Dan
Premium Member
Registered: 22nd Apr 02
Location: Gorleston on Sea, Norfolk
User status: Offline
|
im doing an iva for my btec in hgv mechanics.
one of the questions is, why does air/fuel mixture change during acceleration from tick over.
i have evidence that a deisel clio has an tick over ratio of 16.8:1 on tick over
on acceleration it goes to 21.4:1
i need to know why??
thanks
Adult GiftsClick here to vist us
|
Half Pint
Member
Registered: 25th Mar 02
User status: Offline
|
look on google for answers
|
Dan
Premium Member
Registered: 22nd Apr 02
Location: Gorleston on Sea, Norfolk
User status: Offline
|
ive done this, asked people in the workshop, nobody can see why.
its a bit more in depth than any of them have done.
people keep saying, its because you need more fuel to go quicker, but thats not what im after, as fuel always stays as one part, the air % increases not the fuel
Adult GiftsClick here to vist us
|
Greg_M
Member
Registered: 2nd Sep 03
Location: Grantham, Lincolnshire
User status: Offline
|
quote:
Originally posted by Dan
people keep saying, its because you need more fuel to go quicker, but thats not what im after, as fuel always stays as one part, the air % increases not the fuel
maybe me being stupid, and i know nothing, but common sence would tell me that fuel is burnt right. so what does fire need to burn, oxygen.
|
Dan
Premium Member
Registered: 22nd Apr 02
Location: Gorleston on Sea, Norfolk
User status: Offline
|
yes, but why does the ratio of air to fuel increase when accelrating??
why doesnt it just remain the same amount of air to fuel, but just put more fuel in.?
Adult GiftsClick here to vist us
|
Greg_M
Member
Registered: 2nd Sep 03
Location: Grantham, Lincolnshire
User status: Offline
|
quote:
Originally posted by Dan
yes, but why does the ratio of air to fuel increase when accelrating??
why doesnt it just remain the same amount of air to fuel, but just put more fuel in.?
it doies put more fuel in, its a ratio, its 1 part fuel to 16.8 parts air, and then 1 part fuel to 21.4 parts air.
the fuel doesnt say at the same level, the ratio od air to fuel increases as the fuel is being burnt at a faster rate
|
Greg_M
Member
Registered: 2nd Sep 03
Location: Grantham, Lincolnshire
User status: Offline
|
say at tick over, to burn one ml of fuel it takes 16.6 ml of air to burn, but under acc it takes 21.4 ml of air to burn 1 ml of fuel. it the demand for oxygen
|
Dan
Premium Member
Registered: 22nd Apr 02
Location: Gorleston on Sea, Norfolk
User status: Offline
|
yes, i made a mistake, should say why not just put more of the air/fuel mixture in...
yes, the amount of fuel increaes...but why do they put more air with that fuel than they would if it was just ticking over??
Adult GiftsClick here to vist us
|
Corsa E-Tec
Member
Registered: 4th Feb 04
Location: Stevenage Drives: Leon Cupra
User status: Offline
|
i did this in clollage 6 years ago, i'm thinking, so this could be wrong,
At tick over your not engaging any gears so there for no pressure on the engine so fuel and air mixture is low, but when engaging gear the fuel and air mixture is increased to give a bigger/harder explosion (in cylinder on bang stage) to make the valves,crank,shafts,wheels move.
|
Dan
Premium Member
Registered: 22nd Apr 02
Location: Gorleston on Sea, Norfolk
User status: Offline
|
quote:
Originally posted by Corsa E-Tec
i did this in clollage 6 years ago, i'm thinking, so this could be wrong,
At tick over your not engaging any gears so there for no pressure on the engine so fuel and air mixture is low, but when engaging gear the fuel and air mixture is increased to give a bigger/harder explosion (in cylinder on bang stage) to make the valves,crank,shafts,wheels move.
right...
the mixture is lets say 16 litres of air to 1 litre of fuel
when it accelerrtates the mixture then goes to say...21liotres of air to 1litre of fuel.
so its putting 5 more litres of air in
y?
