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Old 12-14-2010, 06:52 AM   #231 (permalink)
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Quote:
Originally Posted by NeilBlanchard View Post
Do diesels have Start/Stop tech?
Why not ?
In Europe, it's been on small diesel Citroens and the 3L VW Lupo and Audi A2 since about the time the 1st generation Insight popped up.

10 years on, it's more common on diesels than it is on gas engined cars in the EU market.

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Do the EPA rating for diesels take into account the higher BTU's per gallon of diesel?
Dunno, but on this side of the pond the trend is towards using grams of CO2 per km (which accounts for the energy density) rather than using L/100km or mpg (which does not).

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Old 12-14-2010, 10:05 AM   #232 (permalink)
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Hi,

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Originally Posted by autoteach View Post
So, if the EPA uses mpg for both, but uses mpge for electric, one could conclude that they do not account for the energy density difference. That is their efficiency at constant operation, not using engine stop/start tech.
That's what I figured. According to the X-Prize MPGe spreadsheet, diesel has to be multiplied by 0.9 to be MPGe; or 1 gallon of diesel = 1.12 gallons of gasoline. The Wikipedia page linked earlier says diesel MPG needs to be multiplied by 0.83660305694757009 (!!) to be MPGe.

That makes it seem like most of the FE for diesels is due to the higher energy level of diesel itself, and only a little is because the engines are more efficient.
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Old 12-14-2010, 11:20 AM   #233 (permalink)
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I had a facinating conversation with a guy yesterday who built himself a turbo diesel snowblower (of all things)

He stuck a turbo from a Saab car on it and said a few telling things...

1) it no blows snow WAY further and never EVER bogs down.
2) It burns less fuel overall then before even with the increased power.
3) the black smoke these little diesels are known for is for the most part, gone.

I know how unscientific this is, but I have a keen interest given my use of one of these 10hp diesels on Belaero. Looks like I can get another HP or 2, lower my bsfc and pollute a bit less with the use of a little turbo.

Anyone tinker in this area?

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Old 12-14-2010, 01:27 PM   #234 (permalink)
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Quote:
Originally Posted by NeilBlanchard View Post
...
That makes it seem like most of the FE for diesels is due to the higher energy level of diesel itself, and only a little is because the engines are more efficient.
boo! This thread is replete with the details of why this is not the case, you are not paying attention, I'm done typing.
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Old 12-14-2010, 04:29 PM   #235 (permalink)
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2009 VW TDI has 41MPG Combined EPA rating.

2009 Jetta TDI's Mediocre EPA Rating Not Whole Story

41MPG x 0.9 = 36.9MPGe

Where's the advantage of 42% vs 25% efficiency?
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Old 12-14-2010, 05:27 PM   #236 (permalink)
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Quote:
Originally Posted by NeilBlanchard View Post
2009 VW TDI has 41MPG Combined EPA rating.

2009 Jetta TDI's Mediocre EPA Rating Not Whole Story

41MPG x 0.9 = 36.9MPGe

Where's the advantage of 42% vs 25% efficiency?
The Jetta TDI is rated 30/42, the equivalent gasser is rated 23/30. There is your advantage.
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Old 12-14-2010, 10:30 PM   #237 (permalink)
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Point taken -- it's funny, but my 1987 Golf 1.8L got about 36MPG. And it lasted 14 years and ~217,000 miles; the engine ran wonderfully to the end. It died of rusty chassis...
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Old 12-14-2010, 10:37 PM   #238 (permalink)
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Neil, If you want to believe the EPA cycle on this one, you can and I wont. I have ridden in and driven TDI jetta's and knwo that this information is completely wrong. Steady state driving on the highway, on the flat, and city yields much better FE than the EPA shows. This is not accurate and my friend and I do not hypermile. But, as usual, whatever you want to believe, read, or not read, and use as your metric, go ahead.
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Old 12-15-2010, 12:55 AM   #239 (permalink)
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Quote:
Originally Posted by NeilBlanchard View Post
Point taken -- it's funny, but my 1987 Golf 1.8L got about 36MPG. And it lasted 14 years and ~217,000 miles; the engine ran wonderfully to the end. It died of rusty chassis...
Yes, and Honda CRX HFs routinely get 45-50 MPG and last at least a couple of hundred thousand miles. And Geo Metro XFIs tend to get even better MPG and last a decent while as well.

Note that none of them would pass current emissions or collision testing, nor do they have sixty-seven cup holders and lots of head, leg, shoulder room, automatic climate control, and on and on and on.

Apples and oranges, my friend.

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Old 12-15-2010, 11:58 AM   #240 (permalink)
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I get the EPA isn't the real world. So, using the adjusted numbers of the 2009 VW Jetta TDI manual vs the 2009 VW Jetta manual:

30 city / 41 hwy = 27MPGe / 36.9MPGe

21 city / 31 hwy

So the actual difference is about 16% on the highway (and nearly 33% in the City?!). That does jibe with the efficiency of the engines. So, in theory if the engine could manage to be 54% efficient instead of ~42% that the TDI or 25% of the gasoline engine -- then the highway mileage would be 40-41.3MPGe. Not too great, really.

Keep in mind, that the Volt is rated at 93MPGe in EV mode, 60MPGe combo mode, and 37MPG gas only. The Leaf is 99MPGe Combined. And the 2010 Prius is 50MPG Combined -- the plugin will be better.

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