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Old 04-23-2009, 07:42 AM   #1 (permalink)
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Smile modifying the diesel for more economy

Hey, guys, i didn't read all the threads but has anyone allowed the boost to occur normally but defeated the ability of the injection pump to add more fuel as the boost increases? Depending on the type of pump prevent the pump from knowing that the boost went up. Just a thought. And if cooling the fuel gets you more horsepower will heating the fuel get you more mileage? When using exhaust temperature to optimize timing, is the lowest temp. on the advanced side of TDC the best or the highest temperature?

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Old 04-23-2009, 08:47 AM   #2 (permalink)
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heated fuel yes...

I suspect though, if you tried to lean out your injector pump your EGTs would go through the roof and cook your turbo. I'm gonna say no, unless you wanted to invest in watermethanol injection/etc to bring them back down.

What kind of vehicle? On the VW TDI engines, you can chip them... while it gives the engine more power/performance, if you keep your foot off it (drive it normal, hypermile would probably make a huge difference), its been reported to increase efficency by 5-10% (hypermiling would likely do even more) due to better timing and mixture.

If I had to guess, without knowing your engine/enginemanagement... timing, timing will have the greatest single effect you can do without external modifications (chip, water-meth, etc)
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Old 04-23-2009, 09:39 AM   #3 (permalink)
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Quote:
Originally Posted by diesel_john View Post
Hey, guys, i didn't read all the threads but has anyone allowed the boost to occur normally but defeated the ability of the injection pump to add more fuel as the boost increases? Depending on the type of pump prevent the pump from knowing that the boost went up. Just a thought. And if cooling the fuel gets you more horsepower will heating the fuel get you more mileage? When using exhaust temperature to optimize timing, is the lowest temp. on the advanced side of TDC the best or the highest temperature?
What you are asking is can the diesel ECU be re-mapped. If you re-map it then you can tell it to put in less fuel than there is air. It gives you lean burn. Downside is you sacrifice power. With lean burn your going on you're going to want regular temp fuel not warm.

The warm fuel will evaporate easier and the temps will climb faster(as there is less fuel overall per air(the fuel in direct injection engines cools the charge to allow for higher compression without pre-detonation)). If you take away some of the cooling ability of the fuel you run ugly risks.

Yes the HF only goes lean-burn when everything is warm, but its not DI. Its compression is nowhere near so aggresive as a DI engine so it doesn't matter there. In your diesel heating the fuel and leaning out I predict would have neutral benefits because the engine is going to try and counteract you to avoid pre-ignition.

If you just change the ECU and leave everything else alone you'll see an increase in FE, but a pretty drastic decrease in power. What you really want is an onboard system that allows for 2 maps. One for normal driving and one for ultra-lean/lean burn. So once you get to speed hit the button and it coasts along at reasonably high rpm with very little fuel getting injected and your turbo cramming air in there.
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Old 04-23-2009, 10:32 AM   #4 (permalink)
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I did it the other way around, added more boost for any given injection quantity through a simple bleed in the pressure line to the ECU. FE went down, probably due to higher back pressure from the VGT vanes.

Fuel in my TDI is being recirculated to the tank. At operating temps the fuel sensor in the injection pump reads around 50 C. I doubt there would be much to gain.

Fuel in a diesel does not evaporate, it atomizes and the small droplets burn. Lean mixtures in a diesel generate lower EGT. Never heard of pre-detonation. how can it predetonates without fuel? Fuel is injected right when it needs to start burning after a very short delay.

Off course I'm talking about a VW TDI with a VGT turbo. If you have a mechanical IDI with a wasgated turbo things might be different a bit.
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Old 04-23-2009, 10:53 AM   #5 (permalink)
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Originally Posted by tasdrouille View Post
I did it the other way around, added more boost for any given injection quantity through a simple bleed in the pressure line to the ECU. FE went down, probably due to higher back pressure from the VGT vanes.

