In automotive turbocharger it consists of a turbine driven by exhaust gases whose shaft is a centrifugal compressor which takes air to air before or after passing through the air filter and then compressed before being fed into the cylinder pressure. This increased load pressure introduced into the cylinder gets a greater volume of mixture (fuel load) that the current volume of the cylinder allow atmospheric pressure to obtain the engine more power than a naturally aspirated engine of equal displacement. Furthermore, by reducing the cilidrada it reduces real horses in relation to tax reducing the tax burden of the vehicle in some countries.

In gasoline engines, usually indirect injection, fuel is injected into the passage between the supercharger and the combustion chamber (intake manifold). In a direct injection diesel engine, fuel is introduced directly into the combustion chamber at the end of the compression phase when the air charge has reached its highest temperature.

Nowadays it is usually interposed between the turbocharger and the cylinder heat exchanger or intercooler as to compress it heats fluid and in doing so, loses density causing decreased engine performance for existing fewer oxygen atoms per unit volume in the fuel mix. The intercooler reduces the temperature of the load causing an increase in density, which increases mass of O2 in relation to the volume of the mixture, increasing the combustion efficiency.

As the energy used for compressing the intake air comes from exhaust gases, this system does not reduce engine power unlike mechanical compressor systems (systems where the compressor is driven by a pulley connected to the crankshaft). Engines equipped with turbochargers, however, suffer from a delay in the provision of higher power than atmospheric engines or mechanical compressor, because the efficiency of the turbocharger depends on the pressure achieved by this and achieve the proper pressure, the turbocharger must be turning adequate arrangements. This delay inertia influence group (its diameter and weight) and the manifold volume between the turbine and the output of the exhaust gas cylinder.

There are different designs to reduce the response time of the turbocharger, including:

An alternative design to a biturbo (use of two turbochargers groups) applied by the manufacturer on the Swedish SAAB Saab Saab 9-5 V6. It is called asymmetric turbo is one small turbo put on a bench (the lead in the V6 engine placed transversely) leaving the other free. The idea is not to get a great power, but the answer is, above all, fast.

Another way to reduce the delay is the sequential twin turbo system used by Mazda Wankel engine in the RX-7. By using two turbochargers in series, when there is little volume exhaust all this volume is sent to a turbocharger, and when volume increases, is divided between the two turbochargers for increased power and reduced response time.

Currently it is changing the philosophy of application of turbos, it prevailed before the power at high RPM and now increasingly, the car responds well throughout the engine speed of use. For this smaller turbos and lower blowing pressures, up to 0.25 bar (approx. 3625 psi) Saab 9-5 in turbo V6 instead they are used when one wants power systems reaching values ​​of 0.9 are designed -1.5 bar (13.05 – 21.75 psi).

These maximum pressures are limited by a so-called waste-gate valve used to prevent excessive pressure that can damage the engine. On some models this excessive pressure is maintained only for a short time, about 1 minute when the accelerator is pressed. These systems are called overdrive or overboost.

In turbocharged diesel engines is the most widespread because a diesel engine that works by autoignition, i.e., the mixture ignites spontaneously with increasing temperature thereof. This temperature is achieved by increasing the pressure of the air charge in the cylinder during the compression phase and reached the highest temperature of the charge air, fuel oil (diesel oil) is injected by combustion spontaneously, obviating the ignition system (distributor spark coils, spark plugs, etc.) by increasing the volume of the air charge during the intake stroke by using a turbocharger, is achieved significantly increase the Diesel engine performance and capacity response.

In gasoline engines, however, reduce the compression ratio to avoid knock. This causes a decrease in performance (for the same power consumption is obtained less), so that consumption is higher than in a naturally aspirated engine, even when not a lot of power demand. To mitigate this problem, the Saab brand has devised a system of variable compression, whereby 225 hp are available in a 1.6-liter normal consumption of a 1.6.

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