Author Topic: Auto Tech: Direct versus port fuel injection  (Read 6212 times)

Offline Autos_Editor

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Auto Tech: Direct versus port fuel injection
« on: October 19, 2011, 04:03:21 am »


Many new cars advertise that they have direct fuel injection, but what exactly is it?  Technical Editor, Jim Kerr, explains.

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Offline Gardiner Westbound

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Re: Auto Tech: Direct versus port fuel injection
« Reply #1 on: October 19, 2011, 05:26:02 am »
Gasoline direct injection (GDI) is not quite ready for prime time technology. Severe issues include high pressure fuel pump failure, gasoline diluted oil, carbon build up on intake valves and excessive noise.

Let adventurous early adopters with deep pockets take the hit for the team. Prudent individuals wait for new technology to mature and prices to moderate. Less costly, lower tech cars markedly reduce exposure to dissatisfaction, expensive repairs and replacements.
« Last Edit: October 19, 2011, 05:41:19 am by Gardiner Westbound »
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Offline tpl

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Re: Auto Tech: Direct versus port fuel injection
« Reply #2 on: October 19, 2011, 05:53:37 am »
Gardiner I guess you'll be checking your dwell and adjusting your carb's this weekend then?    ;)   :o

DI has worked for diesels for a long time.

I do not understand why DI would cause gas in the oil any more than bad compression in any other engine.  I also do not see or hear any excessive noise although I'd agree that the noise on idle when the engine is cold ( on my GTI) is of a different tonal quality from some previous 4 cyl FI cars.
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Offline nlm

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Re: Auto Tech: Direct versus port fuel injection
« Reply #3 on: October 19, 2011, 08:32:31 am »
Does DI also increases the amount of 'gunk' around the injector and require more maintenance?

Offline ktm525

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Re: Auto Tech: Direct versus port fuel injection
« Reply #4 on: October 19, 2011, 11:04:50 am »
A LR tech was telling me that the new DI 5.0L Jaguar V8 was having issues with carbon build up and injector issues. He advised me to stick to the 4.4 until they get things sorted.

Offline safristi

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Re: Auto Tech: Direct versus port fuel injection
« Reply #5 on: October 19, 2011, 11:36:34 am »
rumour and conjecture wot the interWEB woz made fer..............

have ya heard :foil: ......Bee ESS   Bee ESS..................


Pee ESS  i'm using the CARBON from My direct injection engine to heat the whole house this Winter......... :stick:
Time is to stop everything happening at once

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Re: Auto Tech: Direct versus port fuel injection
« Reply #6 on: October 19, 2011, 04:03:44 pm »
carbon buildup on GDI depends on engine design .

GM does not suffer on the GDI V6, neither does Porsche on the flat sixes. The same can not be said about VW/Audi.

http://www.autoobserver.com/2011/06/direct-injection-fouls-some-early-adopters.html

http://www.audizine.com/forum/showthread.php/336352-Audi-FSI-Engine-Carbon-Build-up-Megathread

http://forums.quattroworld.com/rs4b7/msgs/34557.phtml

http://www.audiforums.com/forum/b7-models-71/carbon-buildup-intake-valves-new-a4-113568/

Hi-press fuel pump failure can happen to anyone, really.



Offline HeliDriver

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Re: Auto Tech: Direct versus port fuel injection
« Reply #7 on: October 19, 2011, 07:07:00 pm »
I'm not overly concerned about the carbon build-up issue. I considered adding a catch can to eliminate the problem, but it's just not worth the hassle IMO. Worst case, I figure I'll have to pay $500-1000 to have the valves and intake runners cleaned once, maybe twice while I own the car. I can live with that if it comes to it.

I also understand that VW has improved the PCV system on the new TSI engine to reduce the amount of oil that gets fed back through the intake. I guess we'll see.

As for the gas in the oil, my understanding is that having the fuel injected directly into the cylinder makes it more likely for fuel to condense on the cylinder wall and drip past the rings. But, the only way I can see that happening is on shutdown, and I can't imagine why the engine computer wouldn't cut the fuel a fraction of a second before it cuts the spark to make sure it all gets burned.

Offline rrocket

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Re: Auto Tech: Direct versus port fuel injection
« Reply #8 on: October 19, 2011, 07:27:19 pm »
Gasoline direct injection (GDI) is not quite ready for prime time technology. Severe issues include high pressure fuel pump failure, gasoline diluted oil, carbon build up on intake valves and excessive noise.

Let adventurous early adopters with deep pockets take the hit for the team. Prudent individuals wait for new technology to mature and prices to moderate. Less costly, lower tech cars markedly reduce exposure to dissatisfaction, expensive repairs and replacements.

Lexus' design of the D4S dual injection system (using both port and direct injection) is a proven design since 2006.  It has worked flawlessly and doesn't suffer from any of the negatives of some of the direct inject engines of the competitors.

"As described in the January 2006 issue of SAE Automotive Engineering International, the system primarily relies on the port injection system when low engine speeds are combined with high loadings. Under these conditions, a direct injection scheme cannot properly atomize the fuel, and so approximately 60% of the fuel is provided by the port injector. As engine speed increases, the direct injection system takes over more of the fueling responsibility, until eventually it provides 100% of the necessary go-juice. Obviously, there some complex calculations going on to determine the optimum fueling over the engine's operating range, and that has led to over 300 patents being issued to Toyota concerning the design of this system.

There's a 7% increase in HP and 7.5% increase in torque from the system, some of which comes from the 11.8:1 compression ratio that's enabled by the use of direct injection. Better yet, the benefits apply to the entire powerband, so this is a feature that will be useful to most any driver.

The dual injection system also reduces cold-start emissions. The port injection system dumps a bit of fuel on the back of the closed intake valve; when that valve opens, the fuel is evenly distributed throughout the cylinder. As the piston approaches the top of its travel, the direct system injects a bit more fuel into the cavity on top of the piston. The total air/fuel mixture in the combustion chamber is slightly lean, but the mixture is significantly richer in the area around the spark plug, making it easier to ignite in a cold engine. The result is quicker warm-up and smoother operation when cold."

You can see cut-aways of where the injectors are in the engine. One in the intake runner (port) the other in the cylinder (direct injection)

How fast is my 911?  Supras sh*t on on me all the time...in reverse..with blown turbos  :( ...

Offline windstarguy

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Re: Auto Tech: Direct versus port fuel injection
« Reply #9 on: October 19, 2011, 10:33:07 pm »
Interesting article, thanks!

Offline Seafoam

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Re: Auto Tech: Direct versus port fuel injection
« Reply #10 on: October 20, 2011, 04:49:44 pm »
And is this why honda and toyota haven't adopted direct injection yet in their mainstream vehicles yet? ;)
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