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Written by: Susan Miles
Written on: October 3rd, 2005
Tags: mechanical engineering, energy & sustainability, transportation
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About the Author
Susan Miles graduated with a degree in Aerospace Engineering from USC in 2007. She is currently working at Lockheed Martin on the F-22 Raptor.
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Volume IX Issue III > Turbochargers
Turbocharging, a technology originally developed for use in aircraft, is a current trend among automobile enthusiasts. Applying a turbocharger to an internal combustion engine increases the power output of that engine, allowing for greater acceleration and higher maximum speeds. Turbochargers increase an automobile's power-to-weight ratio by harnessing the exhaust from the engine. They can also make a car more environmentally friendly, since they output more power while consuming the same amount of fuel. Automobile manufacturers are researching the fuel saving capacity of turbochargers in light of modern oil shortages.
In the climax of the movie The Fast and the Furious: Tokyo Drift, the main character, Sean Boswell, is racing down the side of a Japanese mountain in a '67 Ford Mustang. This, however, is not an ordinary Mustang. With the help of his father and friends, Sean has installed a salvaged Nissan VQ35DE V6 Twin Turbo engine into his car. Turbo is short for turbocharger, and this engine's two turbochargers boost the power output to a full 460 horsepower, giving Sean the speed and fast acceleration to defeat the competition [1]. Turbochargers are no longer just for cars in the movies. Several commercially available vehicles come with turbocharged engines direct from the factory, such as the Audi A6 2.7T, and most other cars can have aftermarket turbochargers or other boosting devices installed. Aside from improving the car's raw power, turbochargers can also improve gas mileage and possibly provide some relief to modern oil shortages.

A Brief History of the Turbocharger

The first turbocharger was patented in 1905 by Alfred Bucchi of Switzerland, who then built the first prototype in 1915. In the United States, the General Electric Company built a turbocharger and tested it on a diesel-powered biplane in 1920. This turbocharged plane broke records and soared to heights of 36,000 ft, the altitude at which modern commercial aircraft fly [2]. During World War II, General Electric became involved with the Garret Corporation in turbocharger production and, in 1954, Garret formed a group to focus specifically on turbocharger design and production. They founded the AiResearch Industrial Division, which later became Garret Automotive [3]. In 1961, Garret produced the first turbocharger for use in passenger vehicles. The device was coupled with the Oldsmobile Aluminum 215 "Rockette" engine and deployed on Jetfire sports cars from 1962-1963 [4]. Despite this early introduction, turbocharging did not become popular in general consumer automobiles until the late 1980s.

Internal Combustion Engines

Modern vehicles are run by internal combustion engines (ICE). These ICEs are powered by a number of pistons and cylinders: a car can be a "four cylinder" (like a Honda Civic), "six cylinder" (like a Lexus IS 250), or an "eight cylinder" (like a Ford Mustang GT). These cylinders work in combination with pistons to create power in a four-step process: intake, compression, combustion, and exhaust. Intake occurs when the piston moves down in the cylinder, creating empty space, or a vacuum, into which a fuel and air mixture will flow from the carburetor. Once the cylinder is full of the mixture, the rotating shaft pushes the piston up, compressing the fuel and air so they become extremely dense. At the top of its rotation, the piston hits a spark plug, creating a spark and igniting, or combusting, the fuel. The explosion caused by ignition forces the piston down again, powering the shaft rotation and allowing the exhaust to exit the cylinder. The shaft rotation turns the wheels of the automobile [5].

Horsepower

Horsepower is a unit of measure that is used to characterize the power of an engine. The term is derived from the literal amount of force that one horse could output over time, that is, how far (1 ft) a horse could carry a specific weight (33000 lbs) in one minute [6]. So, when a car has a 300 horsepower (hp) engine, it can pull the same weight 300 times farther than a horse could in one minute. Increasing the horsepower directly improves the acceleration, towing capacity, and maximum speed of a vehicle.

Adding a Turbocharger

A turbocharger is a compressor that forces a greater quantity of the fuel and air mixture into the engine's intake and pistons than a naturally aspirated engine does. In a turbocharger, a compressor wheel is spun by an attached turbine wheel, which is spinning in the already flowing exhaust from the engine. The spinning wheel has fan blades to compress the air that forces its way into the cylinder intake. Since there is a greater mass of airborne gasoline in the cylinder, a more powerful combustion forces the piston down at a higher speed, putting more torque on the engine shaft [7]. This power can decrease the engine's specific fuel consumption (SFC), its fuel-burned-to-power​-output ratio, by as much as 14% [8].

