DI Engine should use Cheap Gas!

[MisterJJ]

I would like to propose that a direct injection engine should use cheap gas.

Direct injection engines have the fuel delivered directly to the combustion chamber. Because of this the fuel does not wash over the intake valves and does nothing to keep them clean. Additionally, the fuel being sprayed against the cylinder walls appears to contribute to these engines having a high degree of fuel dilution in the oil.

Top tier gas is praised for the additives it contains. These additives keep the intake valves clean on engines that don’t have direct injection and they also keep the injectors clean. So these additives remove deposits from intake valves, right? What are these deposits? Well, it’s mostly oil from the PCV system or oil dripping down from the valve guides. So the gas additives dissolve the oil that would normally build up on the intake valves. But in a direct injection engine the intake valves are not being exposed to these additives and we also have a problem with the fuel getting into the oil. What are these additives doing to the oil in the engine? I don’t know but it seems reasonable to conclude that additives designed for dissolving oil is not a good thing to add to your oil.

Therefore, I would propose that the best thing to do for a direct injection engine is to use the cheapest fuel available which would have the least amount of harmful additives. The occasional use of specialty fuel injector cleaner added to a tank of gas would be required to keep the injectors clean. Yes, some of that would get into the oil, but it would be much less than if the additive laden top tier gas was always used.

What do you think?

 

[bepperb]

Interesting, it makes sense.

Soon enough, SN oil will come to help with these issues, primarily staying in grade and basic when dilluted with the ethanol, which for the same reasons will find it's way into the oil often on these engines.

 

[addyguy]

I understand your logic, but I think it is flawed.....

You want a high-quality fuel to not only keep the injectors clean (as you alluded to), but you also want the fuel to burn cleanly, so you don't get carbon build-up on the pistons and rings. A poor-quality fuel wouldn't burn 'cleanly', and contribute to deposits.

Also, you want a higher-quality fuel so there is less chance of their being 'debris' in it, so you don't clog fuel filters or the very finely calibrated injector nozzles, as mentioned.

Finally, DI alows for the use of higher compression to make more power. You want a high-quality fuel to guarantee there will be no knock or ping.

By 'high quality' I don't necessarily mean highest octane, I just mean a 'quality' fuel from a known station, as opposed to complete no-name 'junk'....

 

[d00df00d]

to BITOG!


That argument seems plausible on the surface, but there are three problems:

1. You keep making comparisons -- more than this, better than that, worse than the other thing -- without numbers or facts. You need something solid before you can make an argument. For example, you say the harm of a shock treatment of fuel injector cleaner is less than the harm of a steady diet of additive-rich fuel. I'm sure you can see how that could go either way depending on a lot of factors.

2. All good engine oil has cleaning additives. Does that necessarily mean we should all switch to non-detergent racing oil? Cleaning additives are not necessarily harmful just because they are cleaning additives. Esters are a great example of a kind of substance that has cleaning and protective properties. Even if an additive is potentially harmful to oil, the net effect might be better. For example, a steady diet of high-detergent fuels will help keep the combustion chamber clean, which would help maintain efficient combustion, which could lead to less fuel dilution.

3. There are some modern cleaning agents that are designed to survive the combustion process. They can then help clean the intake by escaping into the crankcase and exhaust and then being re-breathed into the intake through the PCV or EGR.


Hope that helps.

 

[Carbon]

I think fuel additives clean the fuel injectors and combustion chambers. http://www.chevron.com/products/prodserv/additives/tcp.aspx

 

[Boomer]

Gasolinje all comes from the same source in a given geographical area. Trucks all fill up at the same site but the additives for different brands are added at the turck. So the fuel (base) is the same. Only the additive package differs.

 

[MisterJJ]

Originally Posted By: d00df00d
You keep making comparisons -- more than this, better than that, worse than the other thing -- without numbers or facts.


You mean like this:
Originally Posted By: d00df00d
Even if an additive is potentially harmful to oil, the net effect might be better.


Originally Posted By: d00df00d
You need something solid before you can make an argument.

Is this your first day on the Internet. ;-)
I'm just looking to start a discussion on this and hopefully the facts will eventually come to light.

Originally Posted By: d00df00d
There are some modern cleaning agents that are designed to survive the combustion process. They can then help clean the intake by escaping into the crankcase and exhaust and then being re-breathed into the intake through the PCV or EGR.

Which brings up a further point that using a catch can will possibly make the valve situation worse because it takes away a certain amount of fuel along with the oil and other gunk. That fuel might help keep the valves cleaner than they would be with the catch can.

 

[d00df00d]

Sorry man, didn't mean to spook you. Good luck.

 

[MisterJJ]

Originally Posted By: d00df00d
Sorry man, didn't mean to spook you. Good luck.


No worries. I'm a noob here but I've been an occasional lurker here and I am a regular on a few automotive forums for several years. I've got a pretty tough I-Skin.

I'm just a bit flustered to discover that my Audi 2.0t direct inject engine, which I love, is turning out to be prone to several serious problems. Not only does it choke itself on intake deposits from weeping valve guides, but it sheers oil, contaminates the oil with fuel, and blows out the cam follower for the high pressure fuel pump along with possibly the pump and the intake cam.

So I'm investigating all possible ways to reduce, if not eliminate, these issues.

 

[Nederlander75]

I once had the same thought of using lesser cleaning fuels for my DI app. However, after Shell's Nitrogen kickoff adn the promise that the adds will survive the combustion process making their way to the intake, valve, and PCV system. Additionally, with these more thermally stable adds getting into the oil they will no doubt aid in its cleaning ability as well as do their job in the intake as the oil is consumed. Additionally, Shell's adds also leave a protective film behind that will help lubricate even in the oil. Obviously not as effective as the oil, but better than just nasty fuel.

 

[Quattro Pete]

Originally Posted By: Carbon
I think fuel additives clean the fuel injectors and combustion chambers. http://www.chevron.com/products/prodserv/additives/tcp.aspx


They can only clean those areas that are washed off by flowing gasoline. Since in a direct injection engine the gasoline does not wash over the intake valves, hence fuel additive will do nothing to clean them.