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Study: Some car models consuming around 50% more fuel than official results

transportenvironment.org

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Re: Study: Some car models consuming around 50% more fuel than official results

#311

Post by brc »

lucaspiller wrote: post #172
kwelstr wrote: post #138

Earlier quoted context omitted.

And when in the highway don't go too fast, speed increases drag etc. etc.

I did some tests on a long drive last week, for the Smart Forfour I had this was the fuel consumption. It was all along flat, straight parts of the highway. Reports were based upon the cars own fuel efficiency monitor. - 135 km/h 7.8l/100km (30 mpg) - 125 km/h 6.5l/100km (36 mpg) - 115 km/h 5.4l/100km (43 mpg) I never realised speed made such a difference! (Mpg is US gallons)

A dramatic demonstration of this is the Bugatti Veyron. Between the original version (1,001 hp) and the SuperSport version (1,184 hp) - the top speed only increased from 408 kmh to 431 kmh. So a 183 hp increase in power yields only a 23 kmh increase in top speed - bearing in mind that 183 hp is more than most passenger vehicles have in total.

It gets exponentially harder to push air out of the way the higher the speed gets.

Re: Study: Some car models consuming around 50% more fuel than official results

#312

Post by oxryly1 »

JustSomeNobody wrote: post #162
Bud wrote: post #29

If you read the full report, the automaker with by far the largest gap between its claimed improvements in fuel economy and its actual on-the-road performance is General Motors. Much worse than VW and Mercedes (who also did very poorly), by this measure. A reckoning is coming. source: see page 13, here http://www.transportenvironment.org/sites/te/files/publicati...

Assuming wrongdoing: GM will get another pass because it is "too big to fail." This has to stop. Execs need to start going to prison.

Better yet, go after the shareholders.

Re: Study: Some car models consuming around 50% more fuel than official results

#313

Post by TylerE »

brc wrote: post #305
nostrademons wrote: post #250

Earlier quoted context omitted.

The StackExchange post that he linked lists several cases where it's possible. I was skeptical too - I was a physics major in college, I know all about potential vs. kinetic energy and rolling resistance. But engines are not perfectly efficient: you're going to lose some energy to internal friction within the engine, and to combustion efficiency, and to transmission losses, and to a number of other effects which vary…

Engines are most efficient at WOT. Hilly ascents at WOT will burn the fuel more efficiently (even though you're using more). Add a descent in which the computer stops providing fuel and it's possible that you could get a better mileage. It's known that you can get better fuel economy by oscillating speed on flat ground - using WOT to gain speed, coasting back down, opening up WOT again. This is because the engine is…

Generally not wide open throttle - see the efficiency maps I linked to in another reply. Generally peak is at somewhere around 1/2 to 2/3rds maximum output.

Re: Study: Some car models consuming around 50% more fuel than official results

#314

Post by TylerE »

WalterBright wrote: post #309
aianus wrote: post #282

Earlier quoted context omitted.

I'm getting motion-sick just reading that :)

I've been known to do it when gas goes over $4 a gallon, but not when there are cars behind me.

Yep, and this is why moderate hills are better. It's essentially constant speed pulse-and-glide. Just building and releasing potential energy rather than kinetic.

Re: Study: Some car models consuming around 50% more fuel than official results

#315

Post by sokoloff »

TylerE wrote: post #313
brc wrote: post #305

Earlier quoted context omitted.

Engines are most efficient at WOT. Hilly ascents at WOT will burn the fuel more efficiently (even though you're using more). Add a descent in which the computer stops providing fuel and it's possible that you could get a better mileage. It's known that you can get better fuel economy by oscillating speed on flat ground - using WOT to gain speed, coasting back down, opening up WOT again. This is because the engine is…

Generally not wide open throttle - see the efficiency maps I linked to in another reply. Generally peak is at somewhere around 1/2 to 2/3rds maximum output.

Wide open throttle and percentage of maximum output are two different concepts. An engine operating at partial throttle has higher pumping losses (pulling air past the partially closed throttle plates).

An engine operating at WOT but still producing a fraction of its maximum output is certainly possible (and generally more efficient than an engine producing the same output at a partial throttle setting). A diesel engine is almost always in this configuration (metering fuel but generally not restricting air with a throttle plate) and a gas engine at low RPM but WOT is also in this state.

If tuned for efficiency in that config, it can be very efficient and is how many piston airplane engines are regularly operated where fuel consumption is an important part of range (and operating economics).

Re: Study: Some car models consuming around 50% more fuel than official results

#316

Post by rnovak »

joe_the_user wrote: post #306
rnovak wrote: post #270

Earlier quoted context omitted.

I'm not sure what your definition of alter is, but for me to alter means to lie . They weren't simply optimizing for test conditions, they were outright lying during test conditions. that's what the EPA is saying is against the law. Here's the thing, and this is my main point: If the EPAs test conditions reflected normal driving habits, there would be zero difference between Manufacturer reported numbers and real wor…

IDK if you've ever been through an emissions test (like the ones GM actually goes through), but they're a complete joke as to simulating real world behavior. Does not matter. Your argument is something like, that by dumb luck auto manufacturers produced good emissions results and terrible results in the field. As understand it, the EPA is saying that if a manufacture is engaged in your two stage approach, "Optimize f…

No. That's not my argument. It has absolutely nothing to do with dumb luck.

The EPA has a set of standards, and manufacturers optimize for those. That's it.

