question about gasoline direct injection theory
Oh ok, maybe we're more on the same page than i thought. True you're not getting anything at TDC, but you would at 5* ATDC, 2*, 1*, one millionth of a degree, etc. So instead of saying 1/infinity degree ATDC, i just said TDC.
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i doubt many people coming into this forum are going to think that instantaneous combustion/pressure exists (and surely you don't believe that anybody in here so far thinks that it does). but even if it did exist, it would not be desirable at 90 degrees ATDC like you mentioned in your point.
Instantaneous pressure would split the cylinder or twist the crank apart. The burn would optimally be timed so max pressure occurred at the 90 degree point.
I understand spray pattern is very important for direct injection.
Jim
I understand spray pattern is very important for direct injection.
Jim
Joined: Nov 2001
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From: LT1 land...the "409" of the 90s!
BTW BMW is a leader in this area. We should be seeing them in the next few year. Fully computer controled valve timing and direct port injection. NO starters 
On The Tree
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From: Fort Worth, TX
BMW actually has direct injection on it's V12 right now. Audi uses it on it's new 2.0T engine and will soon be using it on much more. A no starter engine would be really interesting but I can see it being really hard to do in a cold climate. Another advantage of direct injection is they spray the fuel right at the spark plug so they get a more complete burn. Very cool stuff.
Someone mentioned using multiple sprays to extend the burn; I don't know if this is being used on gas engines but the new Mercedes diesel uses it to make the engine quieter. Not really for power but an interesting tidbit regardless.
Someone mentioned using multiple sprays to extend the burn; I don't know if this is being used on gas engines but the new Mercedes diesel uses it to make the engine quieter. Not really for power but an interesting tidbit regardless.
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From: Sunny London, UK
And as if by magic.. http://ls1-australia.com/forum/viewtopic.php?t=2197
GM's new direct injection engine, looks well cool. Note is is said to run leaner too.
GM's new direct injection engine, looks well cool. Note is is said to run leaner too.
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Audi actually uses it on the 2.0T, and the 3.2 V6, and it will debut for the market in the 4.2 in the RS4. Which has 420hp/420ft/lbs and revs to something like 8000+rpm. Man I can't wait to PDI that one. Audi actually credits there Le Mans wins to DI, or as they call it, FSI, because they are able to run leaner and thereby cut down on total pit stop time needed. We here in the US actually get a different version of DI than those in Europe because of fuel quality concerns. In Europe they use a true stratefied charge, while we here do not get it.
On the topic of delaying the fuel spray until much later in the cycle, it would be very difficult get the fuel to completely burn in an environment with rapidly declining pressures as well. This could cause all sorts of issues with unburnt fuel staying in the cylinder, not to mention, very inefficient. I don't have the specs on when the Audi's spray the fuel in and especially not with there race cars, but I can try and find out.
On the topic of delaying the fuel spray until much later in the cycle, it would be very difficult get the fuel to completely burn in an environment with rapidly declining pressures as well. This could cause all sorts of issues with unburnt fuel staying in the cylinder, not to mention, very inefficient. I don't have the specs on when the Audi's spray the fuel in and especially not with there race cars, but I can try and find out.
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From: Texas
Originally Posted by 01SSRMS
On the topic of delaying the fuel spray until much later in the cycle, it would be very difficult get the fuel to completely burn in an environment with rapidly declining pressures as well. This could cause all sorts of issues with unburnt fuel staying in the cylinder, not to mention, very inefficient. I don't have the specs on when the Audi's spray the fuel in and especially not with there race cars, but I can try and find out.
So far, my reading of some of the technical info published is that the gasoline must be injected before the cylinder reaches full compression, as you mention, due to the fact getting it to burn in a cylinder dropping pressure is a problem and the burn isn't complete(higher emissions).
Has anyone seen the fuel pressure specs being used for GDI engines? I am wondering what the injector flow rate works out to be, as the fuel pressure has to be very high.
Todd
Todd--- You sparked my curiosity on what the actual rail pressures on our Audi's run. Found a tech book that says 50-110 bar, which works out roughly to ~720-1600 psi. It uses the same setup that most DI motors use, which is a normal electric in tank pump, and then a step up pump run off of the cam shaft, just before the fuel rail. So yes, I would consider that fairly high pressue, though nowhere near what the diesel trucks are running, I believe ~15000psi and higher.
Trey- I'm far from being enough of an expert on combustion cycles to really make a good point. But in order to have the same pressure at 90* ATDC as we normally run right at TDC you would have to have ridiculously high compression, which would sap alot of power just to build on its own. Then you have to realize that fuel does not burn instantaneously. It's quick, but it does take a few milliseconds to burn across the top of the piston when it is near TDC. Just think if you increase that volume 4x (rough estimate of volume of cylinder when piston is at 90*ATDC, then it takes 4x longer to burn, the burn will be much much less complete equalling much less power, if you could even get it to run, which would be a feat to accomplish.
Trey- I'm far from being enough of an expert on combustion cycles to really make a good point. But in order to have the same pressure at 90* ATDC as we normally run right at TDC you would have to have ridiculously high compression, which would sap alot of power just to build on its own. Then you have to realize that fuel does not burn instantaneously. It's quick, but it does take a few milliseconds to burn across the top of the piston when it is near TDC. Just think if you increase that volume 4x (rough estimate of volume of cylinder when piston is at 90*ATDC, then it takes 4x longer to burn, the burn will be much much less complete equalling much less power, if you could even get it to run, which would be a feat to accomplish.
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Originally Posted by treyZ28
back to basics- if you had the same pressure you have now only about 70-80* later, it wouldnt be a good thing?
no, it wouldn't be a good thing. not trying to be rude, but do u actually read responses?
yes, it is quite clear that your point is that the best leverage is applied at 90 * ATDC. no, that one simple fact does not outweigh the many many other negatives. u even contemplating this situation is ignoring many facts about combustion and combustion engines.
there's a reason the big boys aren't posting in this one. it's speculation, and bad speculation at that. it was a fine thought, but it got shot down immediately and that should have been the end of it.
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dont some BIG deisels run indavindual electric (72volt!!!) pumps ontop of each injector? well thats what some trunk mechanic told me!
i understand that higher fule rial presures give better atomisation in a normal engine (not dircet injection) and thus more power. is this true for Direct injection motors aswell?
Chris.
i understand that higher fule rial presures give better atomisation in a normal engine (not dircet injection) and thus more power. is this true for Direct injection motors aswell?
Chris.
Teching In
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From: Germany
I only know of mechanical individual pumps on top of injectors. Rigs and some current VW/Audi TDI's use that system. A cam lobe acts upon the pump, which produces close to 30k psi and supplies a piezo injector:
