worsening fuel economy

[TJW 44]

Hello there,

 

been wondering if I could ask if any of you had any thoughts/ideas on a problem that I have been noticing recently.

 

With myself exclusively commuting in London the fuel economy hasn't been anywhere near as some others describe it, but I was quite happy with the 60 mpg I've been getting. However, I've noticed a sudden drop in said fuel economy in October (after the annual service and MOT) and I'm now operating at 55 mpg. A few weeks ago I installed Oxford Heated grips but only had them on a couple of times … and I doubt it has something to do with them.

 

Thanks a lot ...

 

[ste7ios 469]

It's normal in the winter to have an increase in consumption. The more dense air needs more fuel, and the petrol recipe is different for the winter...

[Andy m 23,659]

Also more time on the enricher circuit/mode, more worry about keeping power down for grip and less thought for economy, more riding in the dark so more braking and less anticipation and yes even heated kit loading the alternator (a fraction of an MPG).

 

About the only thing we don't get is a change of fuel. I've heard of that sneaking in and causing a further drop.

 

I've plotted fuel use for years and you can tell time of year by the wave in the curve.

 

Andy

Edited November 30, 2016 by Andy m

[Tonyj 6,907]

tell you what the temp was low today so i recon i must owe esso if cold weather knocks the milage down . inner gloves lobster finger gloves heated grips base layers 2xneckwarmers , couldn't bleedin move :0)

i only get 60's in this weather around town

[dazznutts 167]

on my 750s my fuel consumption has pitched was getting around the 80 mark now dropped to 75

[Grumpy old man 4,682]

3 minutes ago, dazznutts said:

on my 750s my fuel consumption has pitched was getting around the 80 mark now dropped to 75

+1

[larryblag 14,236]

8 hours ago, Andy m said:

Also more time on the enricher circuit/mode, more worry about keeping power down for grip and less thought for economy, more riding in the dark so more braking and less anticipation and yes even heated kit loading the alternator (a fraction of an MPG).

 

About the only thing we don't get is a change of fuel. I've heard of that sneaking in and causing a further drop.

 

I've plotted fuel use for years and you can tell time of year by the wave in the curve.

 

Andy

I'll bet, if plotted out like Andy says there'll be a dip beginning mid October, a slight bulge in the curve at the opposite part of the calendar (Mar/Apr) and gradual climb from there till late September again?

Also, I'll bet the considerable current taken by heated grips will indeed make a difference. The alternator being driven directly  i.e. before the benefit of any gearing (apart from pully to pulley) will contribute a significant loading on what is a relatively small capacity engine when they're on?

Edited December 1, 2016 by larryblag

[MikeBike 5,007]

6 hours ago, larryblag said:

I'll bet, if plotted out like Andy says there'll be a dip beginning mid October, a slight bulge in the curve at the opposite part of the calendar (Mar/Apr) and gradual climb from there till late September again?

Also, I'll bet the considerable current taken by heated grips will indeed make a difference. The alternator being driven directly  i.e. before the benefit of any gearing (apart from pully to pulley) will contribute a significant loading on what is a relatively small capacity engine when they're on?

Your wish is my command... I wondered the same and have the data in Excel so made a graph.

A slight dip in Winter of about 5mpg I'd say, but there again my fill up in January last was more or less average. The two fill ups in Mar Apr 2015 were motorway and winds, the fill up in feb 16 was motorway no big winds, both about 63mpg, so nowhere near the OP's 55 but there again their original figure of 60 was low to start with in comparison to mine.

 

I have oxford heated grips and always use them in the colder months starting at 40% in Say Oct to max 75% in deepest winter.

 

Average over the whole period is 73.93mpg

Edited December 1, 2016 by MikeBike

[larryblag 14,236]

Impressive Mike! that's a lot of data nice one!

[TJW 44]

I've been plotting fuel data for about a year now and bizarrely enough I had 65 mpg pretty much throughout the last winter, then a drop down to 60 mpg and since mid-October a steady downward trend to a current low of 55 mpg.

