TURBOCHARGER
Centrifugal Pumps on an engine are similar to that of a pool pump. Centrifugal air pumps driven by an engine were very popular in the early days of American oval track racing. A Swiss engineer, named Buchi, back in 1909 created the first Turbocharger.
It took a long time for turbochargers to become established, but in the last 40 years they have become universal on most diesel powered engines. Their characteristics are particularly suited to diesel engines. Much has been written about turbo lag, a slight hesitation when extra power is demanded. But in the later designs it has almost been eliminated.
Turbochargers are more complicated than Superchargers, but its purpose is the same as a supercharger which is to increase the density of air entering the combustion chamber. However, a turbo or ‘centrifugal supercharger’ does not rely on engine mechanics to spin its turbines. Instead turbos use exhaust gasses to do this job. For that reason a Turbo has two impellers either end of a common shaft. Exhaust gas which is already at high pressure, is fed into the turbo and spins the turbine at staggering speeds of around an average, 175,000 RPM. On the other end of the drive shaft, the air intake turbine also spins at the same speed and thereby increases the density of air which is forced into the engines combustion chamber. The turbine shaft is supported on a wide supporting bearing, usually in the form of a free-floating bush.
As with Superchargers, a by-product of a turbo is immense heat. This heat needs to be managed effectively in order to increase the efficiency of a Turbo. A Turbocharger requires an intercooler to cool air flow as well as the lubrication of bearings to increase efficiency. On a Turbo, which is more efficient than a Roots Blower, temperature rises of 75 degrees Celcius are common at a boost of 100 kPa or one BAR, which implies manifold temperatures of 110 degrees Celcius.
Although, the Original Equipment Manufacturers (OEM), Turbocharged and Supercharged installation engines are subjected to stringent tests, such as 1000 hours on a dynamometer test bed, at almost full throttle, engines fitted with these high performance additions add levels of stress to the powerplant.
In theory, the life of the engines bottom end should not be affected because the addition of a low-pressure turbo (up to 100kPa boost or one BAR), actually lowers the average bearing loads at higher engine speeds.
When driving a Turbocharged vehicle, avoid accelerating from low engine speeds at large throttle opening in a high gear. These greater torque values load the engine and its drivetrain considerably, especially if it’s a diesel turbo. Any naturally aspirated engine will outlast a modified high performance engine, but compromises performance and fuel economy.
Decreasing temperature is a well known performance tuning trick. In racing terminology and in simple-terms, it means qualifying a racing car on a cold day, and we all know from experience that this works because an engine runs better when ambient temperatures are low.
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