Turbocharger Selection

Turbochargers vary in sizes and specifications. A general rule for selecting a turbocharger to use in a street vehicle is to choose the smallest possible turbocharger that still provides the desired performance. This suggestion can be attributed to a phenomenon known as "turbo lag." Because the turbocharger is spun by exhaust fumes, there is a short time lapse between the moment the accelerator is depressed and the moment the turbocharger responds. This lag is caused by the presence of exhaust fumes in the system. For a turbocharger to spin and do its job, exhaust fumes must first be present, then fill the turbine housing, and finally provide enough pressure to move the turbine. This problem is minimized with a small turbocharger because it takes less exhaust pressure to spin a smaller turbine. However, at faster speeds, a larger turbocharger is capable of providing a greater power boost to the engine [9].
NASA
Figure 1: Cutaway photograph of NASA's oil-free turbocharger.

Turbocharging vs. Supercharging

Another way of getting more horsepower out of an engine is by supercharging. A supercharger works the same way as a turbocharger, compressing the air before it enters the engine. However, a supercharger's compressor is spun by mechanical means, such as a belt, chain, or gear, by the engine shaft rotation. This method of compressing the air is just as effective as using exhaust fumes, like a turbocharger, but it is also less efficient, using more gasoline than a turbocharger. Superchargers need to steal some of the power from the engine shaft in order to run the mechanical portion, whereas a turbocharger acts passively, being propelled only by the already existing, and otherwise wasted, exhaust [8].

Alternative Turbocharger Applications

Since turbochargers give engines lower specific fuel consumption (the engines output more overall power for less fuel burned), manufacturers are looking at benefits that are not simply related to improving a car's speed. A turbocharger on a smaller engine can output the same power as a larger engine for less fuel. Furthermore, because the car will weigh less with a smaller engine, the smaller turbocharged engine could have better performance than the original large engine without a turbocharger.
As a result, environmentalists are beginning to see that turbocharging can be used effectively not just by speed hungry motorists, but also by the environmentally conscious. Less fuel burned means fewer greenhouse gas emissions [10]. Honda's new hybrid ICE/electric Accord employs a turbocharger in this vein. The turbo-hybrid version goes from 0-60 miles per hour in two fewer seconds than its fully ICE counterpart, while using the same amount of fuel [11].

Legality of Turbocharging

Turbocharging is illegal in various forms and should not be done without consulting local legislation. Many states consider turbocharger installation to be tampering with the lawfully required emissions system. Owners of vehicles equipped with an aftermarket or non-manufacturer installed turbocharger may be fined or have their cars impounded.

Conclusion

Turbochargers are an effective means of lowering an engine's specific fuel consumption and increasing its power output to fuel-burned ratio. Historically, they have been used only to improve a car's performance specifications, but newer applications are being researched in environmental and cost-saving areas. Because of the current worldwide oil crisis, automobile manufacturers are beginning to research the fuel saving applications of the turbocharger. Who knew that what was once considered a toy for speed mongers might provide temporary relief to the energy crisis?

References

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    • [3] C. Coleman. "Turbocharger History." Renault 5 GT. Internet: http://freespace.vir​gin.net/c.coleman/tu​rbhist.htm [Feb. 25, 2007].
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    • [9] D. G. Tadokawa. "Turbocharging Basics 101." Internet: http://www.mazdausa.​com. Path: Mazdaspeed;Mazdaspee​d Vehicles; 2003 Mazdaspeed Protege, [Feb. 25, 2007].
    • [10] M. Ebisu et al. (Feb. 2004). "Mitsubishi Turbocharger for Lower Pollution Cars." Technical Review. [On-line]. 41.1, pp. 1-3. Available: http://www.mhi.co.jp​/tech/pdf/e411/e4110​40.pdf [Feb. 25, 2007].
    • [11] A. Potter. (Feb. 2007). "Planet-friendly Design? Bah, Humbug." Maclean's. 120.5, pp. 14. ProQuest. U of Southern CA Lib, Los Angeles [Feb. 25. 2007].
    • [12] Yahoo! Movies. "The Fast and the Furious: Tokyo Drift (2006)." Internet: http://movies.yahoo.​com/movie/1808715999​/photo/615955, [Feb. 26, 2007].
    • [13] Pippin, Matthew. Your Dictionary. Internet: http://www.yourdicti​onary.com/images/ahd​/jpg/A4piston.jpg, [Feb. 21, 2007].
    • [14] "Turbo Diagram." J&H Turbo Service. J&H Diesel Service. 22 Feb. 2007 Internet: http://jhdiesel.com/​turbochart.htm, [Jan. 23, 2007].