By P Sanchez
We’ve talked about the exhaust system and its common parts but I will be completely remiss if I didn’t touch on one component of the system that’s slowly becoming a usual fixture among all automobiles, whether its for high-capacity performance or small-engine fuel economy: the turbo
It’s known that a modern internal combustion engine is still largely an inefficient system, is spite of all the advancements in its workings. Estimates put the average thermal efficiency of the engine (or how much heat energy is converted to mechanical work to drive a car forward) at 12 to 30%. Much of the energy from the burning of fuel is absorbed by the cooling system which is necessary to prevent the engine from melting down. But probably the biggest portion of energy is simply ejected out the exhaust.
The most common way to scavenge the energy from exhaust flow is through the use of turbochargers. At its most basic, a turbo is nothing more than fan blades that are spun by the fluid of the exhaust. The blades are connected via a shaft to an impeller which is another type of fan blade that “sucks in” and compresses fresh air into an engine.
The principle of getting useful work out of a moving fluid might be as old as civilization itself. Windmills and waterwheels are common examples. In 1905, Swiss engineer Alfred Buchi received a German patent for the design of the first turbo-compressor for a piston-operated internal combustion engine. Only until material technology caught-up that Buchi’s design found it’s first application in marine diesel engines in 1923.
In fact, owing to the need of very high compression ratios as part of its normal 4-stroke cycle and their robust construction, diesel engines were a perfect match for turbochargers. After marine applications, turbos were applied to diesel trucks starting 1938. It was only until the 1960's that turbos have seen commercial application to gasoline engines of passenger cars, with examples like the Chevrolet Corvair Monza and the Oldsmobile Jetfire.
In the last century, the use of turbo in gasoline engines was often seen as a performance improvement and they were commonly found in race cars, high-end vehicles, or as expensive aftermarket modifications. They add a ton of horsepower but often at the expense of fuel-economy and long-term reliability. Also, simpler designs were notorious for their “lag”. This means turbochargers don’t do their desired boosting until cars get to high-rev scenarios when there’s enough exhaust flow to spool the turbo.
But better materials, smaller and more compact designs, and design advancements like twin-scrolling, turbo-compounding, variable vane geometry have not only mitigated the effects of turbo-lag and widened the turbo’s effectivity through the rev-range but these newer turbo designs have allowed suitable application to smaller engine for the purposes of improved fuel-economy.
A turbocharger is easily the most interesting feature in an exhaust system but it’s not a standard feature in all cars. It adds cost and another point of possible failure in an already complex system. But as there is increasing pressure to get the most out of every drop of fuel, we may see the day that turbos become commonplace in all cars.