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

Because these cars are computer control, and generally programed for the best blend of efficiency and power. Knock sensors allow the ECM to take the fuel to the edge of pre-detonation by advancing the spark timing, and to do so constantly. This improves both efficiency and power by letting the cylinder to get closer to top dead center before the flame front starts pushing down.

 

I don't see how that answers "why would it have to adjust anything?" at high altitude? Especially when I'm nearly always operating in the same manifold pressure range (i.e not WOT) as at lower elevation?

 

When I was doing my gasoline energy studies, I was using WOT up an 8% grade, 1.1 miles long, 525 ft (160 m) tall. I was able to observe the high octane fuel actually generated a little more power compared to equivalent energy content gas. However, this narrow operating range, WOT, did not make economic or operational sense for our Prius. Buying a high energy content gasoline did give a slightly a higher MPG but it was difficult to claim there was an economic benefit.

I was unable to find a high octane, high energy gas in the Huntsville retail market. The high energy gas retailers sold high octane gas but it had low energy content.

Bob Wilson

 

I suspect, because the prius uses relatively low compression (9:1) and often uses cooled egr, lowering the engine temperature, the ice is often in near optimal spark advance for efficiency, so not much can be gained by higher octane on our gen III engine on likely driving cycles other than a little better engine note on steep hills or high acceleration on hot days (yes it sounds better, I did the experiment, hot days for the electrical load of the a/c).

OK this note is mainly navel gazing, but for one thing noted the aggressive cooled egr of the gen III prius. In the prius the cooled egr allows more efficient operations at lower power levels (better efficiency at low rpm low load)and at higher power levels (runs cooler so rich mix and throttle advancement is not needed to avoid detonation) than the gen II before it (although peak efficiency should not be affected). The 2 liter vw diesel engine system did update the egr system to increase efficiency and reduce the amount of NOx before SCR after treatment. That should both increase its efficiency but also reduce the amount of urea consumed (fewer refills but they are cheap).

Both modern clean diesels and hybrids help reduce oil usage. A diesel is a good choice for a mainly highway going vehicle, but all of the current offerings do require more maintenance than toyota and ford hybrids. This may have more to do with the manufacturers than the technologies. In the city a diesel can operate more efficiently than a gas ice, but it can't come close to a hybrid. Its good that vw is going to produce both hybrids and plug-in hybrids for the us market, but diesels for most of the rest of the world. Hybrids don't sell very well outside Japan and the US, and I am glad vw and bmw are improving the technology for lower emissions and and more efficiency.

 

don't forget. you have to put "piss" in the other tank

 

Then how about, because it can.

First, does the car also measure the absolute atmospheric pressure to calibrate the manifold pressure reading? If not, the numbers at high altitude are off. Most pressure gauges are set to read the air pressure at sea level as zero. At 6000ft they will reading at -3psi instead of zero.

But we'll assume the manifold pressure is the same. To get the same pressure at altitude, the throttle plate has to be open wider. Now, with naturally aspirated engines, the air density going into the engine can never be greater than the ambient air density. A turbo or super charger is required to increase the density going in by compressing the air before entering the engine.

So regardless of the manifold vacuum pressure, the air will be less dense, and thus the engine's effective compression ratio will be lower. This reduces the chance of knock, which is why 85 octane gas is available in the mountains. When equipped with knock sensors, the ECM can advance the spark timing to the verge of knock again. This in part compensates for the lower effective compression ratio. Older cars didn't have as wide a range in which to adjust spark advance, and those without knock sensors wouldn't be able to adjust it automatically. So any gains for driving at high altitude would be less for them.

In other words, a modern, computer controlled engine has far more parameters it can adjust. So it can take a better advantage of the less dense air at higher altitude than ones of the past.

 

Which is really cheap, and less of a hassle than keeping the washer fluid tank filled.

 

I only have experience in the big trucks that have DEF systems. Urea is corrosive to painted or metal surfaces that you care about. I never had to pay for the stuff, but you add that cost on top of the premium price of diesel fuel.

 

So is road salt. DEF is around 30% urea. Cleaning up spills is a good idea, but it isn't a strong acid or base.

Above, I figured the cost of DEF would add a little less than a half cent per mile if a 10 gallon tank was totally filled every 10k miles using the 2.5 gal box available at a local store. This is the expensive estimate. These cars won't be using that much DEF. Many only have tank of around 7 gals. Then access to a truck stop will cut the DEF price in half.

The per gallon price of diesel gives most price shock. The per mile cost of the fuel ends up being around the same as the regular gasoline model. In practice it has a fair shot of being better.

 

It comes down to the right tool for the right job;

• towing, weight hog - diesel trucks, non-urban light diesel cars
• urban only - current EVs
• urban and intra-urban - hybrids in the Ford/Prius class, Honda Accord, plug-ins

We have choices with significantly improved price-performance options. So I welcome VWs new, modular body and engine architecture. If they can focus on ordinary gas car, conquest sales, good on them. The hybid/Prius customers are so few relative to the 20 times larger, ordinary gasser market, they might as well have burned that budget for all the good it did.

Bob Wilson

 

As best I can tell, the manifold absolute pressure reading (ScanGauge: MAP) is already an absolute pressure. No other calibration needed.

Engine off at 500 feet elevation right now, my Prius is showing a MAP of 14.6. I haven't watched this much, but seem to remember the previous non-hybrid operating mostly in the range of 3 to 10, less than the typical ambient air pressure at 6000 feet of about 12 psi. I don't floor it much.

Agreed here. Altitude should just set a WOT cap on MAP.

In modern cars, these sensors don't read vacuum pressure, they read absolute pressure. Temperature and absolute pressure in the intake manifold should be sufficient to determine intake air density, regardless of (and with no other indication of) physical altitude and conditions upstream of the throttle plate.

I'm thinking only in terms of absolute pressures in the cylinder, not that 'effective compression ratio' stuff.

Agreed here. I have heard about operating and efficiency changes in old fashioned carburated engines lacking the closed loop feedback of modern emission controls.

 

Diesel is "premium cost" in towns, but typically the same price as regular gasoline along interstates, and it gives you +10 mpg over the gasoline Beetle or Gulf or Jetta or Passat..... in other words you're saving overall.

Spark timing?
In a Diesel engine that using no spark plugs? (ponder) Well maybe you're onto something there.

 

Why do people think Diesel and Hybrid technologies are mutually-exclusive? Volkswagen has made several diesel cars that turned-off the engine when coasting or stopped..... including the Lupo 1.2 and Audi 1.2 that scored 90 US-mpg on the extraurban cycle.

 

VW discontinued Lupo because it was a car with far too many compromises and people were not buying it.

 

1) because of all the lies you told on here in the past, I don't believe what you're saying now.

2) because of all the lies you told in the past, I'm not going to research this because I don't care what you say.