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No pudding until you eat your meat

June 23, 2010
I don’t talk about work a whole lot on here. If I got too specific with some of the kickass stuff I get to do, I’d probably be fired. And frankly, the kickass stuff is usually sandwiched between a bunch of big, fat, boring slices where I’m making spreadsheets, lists, and powerpoint presentations. But here’s something that’s on the plate. This fancy graph from my propulsion book shows you a little of what goes into designing a good turbocharger.
On the y-axis is your compressor’s pressure ratio. This can vary based on what components go into your engine or by varying your altitude and effectively changing your incoming pressure. On the x-axis is a function of your mass flow of air going through the compressor. In design you can change your compressor ratio and change how much air flow you’re letting get through there as well. Typically you’d run some tests and they’d plunk out this neat little graphs. Each line shows how efficient your turbocharger is being. You come up with a baseline like this, then you can increase/decrease your mass flow of air (the easier option) or switch crap around to change your compressor’s pressure ratio. On the left is the “surge line”. You definitely don’t want to be on the other side of that. When you do you get something uncomfortable as seen in this video below. That strange flapping sound is the sound of surge.

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