Wow. 2015 VW Golf TDI gets 50 MPG at 75 MPH!

And then there's the issue of regen cycles to burn exhaust particulates. Really need to drive much longer to get a more accurate fuel economy number.

 

A 150-mile Leaf for $25,000......hummmmmmmm!

 

A 477 mile trip probably included a regen, unless the 2015 is significantly different.

 

I was hoping you might post:

Do you have any more technical data or reports on what VW did to the engine. The body sounds interesting too. Perhaps an SAE paper or something more technical than the traditional, automag reports?

I've long suspected the injector pumps of being an energy hog so I was wondering if they might have gone electric pressure pump.

Thanks,
Bob Wilson

 

Bob,

There were fairly detailed technical data on the EA288 TDI posted on Green Car Congress a few months ago...

Green Car Congress: A closer look at the basics of Volkswagen Group’s important new 2.0L diesel MDB engine

 

True for power output big loss, but a bit less significant to BSFC values.
www.dtic.mil/dtic/tr/fulltext/u2/a576150.pdf

 

This is inaccurate:

• TDI (Turbo Diesel) - the turbo charger keeps the engine inlet pressure much lower. Furthermore, the injected fuel burns 'lean'.
• Otto - because of the reduced air pressure, the engine throttle is opened wider at partial power, reducing pumping losses.

It is only the peak power that is impacted by lower air density.

Fortunately the ratio of oxygen in the air is near constant so an Otto engine can operate with the throttle plate open wider, avoiding pumping losses from partial throttle operation. It has little effect on a diesel since they run best with the throttle wide open. The turbo supercharger lets the diesel run at a lower, effective altitude.

Power is not the same as engine efficiency. Efficiency is the amount of fuel burned per HP or the BSFC that counts:

• 20 hp @sea level ~= 1.5 gal/hr.
• 20 hp @6,000 ft ~= 1.5 gal/hr. (a gas engine has to lean the mixture to keep running)

The greatly reduced aerodynamic drag on the vehicle means the engine power required at any given speed is significantly reduced. So private pilots on long distance trips fly at the highest possible altitude assuming there are no head winds to fight at altitude. We do that for maximum range, the furtherest distance traveled for the least amount of fuel.

Acceleration is unimportant compared to the steady-state fuel burn per mile. Higher altitudes and temperatures (the term is density altitude) determines the ultimate vehicle efficiency. Vehicle efficiency is more than just the engine but also includes the drag energy needed.

Bob Wilson

 

Fuel Prices Here (Yesterday Afternoon)
E10 Regular: $3.25
Diesel: $3.70

I concede that without DEF, which is probably more of a PITA factor than a significant expense, the fuel price deltas are closer to 10-15-percent than what I quoted.
I'll also add that even if Vee Dubbayas were 10-percent cheaper to buy and fuel than Priuses, I'd give the house the 10-percent against the possibility of a major four-figure repair bill tilting things back in favor of Das Auto.

 

Diesel is about 40 cents more a gallon here, maybe 35 cents at some stations.
DEF is cheap. About a half cent per mile, conservatively, with paying $4.80 a gallon for the big jugs from Wal-mart or auto parts store. Truck stops charge around $2.50/gal for it from a pump. Of course, letting Mercedes dealer do it for you will make it pricy.
Since the DEF filling will likely occur with an oil change, keeping the washer fluid topped off during the winter is more of a PITA.

Fortunetly, we are no longer limited to VW for a diesel. Granted, some may not consider GM, BMW, or Chrysler much better. Hopefully, we'll get more choices, and more people will more from an inefficient vehicle to something better.

 

That's an excellent point.

 

Official EPA rating for the 2014 model with 2.0 engine was 42 highway. Color me unimpressed. The highest rated cars are 45 Mirage gasoline and 46 BMW diesel.

 

True on the latter, but absolute baloney on the former. I may have to downshift more when climbing over Vail Pass, but ALL my cars over the past quarter century produce(d) significantly better MPG at higher elevation than down at sea level.

 

Honestly, I would not drive a POS diesel that burns fuel at idle in the city. I like a car that shuts the ICE off when I lift my foot off of the accelerator pedal. I guess this car would be great for someone that lives right next to the Freeway/Highway and works right off the freeway and... has no requirement to drive in the city and has tons of money to burn on the higher cost of diesel. I don't fall into any of those categories and I'm betting most do not either.

 

That only seems partially right. On a turbocharged ice (diesel or spark ignited) altitude and temperature don't effect efficiency much.

On an otto ice, unless it was severely over sized there will be aditional losses. I know taking off from lake tahoe on a warm day, I have burned a lot more fuel, some of it circling to clear the mountains on the way back to palo alto. If you don't need the ices power the drop in efficiency is less.

performance is only unimportant on flat roads, if there are hills a non turbo engine may need to spin faster giving higher frictional losses to have enough power. Let's face it flat roads are easy;-)

 

That sounds like an aviation engine, not an automotive engine. Did it have the closed loop emission controls required on modern Otto-cycle auto engines?

If not, then it is a different case than the modern car case that I would discuss. That closed loop emission control using the oxygen sensor is a necessary part of my argument about efficiency not declining with altitude. Uncontrolled open loop carburetor systems may well experience mixture changes that alter efficiency.

 

definitely an airpane, as indicated by circling ;-), but it was an otto engine.

Let's take something low like 2000 meters, 6600 feet, we get down to 0.8 atm. If said ice is 10:1 otto, then we will only get 80% of the air or charge. Its friday afternoon so I'm sure its a little different but that would have the efficiency of an 8:1 ice not 10:1. IIRC and please correct that is about 4% less efficient. Great if you were on 80% throttle, now it can be wide open, but not if you are on a full load. Where this will be felt is accelerating to speed, and for hill climbing.

On a plane the higher altitude means lower drag, so the power requirement straight and level drops faster than the efficiency hit, as bob stated (just a little differently). Pilot can lean the mixture to be fairly optimal. In a car we have friction with the road, that gets in the way. The big hit on a hot day in lake tahoe, is that you need to go farther on a low powered plane to climb. A cold day, has more dense air, and better performance.

I have no idea if in a prius the efficiency hit of 0.8 atm would drop the compression stroke from 9:1 to 7.2:1, IIRC the variable valve timing goes from 9:1 to 6:1. Its not that much of a hit. You would feel it more in higher rpm to get to the same power level. Once you get up to speed, lower drag reduces the power level (fuel consumption) needed to maintain speed on a level road.

 

Could the engines have been advancing the timing. The less dense air at altitude means a lower effective compression ratio. Which is why a lower octane rating than regular is possible to use in higher places.

 

Why would it have to adjust anything, beyond opening the throttle plate a bit more?

Austingreen's airplane may spend considerable time at WOT, during every takeoff and climbout, so peak cylinder compression pressure matters a lot.

But my cars (before Prius, at least) spend very little time anywhere near WOT. My takeoffs and 'climbouts' out of the Tahoe basin are done less aggressively, with more restricted throttle positions. Under most higher altitude conditions, I can just open up the throttle somewhat more, and get the same intake manifold and combustion chamber pressures as at sea level. Only on the steepest mountain pass climbs where I really use WOT will the missing sea level capability be apparent, forcing earlier downshifts.

But away from WOT, the efficiency gain from reduced 'pumping loss' (in non-hybrids) is quite real at higher elevations.

Pilots can also adjust the fuel for leaner or richer mixtures. Drivers in modern emission-controlled cars don't have this choice, the computers mostly stick to a fixed mixture ratio.