Cheating != optimization. Cheating is like a kid copying someone else's answers. Optimization is studying before the test. Completely different things. And optimization isn't illegal.

If you still don't get it, I don't know what to say, I can't explain it any further.

Re: Study: Some car models consuming around 50% more fuel than official results

#317

Post by rnovak »

semi-extrinsic wrote: post #304
rnovak wrote: post #301

Earlier quoted context omitted.

I'm not sure what that proves, at least relative to what I'm saying? IFF the EPA's regulatory test procedure accurately described/expressed normal driving habits, then the only way that numbers would differ between the real world and the reported numbers would be fraud / lying / alteration , like what Volkswagen Group engaged in (let there be no mistake, it WAS fraud/lying, not a case of poor optimization). BUT the E…

So the point is that these official numbers should be taken with a generous pinch of salt. Now, when you talk about GM, remember this is data from Germany, so GM essentially means Opel. Now I believe that before the quite successfull Insignia which launched in 2008, Opel were mainly known for cheap and efficient and small cars like the Corsa and Astra, while now they have a more premium lineup, and "Turbo" versions o…

Yes exactly, with a pinch of salt. Exactly what I was trying to say.

And yeah, I've driven a Chevy Spark, and that thing was so slow I could get out and walk faster. I could totally see people driving with their foot to the floor in it.

Re: Study: Some car models consuming around 50% more fuel than official results

#318

Post by nkurz »

Theodores wrote: post #300
nkurz wrote: post #273

Earlier quoted context omitted.

Consider a different visualization: what if instead of a hill, you were crossing a valley? Starting at the top of the hill, you coast down and make it most of the way up the other side. Are you certain this will take more energy than pedaling the whole way across the flat? What if you can start by coasting 90% of the distance with zero expenditure of energy? What if it was 95%? Now assume that your chain is extremely…

Even a rusty chain is ridiculously efficient - in the high 90%'s. An ICE and drive chain is pitiful in comparison, so let's substitute the chain for a missing rear axle nut so that, when pedalling, the wheel pulls to one side and creates tangible frictional losses. I grew up in a very hilly area plus I have done a few continental rides where hills can be graded nicely and go on for 10 - 20 miles with little change of…

Did you read the linked stackoverflow discussion? I thought it made a convincing case that greater efficiency was possible across a valley given a sufficiently-aerodynamic low-rolling-resistance vehicle with an engine of non-constant efficiency. Would your intuition also say that analysis is wrong? Is it?

Re: Study: Some car models consuming around 50% more fuel than official results

#319

Post by Theodores »

TylerE wrote: post #307
Theodores wrote: post #300

Earlier quoted context omitted.

Even a rusty chain is ridiculously efficient - in the high 90%'s. An ICE and drive chain is pitiful in comparison, so let's substitute the chain for a missing rear axle nut so that, when pedalling, the wheel pulls to one side and creates tangible frictional losses. I grew up in a very hilly area plus I have done a few continental rides where hills can be graded nicely and go on for 10 - 20 miles with little change of…

> If it was quicker/more efficient to go up and down hills we wouldn't have land speed records be they by bicycle or rocket car set on dead-flat courses, would we? That's a total non-sequitur. Land speed record attempts happen in flat places to keep them from turning into AIR speed record attempts.

Nope. If your vehicle goes over a hump back bridge then maybe, but not if you go down one side of a valley and up the other side, obviously with an inverted wing shaped profile to the vehicle?

Re: Study: Some car models consuming around 50% more fuel than official results

#320

Post by eveningcoffee »

eveningcoffee wrote: post #292
MagnumOpus wrote: post #241

Earlier quoted context omitted.

What are you on about? For any given type of fuel, fuel consumption is related exactly 1:1 proportionately to CO2 emission (as carbon particulate and CO emissions are microscopically small these days). That is basic chemistry - where else would the fuel go? Therefore any claim about CO2 emissions equates to a claim about fuel consumption.

Yes, it should be. The problem is that these findings do not reflect my anecdotal experience. I have two recent measurements. About 500 km round trip and small trips inside the city. This is accordingly about 17% and 21% increase (and it was in the same region for the older model of the same car). Sorry, I did not include the make and model of the car because I do not want to leak too much personal information but it…

After carefully reading again what they stating stating, it appears that even when they talk about CO2 emissions, they actually base their claims on self reported fuel consumption data from http://www.spritmonitor.de

It looks to me that the following is entered (I have not used the app) by the users.

Objective data:

  Date of fuelling,
  Current odometer value,
  Amount and price of fuel.
  Type of tires (summer/winter) [should be mostly objective]
Subjective data:

  Driving style used (Moderate, Normal, Fast),
  Roads driven (Motor-way, City, Country roads)
For roads driven all the options could be selected and are then doubly reported in the detailed statistics.

This means that there is no objective acceleration and speed profile and also elevation difference data is missing (is not collected).

To illustrate this I will compare two different entries for BMW 3er 320d touring efficient dynamic

1) http://www.spritmonitor.de/en/detail/595885.html?cdetail=1 (2012, 120 kW, 4,14 l/100km) 2) http://www.spritmonitor.de/en/detail/672858.html?cdetail=1 (2011, 120 kW, 5,54 l/100km)

As both cars have the same power, I assume that they are the same model.

The consumption difference is 33%!

Driver one believes that driving style has been mostly moderate and driver two believes that driving style has mostly been normal.

Edit: I think that it illustrates that it is possible to drive this car close to its spec but it also easy to have more courageous driving style.

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