[jobinjv]

Originally Posted by akroy

Density = Mass / Vol
What you pay is for the Vol (in litres)...When the density is high you get more mass of the chemical components in a lit of volume which otherwise is lesser during hotter temperature...
More molecules per lit means more combustion for a lit of fuel and hence more FE...

Hope that clears your point....

Abhi

dude got you on that point but as how can there be an increase in the volume like absar said when you fill at cooler times.. its just better fuel right.. hope what i am trying to say is clear..

[akroy]

Yes Yes, there is no change in volume but more fuel molecules in the same volume in the mornings than in the afternoons.....hence the change in density
in this case only the mass changes per unit volume...volume doesn't...hence u get better quality fuel per unit volume in the monings....

Abhi

[SirAlec]

@ srishiva...
dunno dude but....if i remember my highschool physics well... temp and pressure has very little effect over density of liquid and solids.....its the gas that is affected more....

hence pointless...!

[jobinjv]

Originally Posted by SirAlec

@ srishiva...
dunno dude but....if i remember my highschool physics well... temp and pressure has very little effect over density of liquid and solids.....its the gas that is affected more....

hence pointless...!

I am no Einstein either but this falls into the Gasoline category. Now, the reason why it is said so is because gasoline is denser in cooler state. There is no such change in the shape but the molecules bond more, whereas in conditions where the tempearture is higher like in the afternoon time there will be more vapours though the volume remains the same.

I suppose that is the way it goes..

[vasudeva]

The advice posted is absolutely the correct advice. We cannot change the traffic but we can definitely change our driving styles. I have seen personally that with a light foot, shifting up and down between 1000-2000 rpm, and never exceeding 2500 kmph, we cane increase our FE by at least 15-20% for the same traffic conditions. Regarding this advice,

The Optimum speed: Aerodynamic resistance increases exponentially with speed. For e.g. at speeds over a 100 km/h, your car will consume a lot more fuel than at 80 – 90 km/h. Keep within this limit to maximize the FE of your car.

This is correct. Both US Department of Energy EPA site and OECD show a speed and FE curve which show maximum FE at 50-90 kmph, and lower FEs outside this range. In a petrol car, 90 kmph corresponds to roughly 2000-2200 rpm. In fact EPA recommends not to exceed 60 mph (96 kmph) for best FE.

Other measures could include changing oil and air filters perhaps more often (after all this do not cost much, and can be done by anybody) and make a significant improvement to performance.

My conclusion: what is beautiful for yor legs and car is also the most FE (light foot, light engine revving, and light head).

[DerAlte]

Originally Posted by srishiva

Regarding the question about density and volume, wasn't there a article a year ago wherein it was mentioned that petrol stations made crores of rupees by not adjusting the volume to temperature ?

Since the fuel is stored on an average 2 meters below the surface, the temperature is relatively constant and is not likely to affect the volume of fuel delivered from the nozzle. We lose more money by other sharp practices done by the petrol stations; e.g. it is possible to trickle out about 0.5-1 litre of fuel from the filling pipe without the meter reading the trickle - the next guy in loses that much petrol but pays for the meter reading, which assumes fuel was full till the filling nozzle. Better to go to a station where they know you and wouldn't try tricks, or wait in a queue, rather than going to a station where there is no one.

What stumped absar was a common phenomenon called 'gas lock'. The pump attendant musn't have inserted the filler far enough into the filling inlet: the fuel going in must have foamed in the filling pipe leading to the car's gas tank. This must have resulted in fuel rushing back out and causing the spill. Foaming does not cause enough back pressure to trigger the fuel to stop. Try filling a narrow neck bottle from a tap full on and you will realize what happens!

The reduction in density with increase in temperature is more apparent in gas / vapour and less apparent in liquids (water is at it's densest at 4 DegC!). That is the reason for using Intercooler between a turbocharger and intake manifold - turbo compresses air increasing it's temperature and reducing the density of air (and oxygen); the intercooler reduces the temperature of the pressurized air to get more air (and oxygen) into the intake manifold. More oxygen = better burning = better power and burning efficiency = better FE (fuel as well as forex efficiency: we import fuel! ).

For naturally aspirated engines, the difference is easily noticeable between winter and summer in North India.