 

 

[Andy m 23,659]

Average groups of three or five data points and you take the noise out caused by not-quite-fill-ups. Cut the plot range to just outside the normal distribution (roughly 55 to 85) and you may start to see trends.

 

Andy

[larryblag 14,236]

1 minute ago, Andy m said:

Average groups of three or five data points and you take the noise out caused by not-quite-fill-ups. Cut the plot range to just outside the normal distribution (roughly 55 to 85) and you may start to see trends.

 

Andy

 

And there we have it, statistics properly explained. Thank you Andy 

[MikeBike 5,007]

1 hour ago, Andy m said:

Average groups of three or five data points and you take the noise out caused by not-quite-fill-ups. Cut the plot range to just outside the normal distribution (roughly 55 to 85) and you may start to see trends.

 

Andy

 

Could you explain the 55 to 85. I'm puzzled why both on the +ve side of 50.

It's a long while since I did any statostics..

And can you tell me how you do that in Excel - maybe paste your formulas if you have yours in Excel

 

[Andy m 23,659]

I'm not in the office so may get the numbers wrong. You need 50 plus data points. Group them into 3's or 5's and work out the average and range of each group and the whole lot. Apply a formula where the control limits are the average of the lot plus and minus the range multiplied by a factor based on the sample size (you look this up). Your chart only nees to show enough to get the control limits (3 standard deviations).

 

So

 

 

Each point on the blue line is three fuel ups to take out noise. The solid red lines are where the plot should fall statistically if all is well. The step is where the Guzzi went and NC arrived.

 

Leave the basic data on the NC chart, plus me fine tuning the control limits as you come from an estimate to calculated and you get

 

 

The point off the chart should cause concern, but as I know this includes slow touring with my dad and a fill up from a can doesn't.

 

Are we bored yet?

 

Andy

[Andy m 23,659]

https://en.m.wikipedia.org/wiki/Statistical_process_control

 

Just in case anyone is still awake

 

Andy

[MikeBike 5,007]

I found I could let Excel take the strain and show a trendline through the actual points. (I selected a 6th degree polynomial.) The curve shows a clear seasonal difference of about 5mpg as I estimated before by eye on the raw data points. This trendline seems to do the required smoothing to factor out inconsistencies of individual fillups etc. I'm sure those who are statisticians could probably find details to fault my approach but it seems to do the job and the curve shows an interesting trend that is repeating almost exactly from last year to this.

 

[shiggsy 529]

16 hours ago, TJW said:

I've been plotting fuel data for about a year now and bizarrely enough I had 65 mpg pretty much throughout the last winter, then a drop down to 60 mpg and since mid-October a steady downward trend to a current low of 55 mpg.

 

 

I plot my fuel ups as well, Winter riding mpg drops by about 3-4 mpg (and I average 80).  Looks like you have something else going on there, that's a big % drop.

[embee 7,288]

Mike's plot above is exactly what I'd expect to see. Looks good data.

 

Just to comment on a couple of points.

 

Enrichment is only technically required for a very short time. Don't confuse enrichment with fast idle. When you first start a port injected (or carb) engine from cold, some fuel condenses out on cold surfaces so is not available for combustion. Petrol/air will only burn successfully within a fairly narrow A/F range. In order to ensure robust starting and avoid stalling, some extra fuel is required to compensate for that which condenses on the cold surfaces and the small amount absorbed into the oil film etc. Once the surface temperatures begin to warm, the condensed fuel starts to evaporate and the resultant mixture can in fact swing towards rich due to this extra fuel. Equilibrium will be reached quite quickly, maybe 30sec or so, and the base calibration takes this into account. After this point enrichment is no longer required. This is a plot I measured many years ago on my car, it shows the after-start enrichment ramps off after about 10sec, down to the base map.

 

 

For emission control reasons the closed loop control will be initiated as soon as possible, limited usually by the temperature of the lambda (EGO) sensor, and this would be expected to be no longer than 45sec or so (depends on the vehicle type and emission limits it must meet, hence the technology used). This time scale doesn't vary all that much with ambient temperature, and certainly within a minute or 2 it'll be under closed loop control. At this stage the A/F will be stoichiometric (14.7:1) give or take a very small variation. The sensor needs to be around 300c, 10 or 20degC change in ambient air temp isn't very significant. The plot above is for a car with old (c1992) technology and a fairly slow closed loop initiation, I suspect the glitches around 100sec are this effect.

