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Written by Devin Durham
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Thursday, 24 May 2007 |
A conversation that I had a couple of weeks ago with Flyin Hillbilly
about exhaust systems and how much energy is being wasted by your motor
pushing heat and gas around reminded me of this short video that I made
in order to illustrate this exact point.
This is a Stirling Engine. It is the most efficient piston engine made by man, and it runs entirely on heat and tendency of gas to both cool and increase density when expanded. Certain examples of this engine are capable of running on the difference in heat between the palm of your hand and the surrounding air.
My little Stirling motor requires about a 250 degree temperature difference. This video should show you how much mechanical power just that little bit of heat (about what a candle puts out) is capable of producing.
This is a very very simplified version of how the engine works: A Stirling engine is entirely a closed system, there is no intake or exhaust. The cylinder is heated, causing the air inside to expand and driving the piston outward, much like a gasoline engine. The expanding cylinder volume causes the air to have to expand to fill the increased volume (that being the nature and definition of a gas) and doing so causes it to cool. This colder air then naturally becomes more dense, and contracts... causing the piston to come right back to starting position. A Stirling motor makes as much power on its outward stroke as it does on its inward stroke.
But what does this have to do with street cars? Well when you watch the video, understand that this entire motor is about 2 or 3 cubic centimeters in displacement, and the temperature difference being added to the cylinder is about 250 degrees... now imagine your exhaust system, running at 1,400 degrees and displacing many cubic liters of space and you might begin to see how significant an increase in volume and a loss in exhaust temperature can be. A Stirling motor shows us graphically how it can be that 1/3 of a car engine's power is expended doing nothing other than pushing gas around.
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Last Updated ( Thursday, 24 May 2007 )
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