[partypest]

got some advise from some freinds i.e. while driving at high speeds you could change the gear to neutral and since you are at high speed the momentum keeps taking you forward untill you start slowing down... is that really good , will it help to improve mileage?

[DerAlte]

Originally Posted by vasudeva

The advice posted is absolutely the correct advice. We cannot change the traffic but we can definitely change our driving styles. I have seen personally that with a light foot, shifting up and down between 1000-2000 rpm, and never exceeding 2500 kmph, we cane increase our FE by at least 15-20% for the same traffic conditions.

That is Mach 3, vasudeva !!! Did you mean 40-60 Kmph?

I remeber a few ex-colleagues who used to take a turn at 40kmph on Rajdoot / Jawa / Yezdi - no matter what the road conditions were - because someone had told them that they would get best FE at 40-60kmph!!! (There was a particular gentleman who used to ride his new Yezdi in 1st gear all the time, because he was advised "1st year - 1st gear, 2nd year - 2nd gear" and so forth... but that's unrelated to this one)

[akroy]

Originally Posted by partypest

got some advise from some freinds i.e. while driving at high speeds you could change the gear to neutral and since you are at high speed the momentum keeps taking you forward untill you start slowing down... is that really good , will it help to improve mileage?

partypest, I dont think this is a good practice of bringing in neutral at higher speeds, Pls dont do it again....You will be saving fuel is absolutely a myth but u r definitely loosing out of your control of not engaging your engine control into braking or slowing down....Your engine should control your car and not your brakes...

Infact when u r in 5th gear doing higher speeds(say 100kmph) and remove ur foot of the accelerator, ur fuel is cutoff automatically (in MPFI engines) and engine braking mechanism makes sure that you are not out of control...U will achieve some unbelievable FE by the following practice...

say at 100kmph/5th gear u remove ur foot, let engine braking decrease the speed to 70-80kmph then u again put foot on the pedal and increase the speed to 100kmph and remove the foot again....and continue doing this process...

Abhi

[DerAlte]

Originally Posted by partypest

got some advise from some freinds i.e. while driving at high speeds you could change the gear to neutral and since you are at high speed the momentum keeps taking you forward untill you start slowing down... is that really good , will it help to improve mileage?

It will, but only if you are coasting downhill for 10 Km!

FE is not a constant figure - that is why the colloquial word is "average". More fuel is required - per meter of vehicle travel - to accelerate than to hold a constant speed. So the key is steady driving, as opposed to too much acceleration and deceleration - which, incidentally, is unavoidable except on highways, the Australian outback and places within the Arctic Circle.

Hybrid cars make use of this principle - by running the engine at constant RPM to maximize FE; power to the wheels is by electric motors (Toyota, GM etc.). Honda on the other hand uses electrical assist at the engine to channelize the energy of regerative braking into acceleration.

Going to neutral is definitely not a option - it definitely puts you in danger, since the only control you have on your car in neutral is braking and that may not be sufficient to avoid danger. It is easier to avoid trouble if the wheels have power.

[DCEite]

Originally Posted by partypest

got some advise from some freinds i.e. while driving at high speeds you could change the gear to neutral and since you are at high speed the momentum keeps taking you forward untill you start slowing down... is that really good , will it help to improve mileage?

There is a very long thread on this in the Technical section. The unanimous opinion was that shifting to neutral is not a good idea as you loose the option of engine braking.

[vasudeva]

I have seen personally that with a light foot, shifting up and down between 1000-2000 rpm, and never exceeding 2500 kmph, we cane increase our FE by at least 15-20% for the same traffic conditions.

Actually, this was 2500 rpm, which corresponds to around 100 kmph in petrol cars.

[DerAlte]

Originally Posted by vasudeva

I have seen personally that with a light foot, shifting up and down between 1000-2000 rpm, and never exceeding 2500 kmph, we cane increase our FE by at least 15-20% for the same traffic conditions.

Actually, this was 2500 rpm, which corresponds to around 100 kmph in petrol cars.

Yes, that makes a lot of sense.

Personally, I have seen the effect of on FE (and my own BP) by choosing a different time to commute: mistakes of others do not reflect on your driving style if you avoid collective frenzy of peak hour.

[prasanthalto]

Safety first..... FE second !!!

[partypest]

Agreed, thnx a ton guys, i will follow this practise for sure!!