Adult GiftsClick here to vist us
|
Greg_M
Member
Registered: 2nd Sep 03
Location: Grantham, Lincolnshire
User status: Offline
|
quote:
Originally posted by Dan
why not just put more of the air/fuel mixture in...
there will be an increase of both its a ratio it wount just burn off 1 unit, that same as at standstill. at standstill t mayb burn say 14units per minute,
but under acc it may burn 114units per minute. its a ration for the amount need for one unit.
quote:
but why do they put more air with that fuel than they would if it was just ticking over??
driving the engine, resisting against inertia ect and not just ticking over.
|
Dan
Premium Member
Registered: 22nd Apr 02
Location: Gorleston on Sea, Norfolk
User status: Offline
|
only thing i can think is, there will be more oxygen in, meaning the combustion will be more powerful.
Adult GiftsClick here to vist us
|
Corsa E-Tec
Member
Registered: 4th Feb 04
Location: Stevenage Drives: Leon Cupra
User status: Offline
|
thats what i was thinking, the more air, the more compression when the cycle goes into squeeze so then the bang will be bigger.
thats what i tried to explain in the last post, the long winded way 
[Edited on 16-02-2005 by Corsa E-Tec]
|
bradfincham
Member
Registered: 20th Sep 02
Location: East Of England Drives: Clio 172
User status: Offline
|
also worth noting that when at tick over the air fuel ratio is stoichometric, close to lamda one, and when you accelerate this changes and increases. Which is why you need more air and more fuel to deliver the power, so for a short while you will go over rich beyond stoichomteric
|
LukeGSi
Member
Registered: 9th Dec 03
User status: Offline
|
I know the answer.....
|
Dan
Premium Member
Registered: 22nd Apr 02
Location: Gorleston on Sea, Norfolk
User status: Offline
|
get out 
Adult GiftsClick here to vist us
|
Dan
Premium Member
Registered: 22nd Apr 02
Location: Gorleston on Sea, Norfolk
User status: Offline
|
so does more oxygen increase the power of an explosion??
obviously to much will make it to lean, but the an extra bit will make it a larger Bang so to speak?
yes?
Adult GiftsClick here to vist us
|
Corsa E-Tec
Member
Registered: 4th Feb 04
Location: Stevenage Drives: Leon Cupra
User status: Offline
|
yes, thats my theory!
|
Dan
Premium Member
Registered: 22nd Apr 02
Location: Gorleston on Sea, Norfolk
User status: Offline
|
thankoooo
how the hell can i explain how emissions vary over cruising, tick over and accelerating, i cant find any info
Adult GiftsClick here to vist us
|
stuartmitchell
Member
Registered: 24th Apr 04
Location: Kirkliston, Edinburgh
User status: Offline
|
I always thought that on acceleration the fuel/air mixture is increased because the cams are opened up more
Like V-tech especially DOHC engines, when accelerating hard and using the higher rev range they use shoot loads of fuel 
Ive probably missed the point
|
Dan
Premium Member
Registered: 22nd Apr 02
Location: Gorleston on Sea, Norfolk
User status: Offline
|
yes...were on about the mixture, as in how much air goes in with the increased fuel input.
Adult GiftsClick here to vist us
|
Corsa E-Tec
Member
Registered: 4th Feb 04
Location: Stevenage Drives: Leon Cupra
User status: Offline
|
tick over throttle butterfly is at normal, so there for letting in a steady amount of air.
cruising the butterfly is say half open so letting in a steady, but yet more air.
but when accelerating the butterfly is wide open,sucking in masses of air!
the more air and fuel through each stage the higher the emissions.
I think may jog ya brain a little
Brad should know, he's at uni
[Edited on 16-02-2005 by Corsa E-Tec]
|
Dan
Premium Member
Registered: 22nd Apr 02
Location: Gorleston on Sea, Norfolk
User status: Offline
|
thats reminded me...but i need to explain what changes in the emissions and i cant find nothing, i got to get a distinction, cos then ill get a dd overall!!
Adult GiftsClick here to vist us
|
Corsa E-Tec
Member
Registered: 4th Feb 04
Location: Stevenage Drives: Leon Cupra
User status: Offline
|
DD, what, u getting breast implants
|
bradfincham
Member
Registered: 20th Sep 02
Location: East Of England Drives: Clio 172
User status: Offline
|
email sent dan
|