Fuel in my TDI is being recirculated to the tank. At operating temps the fuel sensor in the injection pump reads around 50 C. I doubt there would be much to gain.

Fuel in a diesel does not evaporate, it atomizes and the small droplets burn. Lean mixtures in a diesel generate lower EGT. Never heard of pre-detonation. how can it predetonates without fuel? Fuel is injected right when it needs to start burning after a very short delay.

Off course I'm talking about a VW TDI with a VGT turbo. If you have a mechanical IDI with a wasgated turbo things might be different a bit.
Thats clever.

I'm not sure if diesels do this but GDI does, they have stages of fuel injection for just the reason I mentioned.

Fuel layering allows you to continue to compress the mixture further before heat induced ignition. Its pretty simple and pretty ingenius.

Compres mixture gets hot, inject fuel, ignition.
Fuel Stratification
compress mix gets hot, inject fuel earlier, compress further than in example A, inject, compress, inject, ignite.

Use the same amount of fuel just inject slightly earlier to allow the fuel to evaporate and drop mix temps enough to avoid ignition and allow for further compression at lower octane rating(for gas).

If your diesel doesn't do this the next model year will. If your car/vehicle does this do not increase fuel temps above native temps, otherwise you are impeding your engine.
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Old 04-23-2009, 03:35 PM   #6 (permalink)
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Be careful trying to heat the fuel with a mechanical injection pump. Heating the fuel makes it more compressible which effects injection timing.

The best way to get a higher efficiency with a diesel is to cram more air into the cylinders. This allows more fuel energy to go into heating the combustion gasses and less heat transferred to the engine block. Cooler intake air also helps for the same reason.
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Old 04-23-2009, 04:05 PM   #7 (permalink)
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Quote:
Originally Posted by ConnClark View Post
Be careful trying to heat the fuel with a mechanical injection pump. Heating the fuel makes it more compressible which effects injection timing.

[b]The best way to get a higher efficiency with a diesel is to cram more air into the cylinders. This allows more fuel energy to go into heating the combustion gasses and less heat transferred to the engine block. Cooler intake air also helps for the same reason.[b]
If you take the route tas suggested and lie to your ECU about the amount of air by putting a leak in the line(which you could also do by placing a small butterfly valve with a servo on so you could vary it as you chose) then you should turn all the frontal area of your ride into a mesh covered ram scoop. It will lighten the load on the turbo allowing it to approach free-wheel speeds of 150K rpm or maximum boost at lowest possible temperatures at a lower engine rpm(takes less exhaust gases to turn the turbo if it has to do less work to turn).
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Old 04-23-2009, 09:15 PM   #8 (permalink)
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Smile to clarify just asking about diesels right now

I have a mechanical diesel NA.
tasdrouille seems to have the closest idea to my first question. That being on a turbo diesel when a less fuel to air ratio is forced. Is the mileage any better. Such as when the intake pressure sensing loop is shut off or modified. And so far the consence seems to be that pumping losses offset any gains. at least if you got a VGT.
I have the timing advanced to the maximum vw recommends. i am setting it statically so wondered if there was a rule of thumb to set it by EGT.

Last edited by diesel_john; 04-23-2009 at 11:40 PM..
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Old 04-23-2009, 11:02 PM   #9 (permalink)
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I think the question you are now asking is does FE improve under lean burn?

yes and no. If you can get away with using less hp then yes, because the engine is burning extra air for "free." If you still need more HP (under acceleration) no it stays the same.

Of course if you are highway cruising at constant speed its going to be advantageous.
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Old 04-23-2009, 11:43 PM   #10 (permalink)
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Quote:
Originally Posted by theunchosen View Post
I think the question you are now asking is does FE improve under lean burn?

yes and no. If you can get away with using less hp then yes, because the engine is burning extra air for "free." If you still need more HP (under acceleration) no it stays the same.

Of course if you are highway cruising at constant speed its going to be advantageous.
I'd like to just take out two pistons once i get up to cruising speed, but i haven't figured out how to do that yet.

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