and, consequently, environmental pollution on account of lower carbon dioxide (CO2) emissions. Currently, the primary reason for turbocharging is the use of the exhaust gas energy to reduce fuel consumption and emissions. 

Principles of Turbocharging

To better understand the technique of turbocharging, it is useful to be familiar with the internal combustion engine's principles of operation. Today, most passenger car and commercial diesel engines are four-stroke piston engines controlled by intake and exhaust valves. One operating cycle consists of four strokes during two complete revolutions of the crankshaft.

Schematic of a fourstroke piston engine
Schematic of a fourstroke piston engine
  • Suction (charge exchange stroke)
    When the piston moves down, air (diesel engine or direct injection petrol engine) or a fuel/air mixture (petrol engine) is drawn through the intake valve.
  • Compression (power stroke)
    The cylinder volume is compressed.
  • Expansion (power stroke)
    In the petrol engine, the fuel/air mixture is ignited by a spark plug, whereas in the diesel engine fuel is injected under high pressure and the mixture ignites spontaneously.
  • Exhaust (charge exchange stroke)
    The exhaust gas is expelled when the piston moves up.
 
Principles of Turbocharging: Efficiency
These simple operating principles provide various possibilities of increasing the engine's power output

Swept volume enlargement

Enlargement of the swept volume allows for an increase in power output, as more air is available in a larger combustion chamber and thus more fuel can be burnt. This enlargement can be achieved by increasing either the number of cylinders or the volume of each individual cylinder. In general, this results in larger and heavier engines. As far as fuel consumption and emissions are concerned, no significant advantages can be expected.

Increase in engine rpm

Another possibility for increasing the engine's power output is to increase its speed. This is done by increasing the number of firing strokes per time unit. Because of mechanical stability limits, however, this kind of output improvement is limited. Furthermore, the increasing speed makes the frictional and pumping losses increase exponentially and the engine efficiency drops.

Turbocharging

In the above-described procedures, the engine operates as a naturally aspirated engine. The combustion air is drawn directly into the cylinder during the intake stroke. In turbocharged engines, the combustion air is already pre-compressed before being supplied to the engine. The engine aspirates the same volume of air, but due to the higher pressure, more air mass is supplied into the combustion chamber. Consequently, more fuel can be burnt, so that the engine's power output increases related to the same speed and swept volume.

Basically, one must distinguish between mechanically supercharged and exhaust gas turbocharged engines.
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Schematic of a mechanically supercharged four-cylinder engine

Mechanical supercharging

With mechanical supercharging, the combustion air is compressed by a compressor driven directly by the engine. However, the power output increase is partly lost due to the parasitic losses from driving the compressor. The power to drive a mechanical turbocharger is up to 15 % of the engine output. Therefore, fuel consumption is higher when compared with a naturally aspirated engine with the same power output.
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Schematic of an exhaust gas turbocharged four-cylinder

Exhaust Gas Turbocharging

In exhaust gas turbocharging, some of the exhaust gas energy, which would normally be wasted, is used to drive a turbine. Mounted on the same shaft as the turbine is a compressor which draws in the combustion air, compresses it, and then supplies it to the engine. There is no mechanical coupling to the engine.

Advantages of Exhaust Gas Turbocharging

Compared with a naturally aspirated engine of identical power output, the fuel consumption of a turbocharger engine is lower, as some of the normally wasted exhaust energy contributes to the engine's efficiency. Due to the lower volumetric displacement of the turbo engine, frictional and thermal losses are less.

The power-to-weight ratio, i.e. kilowatt (power output)/kilograms (engine weight), of the exhaust gas turbocharged engine is much better than that of the naturally aspirated engine.

The turbocharger engine's installation space requirement is smaller than that of a naturally aspirated engine with the same power output.

A turbocharged engine's torque characteristic can be improved. Due to the so-called "maxidyne characteristic" (a very high torque increase at low engine speeds), close to full power output is maintained well below rated engine speed. Therefore, climbing a hill requires fewer gear changes and speed loss is lower.

The high-altitude performance of a turbocharged engine is significantly better. Because of the lower air pressure at high altitudes, the power loss of a naturally aspirated engine is considerable. In contrast, the performance of the turbine improves at altitude as a result of the greater pressure difference between the virtually constant pressure upstream of the turbine and the lower ambient pressure at outlet. The lower air density at the compressor inlet is largely equalized. Hence, the engine has barely any power loss.

Because of reduced overall size, the sound-radiating outer surface of a turbocharger engine is smaller, it is therefore less noisy than a naturally aspirated engine with identical output. The turbocharger itself acts as an additional silencer.

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