Study: Some car models consuming around 50% more fuel than official results • Hacker News Board

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

#301

Post by rnovak » Wed, Sep 30, 2015, 10:10 PM UTC

semi-extrinsic wrote: post #294

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…

So I threw together a histogram [1] of car CO2 emissions as reported by manufacturers for 1200+ model/engine combos. It's not exactly uniformly distributed, to say the least, there is a strong peak at 99 g/km etc. Now that's maybe not conclusive evidence that they are lying, but it's certainly suspicious. [1] http://asmunder.github.io/2015/09/A-histogram-of-CO2-emissio...

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 EPA's regulatory test DOES NOT accurately depict normal driving conditions.

In the current case, a manufacturer has to:

     - Realize and Formally accept that the test procedure is inaccurate
     - Optimize for:
         - Simulated driving conditions, aka the Test Procedure
         - Real life driving

To me, it looks like GM just didn't do any of that, and only optimized for the simulated conditions and not real world road conditions.

Depending how far out of wack the test procedure really is could explain the entire data-set.

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

#302

Post by mikeash » Wed, Sep 30, 2015, 10:13 PM UTC

enraged_camel wrote: post #193

ticktocktick wrote: post #103

Earlier quoted context omitted.

Just stay off the brakes as much as possible. No big secret really.

Unless your car has regenerative breaks, in which case you should randomly and unpredictably break to generate free energy. edit: downvoters are once again proving that HN doesn't get jokes.

As I always say, HN doesn't have a problem with humor, but it needs to actually be funny.

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

#303

Post by mikeash » Wed, Sep 30, 2015, 10:15 PM UTC

jtuente wrote: post #278

btilly wrote: post #190

Earlier quoted context omitted.

The reason why it matters is that air resistance is proportional to the square of your velocity. At high speeds that term dominates.

Due to some physics things that I don't understand, it actually ends up proportional to the cube of your velocity. source: presentation by Dr. Rizzoni at Center for Automotive Research at OSU

Power consumption is proportional to the cube.

Aerodynamic drag i.e. force opposite the direction of travel is proportional to the square of your velocity. Power consumption for steady cruising is equal to drag multiplied by speed. Thus power consumption is proportional to the cube of speed.

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

#304

Post by semi-extrinsic » Wed, Sep 30, 2015, 10:27 PM UTC

rnovak wrote: post #301

semi-extrinsic wrote: post #294

Earlier quoted context omitted.

So I threw together a histogram [1] of car CO2 emissions as reported by manufacturers for 1200+ model/engine combos. It's not exactly uniformly distributed, to say the least, there is a strong peak at 99 g/km etc. Now that's maybe not conclusive evidence that they are lying, but it's certainly suspicious. [1] http://asmunder.github.io/2015/09/A-histogram-of-CO2-emissio...

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 of several models.

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

#305

Post by brc » Wed, Sep 30, 2015, 10:48 PM UTC

nostrademons wrote: post #250

aianus wrote: post #210

Earlier quoted context omitted.

> Modern cars do better in rolling hills than on perfectly flat land, since they can cut fuel entirely on the downhill This is physically impossible. Even if the car was perfectly efficient at overcoming the force of gravity on the uphill portions (which it is not), you cannot do better than flat terrain (unless by hilly you mean 'net downhill').

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 most efficient under load and the average consumption works out better. Adding in the hills would average this effect.

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

#306

Post by joe_the_user » Wed, Sep 30, 2015, 10:49 PM UTC

rnovak wrote: post #270

joe_the_user wrote: post #261

Earlier quoted context omitted.

The whole controversy is over manufacturers reporting false numbers, i.e. lying. No, actually it isn't. The controversy is over manufacturers tuning their vehicles' engine behavior to give economy for the tests and for the tests only. By your criteria, that's not a problem but VW has already been bitten really hard by the revelation that they did this. ...You would have to prove that an improvement at throttle positi…

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 for:- Simulated driving conditions, aka the Test Procedure [and achieve high fuel economy] - Real life driving [and achieve high power, low fuel economy]" then they are engaging in systematic fraud and are going to get hit big time. You seem to think it's just a matter of technicalities in the test condition. I'd like references for that.

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

#307

Post by TylerE » Wed, Sep 30, 2015, 10:50 PM UTC

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…

> 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.

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

#308

Post by brc » Wed, Sep 30, 2015, 10:55 PM UTC

happyscrappy wrote: post #3

yc1010 wrote: post #2

"On average, two-thirds of the claimed gains in CO2 emissions and fuel consumption since 2008 have been delivered through manipulating tests" How deep does this rabbit hole go :( Here in Ireland the motortax for cars newer than 2008 is based on CO2 emissions, if motorists find their tax rising due to cheating by car manufacturers thats an unexpected and direct cost to their wallets.

Europe was really led astray when they were told that diesels were better for the environment, hybrids would have been the way to go.

Yes. Optimising for c02 reductions over Nox and particulates is a monumentally stupid policy.

Co2 may have a deleterious effect in 100 years time, but is not an issue for air quality today. In any case, passenger vehicle c02 emssions are a rounding error in the scheme of things.

Meanwhile, particulate pollution and Nox are very real issues affecting millions of people today. It's stupid to push diesel over gasoline for c02 reasons.

Part of the reason VW cheated was because the USA didn't fall into this trap and allow more lax emissions standards for Diesels - all fuels are held to the same standard. So they took the Euro engines and added the defeat code.

The USA is correct on this one.

The focus on passenger vehicles is idiotic though - the amount of Nox and particulates pumped out by a single container ship is immense compared to a fleet of passenger vehicles. Then add trucking, rail, stationery equipment etc...

Cities should be optimising for electric propulsion and punishing diesels. That makes sense for air quality right now, and if co2 proves to be an issue, it is easily fixed by switching the generation source to Nuclear or Hydro.

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

#309

Post by WalterBright » Wed, Sep 30, 2015, 11:01 PM UTC

aianus wrote: post #282

WalterBright wrote: post #269

Earlier quoted context omitted.

I read years ago that pulsing was the most efficient strategy. Engines have very different efficiencies at different rpms and power settings. The idea with pulsing is to try to operate it at its most efficient rpm and throttle setting, which of course rarely corresponds to the speed over flat ground you'd like to be travelling at. Hence pulsing.

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.

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

#310

Post by brc » Wed, Sep 30, 2015, 11:09 PM UTC

cannedbass wrote: post #112

So how many of these cars have turbos? I know the BMWs at least are mostly turbo 4-cylinders. The whole reason manufacturers are moving to small displacement turbocharged engines over large displacement naturally aspirated engines is because the EPA MPG tests never run the engine in a range where the turbo is doing much. Put the car in the real world and the driver's lead foot makes the turbo kick in, killing fuel ec…

Yes. Turbos are being added to everything, killing the NA engine. The reason is to create a smaller displacement motor which still has the power that drivers expect.

Turbo engines can consume vast amounts of fuel when opened up to full throttle. Modern turbo engines are also very easily remapped for extra power (and consumption) just by changing the boost control.

All the added complexity and cost just to match emissions requirements, which are all negated when the driver 'puts the boot in'.

Turbos are the ultimate cheat device.