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Old 12-18-2009, 09:52 AM   #31 (permalink)
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Quote:
Originally Posted by dcb View Post
ok, well in answer to the original question (and the title of this thread), it is as I described, load up the hill at bsfc peak and glide down and glide crawl over the top so you brake less.

Maybe we should change the thread title to "Hills (most efficient climbing technique for diesel / manual transmission after I put a whole bunch of conditions on it)"
Could one of you who knows what you're talking about maybe enter a little more about what BSFC is onto the ecomodder wiki entry, for us that don't have a clue about physics/mechanics?

This sounds like a pretty important concept to learn


edit: never mind, i just looked at wikipedia
edit again: just read the article, have not a clue what it means
edit #3: great article here

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Last edited by Burnt; 12-18-2009 at 10:02 AM..
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Old 12-18-2009, 03:22 PM   #32 (permalink)
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Actually I look at it differently. Here is my example.

Take an engine that has no throttle plate and produces 20 horsepower (under load) at sea level, then move it to a higher altitude.

As the atmospheric pressure becomes lower the power developed becomes lower, regardless of the fact that there is no throttle plate.

At a certain altitude depending on the mechanical compression of the engine, the atmospheric pressure becomes so low that there is not enough compression for combustion to occur.

You control the power developed by gasoline engines by restricting the atmospheric pressure. The pressure available for compression, in the cylinders, is the difference between the atmospheric pressure and the manifold vacuum.

Diesel engines are different, because they will run with very lean mixtures, compared to throttled gasoline engines, which require a specific range of air-fuel ratios to run properly.

Regardless of whether the engine is gasoline or diesel, the power developed is directly proportional to the available air pressure that enters the cylinders to be compressed and ignited.

I call this effective compression.

BSFC is (at 2000 RPM typically) a direct relationship with effective compression. The higher the effective compression the more efficient the engine. Supercharging increases effective compression by increasing the available pressure beyond atmospheric.

Without supercharging aircraft engines lose power at altitude, supercharging restores lost effective compression at altitude.

It's not so much the energy required to pull air past a throttle plate that creates inefficiency as it is the lower compression available due to throttle restriction.

I used the diesel example to illustrate the point about atmospheric pressure reduction creating lower available power at the same RPM.

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Old 12-18-2009, 03:38 PM   #33 (permalink)
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Diesels have no throttle as they are fuel controlled - more fuel, more powah.

They need compression to ignite the fuel - higher compression means air heats up to super temps and fuel ignites as it is injected.

In older engines the injection took place in one go from a mechanical pump. In more modern engines injection takes place over lots of phases - a little bit at the start to heat things up, the power bit (depending on pedal position, engine speed etc.), and then a little bit later on to deal with anything left over - to reduce emissions.

The timing and volume of these depends, as I tapped and as I understand it, on loads of variables (the map) - engine temp, engine speed, pedal position, turbo boost, fuel quality, zodiac position - all sorts.

But I think lugging is basically when the engine makes less on the power stroke than is needed to maintain rotation speed.

Maybe I have this wrong.
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Old 12-19-2009, 12:20 AM   #34 (permalink)
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I lug my gasser I6 down to 800 rpms basicly idleing, in 5th gear 25-30 mph and its happy as long as its flat. I can maintain 15 in of vac and pull in 30+ mpg (mpguino)
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Because we are big dumb redneck Americans and we only want V8s that thunder and use lots of gas pushing our empty Super Duties down the highway at 100 MPH in the fast lane while warming our butts in heated leather seats and chowing down on double quarter pounders and texting on our cell phones. We cant understand non-V8 engines because that ain't whut NASCAR uses...
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Old 12-19-2009, 06:59 PM   #35 (permalink)
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Quote:
Originally Posted by Christ View Post
As I learned it, lugging is defined as the point in the engine's power curve where it doesn't make enough power at full throttle to maintain your current vehicle speed. This would make the lug-point dynamic, not static.
My father's truck "lugs", (audible detonation, timing is almost entirely cut out by the computer), if I give it too much throttle at too low an RPM. Even if it does still accelerate. This generally happens at <2K, above that it does not happen under any conditions. I've held the throttle to the floor in top gear, with the engine spinning around 3K, and it would not accelerate further due to the grade, but it was not lugging.
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Old 12-19-2009, 07:15 PM   #36 (permalink)
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Originally Posted by Arragonis View Post
But I think lugging is basically when the engine makes less on the power stroke than is needed to maintain rotation speed.
I think that's called deceleration.

Now if you meant when the pedal is mashed, that might be a little different story.
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Old 01-28-2010, 01:06 PM   #37 (permalink)
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Quote:
Originally Posted by dcb View Post
ok, well in answer to the original question (and the title of this thread), it is as I described, load up the hill at bsfc peak and glide down and glide crawl over the top so you brake less.

Maybe we should change the thread title to "Hills (most efficient climbing technique for diesel / manual transmission after I put a whole bunch of conditions on it)"
Hi dcb,

Am I right saying that you advise climbing the hill with load above 50% of the accelerator pedal and in the sweet spot of BSFC map (low revs, highest gear and relatively high load)? If yes please correct me if I am wrong in the following:
We start climbing the hill as said above, with lets assume 2200 revs and 2/3 load on the pedal. We are in our BSFC sweet spot. Climbing the hill we start to unload the pedal to lets say 50% and our revs are going down to 1800. Theoretically we should loose torque faster than our fuel consumption is dropping. But what is the real world situation. I thing that when we are lightly unloading the pedal/revs are dropping we will have better fuel consumption than staying under constant load even though we are in our sweet spot.

It went kind a long but hope you understand what I mean.

Your or other opinions are highly appreciated.

Cheers

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