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Old 04-04-2009, 08:45 AM   #2 (permalink)
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Join Date: Nov 2008
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Hi Liam and welcome,

I'm GLAD YOU ASKED! Its called GDI, Gasoline Direct Injection. Its touted as really high-tech stuff. . .but its been around for over a hundred years and diesels already do it.

With GDI you can have both. You can advance timing substantially because the liquid fuel flashes to a gas when it is injected in the high pressure/temp cylinder. This consumes enormous amounts of BTUs strictly in the form of heat. So it dramatically cools the charge allowing the compression to continue again once the fuel is injected. Normal II Indirect Injection has to stop at 14 degrees below TDC otherwise the fuel can knock, preignite and really terrible combinations of the two.

Ford touts its DIE ecoboost is 30% more gas worthy than normal. If thats true then seeing normal sedans get clear of 50 mpg will be standard and the advantages of diesel over gas will lose alot of leverage.

The advantage to the system is to make sure the fuel injection is controlled almost strictly by your foot on the gas pedal and has nothing to do with the throttle body. Then you rip the throttle out and run Wide Open Throttle all the time and get learn burn and substantially better FE below ~4500 RPM.

You probably know but for anyone who doesn't its like you get to burn as much oxygen(it burns aggressively on its own, cylinder pressure and temperature are almost high enough to ignite it on its own) as you would at WOT, but you're only putting in 1500 rpm's worth. 3x more air to burn(which is pretty free excluding pumping losses) fuel now burns much more aggressively as well. alot more power than you would get out of normal cycle at 1500 rpm, but not as much as you would at 4500. It comes out as getting about 20% more power of free air. . .or 20% less fuel however you wanna look at it.

Making it. . .Drill a plug for a spark plug in a diesel engine and get an ECU you can program and rip your throttle body off. As long as your state does not have laws against custom builds and emissions you should be good to go. GDI has very low emissions to start with especially if the fuel air ratio is above 30:1, so you shouldn't be terribly worried about that. 3-way cats are ineffective against its emissions because its much more like a diesel's exhaust (NOx) than gas(Hydrocarbons).
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