Question about machine that runs on the road.

[Natstrackalpha]

sorry - could not resist, prob get nil replies and serves me right too . . .!

Being generally a nerd on fuel economy - I have an engine (which is attached to a car) and it is a diesel (I hate Diesels in aeroplanes as they tend to bancrupt operators . . .)

Back to the diesel engine then. I noticed that in the winter I get 10 miles to the quid or 125 miles on a tenner - and yet in the summer, the fuel consumption is considerably higher . . . ?

I checked for leaks and changed back to my old fuel supplier in case other fuels were less volatile. volotile, whatever, and yea, I am using more fuel in the summer.

How does that interest pprune . . ?

Just wondered if it could be air density helping the combustion along in the winter by being more dense but messing it up by being . . less dense in the winter?

(Moderators should be onto me within about five seconds, but at least it is technical - ( I bet it ends up in Jet Blast)

Edited edition = less dense in the (summer)

[RedhillPhil]

Temperature.
Engine draws in cold air in winter, cold air more dense, more dense more oxygen, more oxygen more efficient use of suck-squeeze-bang-blow. Principal of turbo-supercharging. Compressing (charging air) makes it warm, loses thermal efficiency so add intercooler to cool charge down.

The speed record breaking inter-war cars often had a compartment next to the air intake which before a run was attempted was filled with crushed ice in an attempt to cool the air down.



The answers all in air temperature.

[Cough]

I always find a diesel to be better in summer as there are less freezing agents in the fuel. Right up till the A/C goes on and the roads become congested!

Honest John has a this quote in a discussion on this theme...

Calorific values Winter diesel 36-38MJ per KG

Summer diesel 44-45 MJ per KG

[Genghis the Engineer]

Do you use the air conditioning most of the time in summer?

G

[pj67coll]

Depends also on wether or not there are winter or summer diesel blends where you are. When I drove a Mercedes diesel for several years the fuel consumption would be consistently higher in one season over the other. But that had a lot to do with additives in the diesel on account of emission controls.

- Peter.

[Michael Cushing]

RedhillPhil,

We have several anecdotal stories that absolutely contradict the "colder is better" story.

Cough described a 17% loss of fuel economy in winter. My gasoline vehicle gets 60 mpg in summer and 50 mpg in winter (that's miles and gallons, gentlemen) which is also 17%.

Is there some way to resolve these contradictions?

[UAVop]

Just wondered if it could be air density helping the combustion along in the winter but messing it up by being . . less dense in the winter?


Air is denser when cold. :sad:

Note that the denser air has the ability to hold more fuel that lighter air. This may appear counterintuative, but airflow to an engine is virtually constant (except when the engine is warming up on choke) Warming up the engine, simply aids combustion.
Given the average, there is only so much that can be managed, given the numerous single points that are common. ie, the computer will try to balance the OAT, intake velocity, intake volume with the fuel source. All fuel is not equal, so IF your vehicle has a fuel sensor, it can optimize that curve, if it does not, it will relegate the same average metering.
Average fuel metering, winter vs summer, creates a significant difference in economy.
As you know from aviation, there may be different additives, depending on weather, but also in general.
Diesel is especially notorious for a plethora of additives, meant to 'cut' the volume, the temp range, or just to get rid of PCB oil.

Do you get D1 or D2?
D1 is a thinner blend, and you wont get as good a mileage
Diesel can be cut with 5 to 10% biodiesel as well, this will actually increase capacity in diesel...
D2 with 10% bio is a monster of a blend! :ok:

[whiskey1]

Volume variation with temperature.
Hot fuel expands so lower mass, cold fuel contracts so more mass/per gallon.
It is the mass of the fuel that determines it's energy value.
Most (warm) countries sell fuel by volume uncorrected. Canada IIRC (for example) sells it's fuel corrected to Standard day conditions (cause it makes more money for the fuel companies).

[longer ron]

One should get slightly better fuel consumption in the summer...

Because in the summer you do not have a very cold engine,a cold engine has higher friction and it will take longer for the oil etc to get to normal temp during cold weather !

Another factor in the winter is that you may have your engine idling for 5 mins or so while you deice your windscreen :) this does affect your average mpg :)

In the winter my diesel was doing 52mpg (avg),it is now doing 54mpg(avg)...what does affect diesel mpg is short journeys!
On most modern diesels even the cruising speed does not affect the mpg dramatically,a high speed long distance motorway dash will not cost me any more than 2 mpg.

