The Physics of Turbochargers and How They Can Be Used to Increase a Car’s MPG

(Image Above - http://www.hybridcars.com/)
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With increased gas prices and a growing interest in environmental issues, many people worldwide have been looking to purchase cars with high miles per gallon (mpg) ratings. Making cars that have good gas mileage can be accomplished in various ways; including weight reduction using better aerodynamics and smaller engine, decreasing engine consumption, and using alternative power sources such as electricity. A drawback to making cars with good gas mileage is the possibility of sacrificed power. Some car buyers would like to have cars with higher mpg ratings, but do not want to sacrifice the performance of their vehicle in order to obtain it. As a result, many car companies have resorted to an engine addition known as a turbocharger to make powerful vehicles while sustaining a respectable gas mileage (http://www.hybridcars.com).
Turbochargers are a type of forced induction system that can be added to a car’s engine to increase the overall power, while also allowing the engine to better withstand extreme operating conditions. The turbocharger compresses the air entering the engine it is attached to. This compression allows the engine to squeeze more air into each cylinder, meaning more fuel can be added. With more fuel in the cylinders, a larger explosion can occur, resulting in more power output. The increased power improves the power-to-weight ratio of the engine (Nice 2000).
(Right Image - Nice 2000)

In order for the turbocharger to achieve its “boost,” it uses the flow through the car’s exhaust to spin a turbine, which in turn, spins an air pump. The turbine in the turbocharger has the capability to spin at speeds up to 150,000 rotations per minute, which is about 30 times faster than the engines of most cars. The typical boost provided by turbochargers is around six to eight pounds per square inch (psi). The atmospheric pressure at sea level is 14.7 psi, meaning a turbocharger is moving about 50 percent more air into the engine. The turbocharger, however, does not result in 50 percent more power. Instead, the power output is typically increased by 30-40 percent due to certain inefficiencies resulting from the a turbine in the exhaust system (Nice 2000).

(Image Left - Nice 2000)

Using a turbocharger is usually a more feasible solution for getting more power out of an engine than adding more cylinders or making current cylinders larger. A turbocharger is simpler, lighter, cheaper ($250-$500 per vehicle), and consumes less fuel than a larger engine. Turbochargers can also be easily integrated into existing car powertrains, making it a viable product for use by major car companies. Theoretically, a turbocharged six-cylinder engine can have the same or more power than a conventional eight-cylinder engine. For this reason, turbochargers have been referred to as the new hybrid. General Motors is planning to downsize some of their engines in current car models in order to achieve better gas mileage. Turbochargers are being used to make up for the use of smaller engines. In fact, with the use of turbochargers, G.M. has been able to place a 1.4 liter engine in certain car models, which is the smallest engine used by the company in the past fifteen years. Ford has plans to further use their “EcoBoost” technology, which utilizes both direct injection and turbocharging to yield as much as a 20 percent increase in fuel economy. Once
only used to boost the power of cars built for racing, turbochargers have evolved to be used as a way to save fuel without sacrificing performance (http://www.hybridcars.com/).
(Image Above/Right - Nice 2000)


Cited:

Nice, Karim. "How Turbochargers Work." 04 December 2000. .

“Turbocharging, the New Hybrid.” 04 February 2008. .