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TDI Fuel Economy Discussions about increasing the fuel economy of your TDI engine. Non TDI related postings will be moved or removed.

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Old November 12th, 2009, 13:30   #61
GoFaster
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The complicating factors here are the turbocharger, and the fact that the air/fuel ratio is not constant like it is with a gasoline engine.

On a non-turbo gasoline engine, the torque curve is essentially the volumetric-efficiency curve (at full load). The engine makes the most torque at the RPM where it breathes the best. And to change that ... you change the camshaft (or the intake and exhaust tuning).

This approach works on gasoline engines. Installing a different camshaft and sorting out the intake and exhaust tuning on my little Honda CBR125R cut normal fuel consumption from 3.2 - 3.3 L/100 km to around 2.9 - 3.1 L/100 km and it makes more power, too - necessary when you are only starting with 12 horsepower.
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Old November 12th, 2009, 16:32   #62
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GoFaster, what about with a turbo/super gasser?
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Old November 12th, 2009, 19:15   #63
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It becomes complicated and you can't draw any inferences about engine efficiencies from the torque curve, because the turbocharger masks the natural breathing characteristics of the engine itself. A lot of modern turbo gas engines have an artificially limited torque curve. VW/Audi is notorious for this! They brag that the engine makes (almost) the same torque over a wide RPM range ... and it's because it's artificially limited to that torque.
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Old November 13th, 2009, 11:53   #64
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Quote:
Originally Posted by McBrew
Meister... good points about the losses. I was intrigued by a system I read about that used regenerative braking... but by using hydraulic pumps/motors at the wheels to compress gas (over oil) in high pressure cylinders while braking, and then use that system in reverse to recover the energy while accelerating. This would be, of course, in conjunction with an ICE or electric drive. The efficiency, according to the article, was much greater than electric regenerative braking. I'm sure you've heard of this, but I'm mentioning for the benefit of others reading this thread.
I was just about to post about this when I saw your post. From what I have read, or about the vehicles I have read about. It does not use an electric motor, it uses hydraulic motor, or motors. The two applications I have read about this being used is in garbage trucks and UPS delivery trucks. I am no expert, but I would prefer to own a vehicle with this type of system vs an all electrical one that realys on an expensive and heavy battery pack.

Also, as long as we are talking about types of hybrid systems, I also read about a moto GP bike using a type of flywheel that would spin up to 50,000 rpms under breaking, then use the stored energy to help accelerate out of the corners. The cool part of this was, the bike was under the minimum competition weight, so instead of adding balast, they added this system, I think I read that it reduced lap times by .2sec or somthing like that. Neat idea though.
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Old November 13th, 2009, 14:53   #65
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Cool, glad this thread got revived. Thanks for the BSFC chart post chewy! Impressively large area of max efficiency for that V12. Of course, it makes so much power you'd hardly ever be up in that region of operation... 1000 N-m !!!!

RockyRunner, as others have alluded to, engine breathing is generally optimal in a specific (small) rpm range. However, perhaps the most important factor to keep in mind when considering this, is that internal engine friction losses increase with rpm... period. You WANT your best breathing/combustion to be at a low rpm to extract max efficiency. However, when you go too extreme with this. you really run out of steam at the top end, and the result is a fairly low HP rating and lethargic acceleration. Think geo metro, or heck, even our own ALH TDI. When you re-tune to get the most power possible out of a given setup, you generally end up with a peakier torque curve.

Yeah, hydraulic series hybrids are where its at! Especially for stop/go delivery trucks. You get so much of your energy back when you slow down.

Formula one has been experimenting with a mechanical flywheel energy capture system, called KERS (kinetic energy something something... regenerative system maybe?). They spun up a small heavy flywheel to some crazy rpm and then can hit a button to couple it back to the drivetrain for a short burst of power. Pretty cool.
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Old November 13th, 2009, 21:47   #66
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Is that the BSFC plot for the ALH? The plots that Shizzler discussed seem like it fits a ALH tdi application except everything to the left of 1500 rpm. If you take your tdi and put it in 2nd or 3rd gear at 1000 rpm it most certainly doesn’t behave as if it had a 1200# horse hitched to it pulling; more like maybe 2-3 less than athletic guys trying to push it. Bear in mind that 1 hp at 1000 rpm is about 5 ft lb. I question if the ALH will produce 20 newton meters at 1000 rpm. If we accept this as a legitimate ALH tdi plot then we should have about 30 newton meters of torque at 1000 rpm. My tdi idles at approximately 1000 rpm where the engine is barely producing enough power to keep itself turning.
Who in his right mind would record or plot where the “400” and “500” g/kWh run so close together? Obviously the engine was having trouble producing power despite large amounts of fuel at that point. This couldn't have been done by technicians/engineers. It seems to me that this “picture” which does appears to be a typical bsfc plot was produced by artists on Madison Ave who extended the lines to the left of 1500. Someone pretty gullible sucked it up and posted it here at tdi.com.
If this plot is for a ALH then the left should start at 1500 maybe 1399.14159265… but certainly not 1000 rpm. If the axis starts at 0 or any rpm <1399-1500 the line representing the engine should not extend past 1400-1500.
How did this plot come to be accepted by tdiclub.com as a legitimate plot for a ALH?
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