[longer ron]

BTW owing to the unusual hot weather recently...I have been using air con quite a bit ...dashboard still reads 54 mpg :)

[longer ron]

Oil viscosity graph :)

https://www.google.co.uk/url?sa=t&rct=j&q=&esrc=s&source=web&cd=8&cad=rja&ved=0CFEQFjAH&url=http%3A%2F%2Fwww.widman.biz%2FEnglish%2FCalculators%2FGr aph.html&ei=2-3kUcTHB6mw0AXlnYG4Bg&usg=AFQjCNFrwYKjYvs98xnFRgU6QfSgtHXj9A&sig2=c2q-tplssJgbL_RLOvwZYQ

[Denti]

In general under the same conditions in regards to driving style i do get a better fuel economy in summer. However, during the warm season i'm much more often inclined to drive with the roof down, considerably faster than 210km/h and using the aircondition. That really drives up fuel consumption. Winter tires (mandatory here by law) are usually limited to only 210km/h which limits the speed, not to mention unfavourable conditions like snow, ice and so on limit speed even more.

[Agaricus bisporus]

He he, but Denti, April first was some time ago...

[oxenos]

We all know that aerodynamic profile drag increases as the square of the speed.
Does anyone know what proportion of the power required to drive a car along is needed to overcome that drag, and what proportion is needed to overcome internal friction, tyre hysteresis, etc?

[Denti]

@AB have to say i do not really understand that comment. Was it about the speeds? We do not have a speed limit over here, driving faster than 200km/h is quite common if conditions (traffic, roadwork) allow it.

[E_S_P]

Dont forget most diesel engines are DI - direct injection so the only place where they 'mix' together with air is in the cylnder itself.

As RedPhil says, the colder the air, the more dense, so the mass drawn into the cylinders, is higher on cold days.

Hotter days less air mass = less power.
More throttle input to compensate= more fuel burnt.

[longer ron]

Yes you may get a little more power on a cold damp day,but for the reasons I posted previously and also as others have alluded to about winter fuel composition...any increase in engine efficiency is wiped out by the other factors previously mentioned.
I have driven diesels for 30 years and always get better mpg in the summer :)

[EEngr]

Yes you may get a little more power on a cold damp day,

You get as much power as you need to push the car along. The power vs air density curve may affect racing performance, where max power makes a difference. But not for day to day driving.

There are two things going on: Friction (engine and tire) vs temperature and engine efficiency vs temperature.

Air drag (like lift) goes down as temperature goes up. Engine friction is probably relatively constant once warmed up (being dependent on the thermostat set point). But engine pumping losses are lower for less dense air (warmer). And this probably affects diesels more so than petrol engines given their 'wide open throttle' operation.

The other factor is the additional energy needed to heat colder air up than warmer air. Thermodynamics isn't my specialty, but given displacement and RPM, the mass flow and resulting cylinder PV curves would reveal the work difference.
:8

[Michael Cushing]

EEngr may have the resolution. My 60/50 summer/winter experience comes from thirteen years of driving a hybrid that displays the instantaneous full consumption, as well as cumulative.

On a familiar piece of road, I can tell the headwind component just from looking at the instantaneous fuel consumption.

The resolution may be that the improved engine performance in winter is overwhelmed by the increasing drag. So far, I haven't had to worry about lift.

[longer ron]

In a diesel car the instantaneous mpg readout fluctuates wildly even with minute 'throttle' pedal movement - it is a useless measure for any practical purpose !!
I only ever use the avg readout.
Wind resistance/drag coefficient will vary between car models - mine is a fairly draggy shape which is why I lose 2 mpg on a long fast motorway run...in previous and more sleek cars - long distance motorway driving has actually given a better mpg.

[longer ron]

Anyway - no need to reinvent the wheel LOL
I took my own advice and googled it :)
This is a quote from a myriad of US websites that explain why winter 'gas mileage' is worse than summer...it is actually for a 'gasoline' vehicle but in this case there will be little difference between gas and diesel vehicles !!

1. More idling

This should be a no-brainer, yet parked idling cars are a common sight in cold weather. Resist the temptation to idle your car to warm it up. An idling engine gets 0 mpg. Consider also that idling the engine does nothing to warm up the tires and drivetrain.

Even in the coldest weather, you can begin driving after 30 seconds from a cold start - keep speeds low/moderate and use gentle acceleration until the temperature gauge starts to climb (source).

2. Low tire pressure

Of course you're smart enough to keep up your tire pressure as the temperature drops, right? A 10-degree (F) change in ambient temperature equates to a 1 psi change in tire pressure (source). Fuel economy declines 0.4 percent for every 1 psi drop (source).

