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Old 09-13-2012, 09:59 AM   #91 (permalink)
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Originally Posted by DieselCAR View Post
The VW TDI turbo diesels cut injection quantities to next to nothing when in gear going down hill - (with your foot off the accelerator). Even more efficient than coasting out of gear with the engine idling.
It seems that there should be some way to use this same technique in your truck when there is no demand on the engine.
UFO -
Actually it's not more efficient than coasting with the engine on, there is significant engine braking that costs momentum when the fuel is cut.
Maybe this behavior is unique to TDI's. On a significant downhill grade I can shift into 5th and have very little engine braking effect - and the electronics basically cut off fuel to the engine. When the RPM's get down to around 1250, the controller starts feeding fuel to the engine again.
So implementing this behavior electronically, or some type of start/stop technology, when the engine has no load should be beneficial.
Even better of course would be some form of regenerative braking. This is where even a small battery pack might be very useful - in helping to keep the start/stop or electronic injection from needing to cycle as frequently.

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Old 09-15-2012, 08:36 PM   #92 (permalink)
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Originally Posted by DieselCAR View Post
Maybe this behavior is unique to TDI's. On a significant downhill grade I can shift into 5th and have very little engine braking effect - and the electronics basically cut off fuel to the engine. When the RPM's get down to around 1250, the controller starts feeding fuel to the engine again.
So implementing this behavior electronically, or some type of start/stop technology, when the engine has no load should be beneficial.
Even better of course would be some form of regenerative braking. This is where even a small battery pack might be very useful - in helping to keep the start/stop or electronic injection from needing to cycle as frequently.
Or instead of batteries, very large capacitors?
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Old 09-15-2012, 09:21 PM   #93 (permalink)
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Diesels do spin more freely because they have no throttle. So coasting in gear may be a good idea, particularly if a little engine braking is needed anyway. But, another advantage diesels have is they use virtually no fuel at idle, so, if max coasting is desirable and you are not comfortable with EOCing, you are better off dropping it into neutral and coasting engine on.
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Old 09-15-2012, 11:16 PM   #94 (permalink)
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Diesels do spin more freely because they have no throttle. So coasting in gear may be a good idea, particularly if a little engine braking is needed anyway. But, another advantage diesels have is they use virtually no fuel at idle, so, if max coasting is desirable and you are not comfortable with EOCing, you are better off dropping it into neutral and coasting engine on.
Huh? Exactly how to they work if no throttle?

If they use virtually no fuel at idle, how come a local heavy equipment operator I know is going broke since he says his big Cat diesels burn ~6 gallons/hour just idling?
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Old 09-16-2012, 03:15 PM   #95 (permalink)
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They regulate fuel flow only, the air intake is always unrestricted.

"Virtually" no fuel means relative to what a gas engine of equivalent size and power would use at idle. And ~6 gallons sounds way off. More like ~1 gph.
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Old 09-16-2012, 03:36 PM   #96 (permalink)
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Originally Posted by JacobAziza View Post
"Virtually" no fuel means relative to what a gas engine of equivalent size and power would use at idle. And ~6 gallons sounds way off. More like ~1 gph.
When I drove a school bus, most of our fleet did not have air conditioning, unless they were for Special Needs or sports, but if we had it, we usually kept the bus running while waiting. One day pamphlets from the AZDOT showed up telling us that an idling engine consumed as much fuel as one powering a vehicle traveling seventy miles an hour.

None of us believed it. One driver said that he had idled for two hours recently and it had not used anything.

I believe that is called perpetual motion or magic.

One GPH sounds reasonable, even for a large engine.
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Old 09-16-2012, 04:36 PM   #97 (permalink)
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My tdi uses about a gallon of gas at 55-60 mph at idle it should use around 1L an hour.With a semi truck i could see it consuming a gallon of diesel an hour at idle.
4 x what the tdi uses at idle seems reasonable
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Old 09-16-2012, 05:25 PM   #98 (permalink)
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tractor trailer gap - why not rounded front?

Just out of curiosity - Why trailers do not use rounded front? When the curvature is made with radius of the same length as the distance from peg to front corner, it should help aero performace. It doesn´t increase overall tractor trailer gap as peg to corner distance needs to be kept anyway for sharp turns. Am I wrong?? Not much trucks or truckers in place where I live...
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Old 09-17-2012, 12:20 PM   #99 (permalink)
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... We will have an air bladder that inflates at 35 mph and deflates very quickly below that speed. It will seal up that gap tighter than a bulls rear-end in fly season.
Truly clever.

My first car didn't even achieve the mpg your truck is getting! It was a '71 LTD Squire Wagon, 400 CiD, about 11 mpg.

I work in East Hartford, not far from your Newington location.
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Old 09-17-2012, 01:14 PM   #100 (permalink)
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Just out of curiosity - Why trailers do not use rounded front? When the curvature is made with radius of the same length as the distance from peg to front corner, it should help aero performace. It doesn´t increase overall tractor trailer gap as peg to corner distance needs to be kept anyway for sharp turns. Am I wrong?? Not much trucks or truckers in place where I live...
I was thinking that myself just the other day. I think the reason is that various regulatory agencies regulate the length of trailers. They get the most efficient use of their space by having square corners all way around. It would be nice if the agencies would go along with your suggestion since it is more efficient and poses no more effective length and no safety hazards. Maybe someone will do it.

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