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

#331

Post by eveningcoffee » Thu, Oct 01, 2015, 1:14 PM UTC

marze wrote: post #324

eveningcoffee wrote: post #264

Earlier quoted context omitted.

If you assume perfect burning then all carbon burned will turn into CO2. Therefore more CO2 may actually mean more efficient burning and smaller fuel usage (for the same amount of power i.e. less CO, less other particulate matter). This could happen for example when the engine could not take enough air to burn efficiently (for example because it is stationary). Unless we have also fuel consumption we could not know w…

Uh, so you think an appreciable amount of carbon is going out another way? Like carbon monoxide? Or unburned hydrocarbons? Neither compares to CO2, as a fraction. You are simply wrong. CO2 emission is proportional fuel consumed.

Yes, I understand.

The problem is that the report authors do not explain their methodology and interchange freely fuel consumption and CO2 emissions without clear explanation (did they measure CO2 emissions directly? did they calculate it from fuel consumption?).

This is not proper reporting in my mind.

Beside they base their reporting on self reported (i.e. not automatically measured) data from http://www.spritmonitor.de/ that does not provide any objective information about the driving cycle.

See for example these two 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)

It is about 34% difference. Why? No idea.

Well, maybe the first driver drove very carefully. Maybe the other car is broken or the driver likes to accelerate a lot or is driving on the hilly terrain.

It is also not known how many kilometers were driven on the city roads or highway as they are hard to separate in the data.

We also do not know which driving mode (eco, normal, sport etc) was used as it is not reported.

Car makers report different fuel consumption or CO2 profiles. Against which was comparison completed?

I think that this is sensationalist reporting with an agenda that is not well executed.

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

#332

Post by rebootthesystem » Thu, Oct 01, 2015, 5:27 PM UTC

mikeash wrote: post #260

rebootthesystem wrote: post #258

Earlier quoted context omitted.

I think you missed my point: real world driving. No vehicle meets manufacturer specifications in this regard, electric or IC. To be clear, I am not saying this as a negative. I am simply stating it as a fact.

You missed my point, which is that it's easy to achieve rated range in a Tesla with real-world driving. I have not taken care at all to drive my Model S in an efficient manner, and I still have an average of 315Wh/mile over about 8,000 miles of driving so far, where 300Wh/mile is rated efficiency.

The bit if data you are leaving out is the nature of the terrain and traffic you experience. I am not disputing your numbers at all, I am simply saying more data is needed in order to fully evaluate it.

Beyond that, the truth is you cannot get the rated range because that would mean draining the batteries to zero. Real range anxiety, depending on where you drive, starts to come in somewhere below 50 miles from fully drained.

You also have a difference in performance between summer and winter driving. If you have a short daily commute, the combination of the "off" state drain on the battery overnight and the car warming or cooling the battery pack while parked in cold or hot weather can have an impact on available range and performance.

BTW, I am NOT saying any of this is bad. I am simply saying these are realities of the contrast between advertised specifications and performance under real life conditions.

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

#333

Post by mikeash » Thu, Oct 01, 2015, 7:10 PM UTC

rebootthesystem wrote: post #332

mikeash wrote: post #260

Earlier quoted context omitted.

You missed my point, which is that it's easy to achieve rated range in a Tesla with real-world driving. I have not taken care at all to drive my Model S in an efficient manner, and I still have an average of 315Wh/mile over about 8,000 miles of driving so far, where 300Wh/mile is rated efficiency.

The bit if data you are leaving out is the nature of the terrain and traffic you experience. I am not disputing your numbers at all, I am simply saying more data is needed in order to fully evaluate it. Beyond that, the truth is you cannot get the rated range because that would mean draining the batteries to zero. Real range anxiety, depending on where you drive, starts to come in somewhere below 50 miles from fully…

That's fair. I think we can say there are two kinds of "do you achieve these numbers in the real world?" One being whether you can do so without completely artificial conditions, and one being whether you always get the given numbers. It seems we're just talking about different ones there.

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

#334

Post by bonzini » Thu, Oct 01, 2015, 8:54 PM UTC

TylerE wrote: post #191

userbinator wrote: post #166

Earlier quoted context omitted.

Are you in an area with much hilly terrain? That'll definitely increase fuel consumption significantly.

Actually, it depends. Modern cars do better in rolling hills than on perfectly flat land, since they can cut fuel entirely on the downhill, and the climbs don't require that much extra fuel over just maintaining speed. Now, mountains are another story, of course. Some good stuff in this SE question: http://physics.stackexchange.com/questions/6220/can-a-car-ge...

My anecdotal data is that my personal best (30 miles with less than a gallon) was indeed on such a hilly drive.

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

#335

Post by btilly » Fri, Oct 02, 2015, 1:28 AM UTC

mikeash wrote: post #303

jtuente wrote: post #278

Earlier quoted context omitted.

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.

Right. And if you're measuring miles per gallon, you're interested in energy consumed per mile traveled, not energy consumed per second. And aerodynamic drag tells you energy consumed per mile traveled thanks to the relationship that energy is force times distance.

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

#336

Post by codfrantic » Fri, Oct 02, 2015, 2:00 PM UTC

trymas wrote: post #57

[deleted] wrote: post #34

Earlier quoted context omitted.

[deleted]

I agree that cars are very heavy now, though, usually there are few 'types' of car weight. I do not know which where is used. Usually there are 2 weights: unladen weight and maximum weight. I've heard about some third weight which is between the unladen and maximum weights, something like a car's weight with full tank and a driver, but don't quote me on this. Probably you have the maximum weight listed. My Skoda Fabi…

He's probably talking about a hybrid e-Up. which is around 1200 kg because of the battery and electric motor tech, The normal Up Weighs around 850 kg.