3. Increased rolling resistance

Even if you're completely attentive to proper tire pressure, cold ambient temperatures will still cause your tires to return worse mileage. That's because a tire's shape isn't completely round - the sidewall bulges out at the bottom, and where the tread meets the road the small contact patch is actually flat. As the tire rotates, it constantly deforms to this shape, and this deformation requires more energy when the rubber is cold and hard. Rolling resistance at 0 degrees F is 20% greater than at 80 degrees (source 1, source 2).

4. Crappy road conditions

It's increased rolling resistance of another kind: driving through slush and snow. And then there's its wasteful polar (no pun intended) opposite: no friction at all! (A.K.A. wheelspin on ice.)

5. Lower average engine temperature

In the winter, an engine takes longer to reach operating temperature and cools off faster when shut off. Since the engine management system orders up a richer mixture when cold (proportionately more fuel in the air/fuel combination), more fuel is being burned overall.

A block heater can offset this problem (improving fuel economy by 10% in sub-zero conditions - source), as can garage parking, and combining trips (to minimize the number of cold/hot cycles).

Also related...

6. Higher average lubricant viscosity

Engine oil thickens as it cools. So does transmission and differential fluids and even bearing grease. Significantly more energy is needed to overcome the added drag these cold lubricants cause.

Using synthetic fluids can address this problem, since their viscosity changes less at extreme temperatures than traditional mineral fluids.

7. Weaker gasoline

Gasoline doesn't vaporize readily at very cold temperatures. So oil companies formulate fuel differently for cold-weather markets in the winter. Unfortunately, the changes that provide better cold vaporization characteristics also result in less available energy for combustion. You won't get as far on a liter of winter gas as you will on a liter of summer gas. (Source.)

8. Higher electrical loads

In colder temps, you use electrical accessories more often:

- lights (in higher lattitudes it's darker in the winter)
- rear window defroster (because it's easier than using the ice scraper, right?)
- heater blower motor (I don't have a/c, so this isn't balanced out during warm conditions); heated seats/mirrors
- windshield washer pump (because it's easier than using the ice scraper, right? And for frequently cleaning off dirty road spray.)

9. More aerodynamic drag

No, I'm not referring to the layer of snow you're too lazy to brush off the top of the car (though that would hurt mpg too).

A vehicle’s aerodynamic drag is proportional to air density, and the density increases as temperature drops. For every 10 degree F drop in temperature, aerodynamic drag increases by 2% (source).

[Natstrackalpha]

Air is denser when cold

sorry, I meant less dense in the SUMMER, not winter . . .:\

[Natstrackalpha]

Guys and guyesseses, thank you all for your inputs.

There is no aircon (are you kidding? Am still paying for training - "mummy, why are we starving?" -"Daddy`s training and nurturing his old diesel, honey . . ")

I think the tyres might have it - I`ll make `em like bricks next time.

Not having an air filter like an engineer`s oily rag might help too!

Thanks once again.

[oxenos]

Car MPG readouts need to be taken with a pinch of salt. Check fuel in against mileage driven over at least 1,000 miles, and compare.
On our last 2 cars, one was almost spot on, the other over read by 5.6%. Still checking on the latest car, looks to be about 4% overreading.

[DozyWannabe]

One thing that might be worth looking at is at the next service, get the garage to check the state of the particulate filter (or check it yourself if you're feeling handy). Cheap supermarket diesel may seem like a good cost-saving move in the short-term, but the amount of crud that ends up in the filter from using it consistently is truly shocking. The tip I was given was to fill up every 3rd tank with one of the detergent-heavy fuels (e.g. V-Power diesel in the UK) and take it for a high-speed motorway burn at the same time once a month or so. Of course, if a previous owner made a habit of only using the cheap stuff even that won't clear the crud, and the filter may need to be serviced or replaced.

Keeping the filter relatively clear will improve your fuel economy considerably no matter the season.

[longer ron]

Car MPG readouts need to be taken with a pinch of salt. Check fuel in against mileage driven over at least 1,000 miles, and compare.
On our last 2 cars, one was almost spot on, the other over read by 5.6%. Still checking on the latest car, looks to be about 4% overreading.

Which fortunately does not actually matter if you are merely comparing your own cars mpg figure between winter and summer,although I do always keep an eye on my actual fuel consumption fill to fill at the pumps ! :)

[Natstrackalpha]

wow, well, I washed the filters and pumped up the tyres and it feels like a formula 1 (only kidding about F1!)

I notcie fuel is less dense when warm so - in the summer maybe it is a better idea to fill up at the pumps with your . .tenner of fuel in the early morning, realising it may seem unfair, sending your wife out to re-fuel at 5 a.m, with the kids for company, but you would actually get more grams per litre.
S.G and all that.