 

After this stage the engine is still held at fast idle (extra air+fuel but not enrichment) purely for driveability and avoiding stalling, and the fast idle is ramped off as the temp increases, down to a normal idle speed. Fast idle of itself doesn't really contribute significantly to increased fuel consumption if you drive away reasonably soon after starting. The slow ramping down of injector pulse width on the above graph shows the reducing fast idle effect over the first 2 minutes at idle from a 10C cold start. It reflects more air+fuel for the faster idle speed, not enrichment.

 

The main factors in increased consumption with low temperatures are the increased heat loss during the cycle (thermodynamic loss), the increased frictional loss with cold oil, and the simple fact of having to heat 80+kg of power unit up to normal running temperature from a lower ambient. The number of cold starts versus distance travelled is always a very significant factor in real world fuel economy.

 

Cold air is indeed more dense, but the mass air/fuel ratio stays the same and the heat released is down to the mass of fuel burnt, the density of the air is of little consequence (that's essentially what you regulate with the throttle anyway).

Edited December 2, 2016 by embee

[MikeBike 5,007]

2 hours ago, embee said:

The main factors in increased consumption with low temperatures are the increased heat loss during the cycle (thermodynamic loss), the increased frictional loss with cold oil, and the simple fact of having to heat 80+kg of power unit up to normal running temperature from a lower ambient.

Save the planet - keep the bike in the lounge...

 

Presumably the air resistance of the bike is also higher as the air is more dense so the engine will have more work to do for the same speed.

Edited December 2, 2016 by MikeBike

[Andy m 23,659]

1 hour ago, MikeBike said:

Save the planet - keep the bike in the lounge...

 

Presumably the air resistance of the bike is also higher as the air is more dense so the engine will have more work to do for the same speed.

 

Yeah but no, white tarmac has lower rolling resistance than the black!

 

Andy

[Tez 72]

A lot said here, but has anyone one mentioned TYRE PRESSURES . Will affect fuel consumption quite a bit  

[kharli 100]

On ‎30‎/‎11‎/‎2016 at 21:47, Andy m said:

Also more time on the enricher circuit/mode, more worry about keeping power down for grip and less thought for economy, more riding in the dark so more braking and less anticipation and yes even heated kit loading the alternator (a fraction of an MPG).

 

About the only thing we don't get is a change of fuel. I've heard of that sneaking in and causing a further drop.

 

I've plotted fuel use for years and you can tell time of year by the wave in the curve.

 

Andy

Forgive me if I am wrong ,but as I understand it motorcycles use stators that run at full load and use the regulator to dump excess as heat ,so unlike car alternators you don't get extra magnetic drag when increasing load .

[bazza 3,629]

wow! Its amazing what a lot of highly tech members we have. logging consumption showing a 5mpg decrease in cold weather, truely humbles me . I just ride the bike and laugh at the fuel it uses compared to my can and van -both in the 30's per gallon.

The alternator question is interesting. In Morocco it's LAW that you can drive an night up to 20 mph without LIGHTS! OK if you hit a camel it won't help what speed you are doing on a bike but I always thought that was a crazy law.

is there ANY truth in the assumption that using a lot of electric power causes the engine to work harder - driving the belts? Its always been my assumption that using the air con uses more fuel - but my geeky mates is it a significant amount?

maybe we can have a graph showing what uses what it terms of power - lights, heated grips etc -forget the A/c as my bike hasnt got that yet! (must ask Fred to fit it!)

[chris 357]

Doesn't the NC alternator run at max output anyway with the regulator dumping excess? I doubt that you'd notice any impact from increased electrical load on the fuel consumption of the NC or pretty much any bike.

Edited December 5, 2016 by chris

[ste7ios 469]

Kharli is right. It's a permanent magnet alternator so it's output is always high depending on rpm.

 

If you don't consume it, R/R will do a short-circuit to keep the voltage down...