At a Glance – Turbochargers


With the ongoing movement toward global environmental protection, regulations related to the exhaust emissions and fuel consumption of automobiles are being strengthened. To cope with these requirements, turbochargers are an effective tool to improve fuel consumption and reduce carbon dioxide emissions, by reducing the engine weight and friction loss.

Since a turbocharger supplies compressed air to an engine, it can reduce the engine displacement relative to an atmospheric engine for the same power. Variable geometry turbochargers, which can control the boost pressure according to the engine operating conditions, are becoming increasingly popular, creating a demand for a centrifugal compressor with a wide and stable operational range.

A turbocharger consists of a compressor wheel and an exhaust gas turbine wheel coupled together by a solid shaft. It is used to boost the air intake pressure of an internal combustion engine. The gas turbine extracts energy from the exhaust gas and uses it to drive the compressor and overcome friction.

Of course there are some advantages and disadvantages to turbocharger systems:

•Otherwise wasted exhaust gas energy can be used to drive the compressor (see previous post)
•More specific power over a naturally-aspirated (NA) engine — it means an engine can produce more power for its size
•Reuse of excess exhaust heat (it gets channeled into the turbocharger to increase the boost of the engine) which means the engine runs more efficiently
•A turbocharger is smaller, lighter and easier to fit than a supercharger (perfect for narrow installation conditions)
•Because a small engine can be made to produce the power of a bigger engine, fuel economy is often better on a per kW basis (smaller specific fuel consumption)
•High torques for wide speed ranges

•Matching of the turbo to the engine difficult
•Slow response resulting in “turbo-lag”
•In spark ignition engines, a reduction of the compression ratio is necessary to avoid detonation
It’s all about efficiency though, and achieving maximum engine torque at low engine speeds can be a challenge with a turbocharged engine, especially in downsized engines that rely heavily on turbocharging. Do you practice turbocharger systems? What’s a key factor you use to maintain efficiency?

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