Also- the tyres as you mentioned, as you said, buckle their form more on warm/hot roads and are squashier providing more resistance, result is pump them up to their highest service level/pressure/limit thang, preferably without blowing them up.

Air filter has to be clean or (even with a diesel) it would tend to run rich, providing less combustion or moreover same combustion, thats it, same combustion for more fuel - wow, who thought this could get interesting?

Again thanks to all.. By the way MPG readout:D, guys, I appreciate the . . compliment but my car is a cross between a wheelbarrow and a limo - on a scale of 1 to 10, 10 being a limo - it is definately a 1.

You are all talking A320 - am talking C150.:uhoh: - but one day . . . .

[Linktrained]

I used to drive the 100 miles home, pre dual carriageways or M-ways. It took three hours every time. Being much young(er) then, I tried to cover the same route as fast as I could... I "saved" just 15 minutes. I must have used more fuel, tyres, brakes and engine life. (Possibly frightening others, too.)

Thereafter I took three hours.

An aircraft economist factors in the cost of time as well as fuel etc. At its crudest a tramp or Hobo is not in the same urgent need of speed as the millionaire.

[longer ron]

Purely coincidentally I took a day trip over to Kimmeridge in dorset yesterday - so it was 120 miles each way of mixed Dual,Mway and country roads !
When we left sunny sussex the avg mpg was reading 54.2 and ambient temp approx 28deg.
After 100 miles of driving - with the ambient now reading 32 deg and having used the aircon continuously - the mpg reading had plummeted to 53.2 :).
Cruising where poss at 75 and using cruise control (not exactly subtle on the throttle ;) ) as req !

car = S hitroen C3 picasso 1.6 HDI - not exactly aerodynamic LOL

[Natstrackalpha]

I found the cause of the increse in fuel consumption.
There is a rubber pipe leading from the injector - I assume it is a scavanger or overflow pipe from the injector to the . . . fuel tank . . ?

Anyway, it was split - so I pulled it off, rooted out the bit still stuck in there, or rather the residual tubing and stuffed the tube back on again.

There was also a microscopic leak on the base of the No.1 injector, which I reckon will cause not much except at most = a tiny loss on compression, but I have not noticed anything, I`ll get a washer for that.

Since this hi tech 2 foot long limo cost me £100, I should really look after it.

Result - no fuel deposits on the base of the oil sump any more.

I wonder how many people fork out for a brand new car and all those monthly payments under the heading of: `the car is *****d we gotta buy a new one`

I love being obsessed with fuel consumption its so rewarding!

and, Longer Iron - your behaviour is shameful, you lost an entire mile of motoring over a distance of 120 miles - such waste!! But, those are really good figures! You can get 60 mpg if you try.:D

[cockney steve]

and, Longer Iron - your behaviour is shameful, you lost an entire mile of motoring over a distance of 120 miles - such waste!!

Balderdash and hogwash based on a totally false premise!
Currently I'm running a Volvo V40 T5 (a 40-series estate, 2-litre turbo-petrol:eek: ) Since late-february, I have not reset the computer, therefore, the AVERAGE fuel consumption is ~25.6 mpg. however, the last tankful was 26.8 mpg. calculated by filling when the same "miles remaining" shows and getting a receipt with the exact amount of fuel added.

Clogging it is fun!an old man's car that can spin the front wheels and out-drag an awful lot in the "traffic-lights grand Prix"....but that performance comes at a proce of single-figure MPG's on the instantaneous readout.As quoted by a previous poster, the total the average is taken over is all important.
That 1 MPG is reflected across however many miles the vehicle has travelled since the last computer "zeroing"

another "banger" driver! the car's a' 97 with cruise, aircon, leccy windows and sunroof, leather, towbar, alloys.....came with over 6 month's test and a couple of weeks' tax, all for £200....when I'm done, it'll drive into the scrappy's for 150 and the wheels/tyres, Blaupunkt CDradio and headlamps will fetch over 100.

now that's cheap and comfy motoring!:p

[Natstrackalpha]

It was a joke about the -one mile - over 120 - but you knew that right?
His consumption is admirable in hid Citroen.

I had a Volvo in my mis-spent youth. Most comfortable car ever - a 244GL and you know what? They all do 25 miles to the gallon.

Sadly, Volve have never seemed to hack it when it comes to fuel consumption - THEY ARE THIRSTY!! Other than that I would buy one tomorrow. Maybe fuel is cheap in Sweden!

