mpg revisited

[hookie]

The pressure/temperature/volume/fuel/power output story is quite interesting. The lower the temperature of the air going into the engine should mean that when this air/fuel mixture ignites then more torque should be produced. This is because the air is colder and denser so when it expands during firing, more pressure is produced in the cylinder, hence more power. This is why intercoolers are often used in forced induction (turbo and supercharged) engines to cool the air going into the cylinders. It also probably the reason why your bike feels like it's running better in cooler weather.

[Strommer]

K8 (twin spark) did 70.5mpg over 1000 miles around le Massif Central last year - just pootling around. can't touch that with my K5.
Next month I'm off to AssenWSB witth me bro (K5). It'll pee him off at the petrol pumps when I consistantly use less with the K8.

Blimey that could save me £250 a year... nearly the excuse I need to upgrade to one of those sexy matt black K8s....

[BluesBoy]

.....engines to great the air going into the cylinders. It also probably the reason why your bike feels like it's running better in cooler weather.

looks like you've been attacked by the anti-american-word-substitution-mechanism.  

Interesting thoughts though hookie, thanks.    

I also like the sound of 70mpg!

[Juvecu]

Now that you mention it, I always did feel that the engine feels like it runs better in colder weather. Maybe I'll do a bit of research on the cold vs warm air subject, I'm a bit curious now.

[hookie]

Is this "anti-american-word-substitution-mechanism" some form of censorship created by our friends across the pond? You are right. For "great" please read "c_o_o_l". Wonder what is anti-American about this particular word? How can I switch it off? It's probably even more irritating than American spell and grammar checkers. It's about time they learned how to spell aluminium correctly!

[jeyre60152]

Going off at a tangent, the Harrier Jump Jet had water injection for the purpose of cooling to give more power during vertical take-off.

[hookie]

Not the one that crashed into the sea right in front of me at the Lowestoft Airshow bowing to the crowd a few years back. His engines were water cooled!

[jeyre60152]

That was taking it to the extreme.........

[Squirrelciv]

I always thought that it was the water content more than temperature of the air that boosts power. Apparently the water droplets in the air help dissipate the fuel in the chamber and create a better spread of vapour. It's to do with the way water and petrol don't mix.

(haven't said that very well, but I hope you get the gist )

[Juvecu]

That would make sense, colder weather often means more humidity and in more humid climates you'd probably see the same effect even when it's warmer.

I read up on intercoolers, turbo- and superchargers. Turbo- and superchargers force more air into the engine. With more air forced into the cylinder the force generated by ignition is more because there air is compressed and under pressure already. Warm/Hot air has less density, an intercooler cools the air down, cold air is more dense. So an engine will run better on cold air and cold air should have more oxygen and more humidity than warm/hot air.

I still don't know why it would use more fuel then. Would the fuel injection put in slightly more fuel when the air is colder? If so, why does it do this?

[jonH]

I think the answer lies outside of the engine and I also think there's more than one factor, e.g. your bike will take longer to warm up on colder days (can take as long as 4 mins for me on the coldest of mornings) but it's not enough on its own to be a major source of blame for increased fuel usage

I still think it's easier to slice through traffic on sunnier days, car drivers tend to be more aware of what's around them in good weather. Bad weather tends to leave them focusing on the brake lights in front of them and nothing else, so I tend to use more acceleration and brake to work my way forward.

It has to be lots of little things adding up; for me it rarely makes more than about 5-8mpg of difference in extremis.

[Juvecu]

I think that might be it for me too, riding is much smoother when the cagers can see better around them. In the warmer months the sun is out sooner and they can see if they bother to look. It's probably also a case of the motorcyclists being able to see better in the sunny months. For me, having the huge Givi screen on makes a big difference too.

[Scudnut]

No idea of MPG, I know 2 years ago I struggled to get £20 in the tank, recently I got over £27 in.
I always reset the trip and fill up at around 200 miles.

The CB100n was my first bike too, I rode it 26 miles with the choke open, thought I'd bought a lemon.

[Juvecu]

The CB100n was my first bike too, I rode it 26 miles with the choke open, thought I'd bought a lemon.

 

[Juvecu]

Figured it out: cold air = denser = more oxygen = needs more fuel to burn properly (else it's too lean.) So it makes sense (at least to me ) that the FI system would fuel a tad more when the intake air is colder.

[Strommer]

Figured it out: cold air = denser = more oxygen

Surely also more "non-burny" (excuse the technical terms) - Nitrogen.... as the proportions won't change?    Probably....