[fc101]

Golf 1.9TDi (Variant aka Estate), approx 9 years old

ave Summer 5.3 l /100 km , Winter 6.0/100

However in winter we have snow, ice, colder starts, longer time for engine to warm, winter tyres and a different blend of diesel (and probably differing driving patterns too) etc

[Natstrackalpha]

In thanks for your non aviation input here is a list of stuff you already know.

Warm Air is less dense than cold air.

Dry Air is more dense than moist air.(Weird but true - the reason being that the molocules of air cause a displacement and take up the place of the . . air molocules, a bit like having a giant aquarium with a heavy model boat floating on the top.
Now, from a pipe with holes in the bottom of the aquarium, pump air into the pipe to cover the surface with air bubble, ship sinks.
Same principle as above, except now we are using air in water instead of water in the air).

But that provides the question: "Why don`t the air molocules - in the air - also provide lift . . ? . . or make the air denser by their mere prescence?

I know, I know - " I must get a life"

[Natstrackalpha]

leccy windows

now that is just showing off now . . .:hmm:

[kenneth house]

Humid air has less oxygen per unit of volume (i.e. less dense) available for combustion, hence weaker mixture and lower engine power output. Air at sea level is denser than that at higher elevations or in the case of a/c, flight altitudes. That is the reason to require a pressurized cabin above 12,000 ft--there is insufficient oxygen in the less dense air to sustain rational mental function... p.s. Good catch on finding the leaking fuel line.

[longer ron]

Hi Nats
and, Longer Iron - your behaviour is shameful, you lost an entire mile of motoring over a distance of 120 miles - such waste!! But, those are really good figures! You can get 60 mpg if you try

Sadly this car will never do 60 mpg...it is a very early C3 picasso - the slightly later cars had the engine/fcu tweaked for better mpg but I think even they would struggle to get 60 just because of the shape LOL :)

I had a Volvo in my mis-spent youth. Most comfortable car ever - a 244GL and you know what? They all do 25 miles to the gallon.

When I had my own glider - my towcar was a volvo 264 - with the Peugeot 2.7 litre V6 and auto box...it was such a torquey engine that the gear shifts were ultra smooth....great towcar (22mpg LOL).
I replaced it with a 244 (28mpg summer/25mpg winter) and I loved the footwell kick open vent - great for hot summer days :)
My worst ever towcar was a ford escort 1.6 diesel...no power but 65mpg easy to achieve :)

I found the cause of the increse in fuel consumption.
There is a rubber pipe leading from the injector - I assume it is a scavanger or overflow pipe from the injector to the . . . fuel tank . . ?

Yes it will be the return pipe,quite a normal fault on older diesels...well done on your fix btw :)

[cockney steve]

Humid air has less oxygen per unit of volume (i.e. less dense)

Water is 30% oxygen, air is ~16% ,IIRC.....therefore damp air contains more oxygen per unit volume than dry air....pedant mode off.

If we're talking about available oxygen, that might be a bit different,- OTOH, water-injection has been used to boost engine power-output.

Forgot to mention....the remote central-locking on the Volvo Oh, and although the old B-type engines were thirsty, they have used Mitsubishi, Renault and Ford engines . A 1.7 Mitsu. Petrol will do 40+ mpg, the renault diesel around 50 mpg.......but they don't have the Q-car appeal of the "wolf in sheep's clothing.:}

[Natstrackalpha]

Golf 1.9TDi (Variant aka Estate), approx 9 years old


nice! some of the best engines ever made - the Italians were quick to discover and buy loads of GTDs - I bought one, 5 door hatch or saloon, I can`t really tell the difference (brand new, yessiree) it was a dream, 1.6 lots of smoke when you give it welly though - naughty me:rolleyes: but one just HAD to play with the turbo - lots of lag, so, you go to second gear, go real slow, then just place your foot to the floor and wait, slow move forward, slight accelleration, then loads of smoke and she took off like a GTI - I was on the motorway once minding my own business, doing 70 and was follwing the same pack of cars, for the last 20 miles at night, all was normal and quiet.

Just then, a large BMW 5 came slowly cruising by with the Registration ATP - so, naturally, thinking they were pilots, I gently pulled out into the outside (fast lane) crept up nice and easy, dropped to fourth and floored the mother - in a . . .deluge of diesel smoke I burned up to about 110 - suddenly the nice grey BMW was on my tail with a little blue light flashing in the window screen - unmarked car murrs, cost me best part of a £100 in fine! AND he was an Inspector, still, rather serious fun I guess.:)


but easy, easy 60 miles to the Imperial Gallon, combined - nice!

[Natstrackalpha]

water-injection has been used to boost engine power-output.


true, true, true, the Harrier had it and so did the . . F27 Fokker Friendship