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Vitorio
464 posts
12 months
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UK952 said: That's heavy air  Tony The math suggests it might be even more, although my calculation does not account for the stuff other then octane in fuel and incomplete combustion. Vitorio said: Ok, i'm gonna do the math now (not a dig at you, just getting sucked in here)
Let's assume for a while that petrol is 100% octane, or C8H18. Octane would weigh 114 grams per mole, or 8.8 moles per KG. One Mole of Octane would produce 8 Moles of CO2 (assuming perfect combustion), so one Litre of pure octane would produce 70.2 Moles of CO2. One Mole of CO2 weighs 44 grams, so 3087 grams of CO2 from one litre of pure octance.
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windy1
218 posts
120 months
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Peak torque rpm & area under the curve is where economy is at providing you are not using the torque.
Study some torque graphs with the above in mind and it will all make sense.
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Derek Chevalier
667 posts
42 months
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Fox- said: which had very impressive fuel consumption figures. When new
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Mave
1,030 posts
84 months
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moreflaps said: The thermodynamic efficiency is similar since the exhaust gas temperature in a turbo is only slightly lower. The gain comes from the power to weight ratio.
Cheers Have you got any TS diagrams to illustrate? I would have expected the exhaust gas temperature on a small turbocharged engine to be higher than a large NA engine at a given power output?
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Scuffers
10,417 posts
143 months
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as somebody that has both engines, I can tell you for a fact that the 3.0TV6 is more economical than the 4.2V8.
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UK952
580 posts
128 months
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Vitorio said: Was just thinking fuel is about 750g and a 50 litre bin bag when full of air is nowhere near a kg
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BeefMaster9000
49 posts
93 months
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The_Burg said: How does one litre of fuel, (1kg ish), produce 2.3Kg of CO2? back of fag packet calcs: 1 litre of fuel = approx 0.7kg mass of carbon within said litre of fuel ~ 0.86 * 0.7 = 0.6106kg CO2 by molar mass = 44 (12 Carbon & 32 Oxygen) therefore approx proportion of carbon in the CO2 emitted = 27.27% thus total mass of CO2 produced per litre of fuel consumed = 0.6/0.2727 = 2.2 do correct me if I'm wrong
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Vitorio
464 posts
12 months
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UK952 said: Was just thinking fuel is about 750g and a 50 litre bin bag when full of air is nowhere near a kg At atmospheric pressure/room temp, one mole of gass is 22.6 litres, so the 70 moles of CO2 i calculated for one litre of fuel (or 53 for 750g of fuel) would be near 1000 litres of co2. Also, you cant weigh a garbage bag of air, since its air displacement/bouyance in air is the same as the weight of the air in the bag. Think of trying to put a water baloon on a scale at the bottom of a pool.
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underphil
162 posts
79 months
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windy1 said: Peak torque rpm & area under the curve is where economy is at providing you are not using the torque.
Study some torque graphs with the above in mind and it will all make sense. People often say this, but is clearly untrue. EG, The max torque on my n/a petrol is at 4000 rpm So if I'm driving at a constant 40mph which will give the best fuel economy? In 6th gear at about 1500rpm or in 2nd at 4000rpm ? The answer is 6th by a massive mpg margin ...
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Buzz word
1,855 posts
78 months
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BeefMaster9000 said: Buzz word said: Anyway effecient in this context probably means lower c02. That does not always mean better MPG. GroundEffect said: You can leave it at that if you like, but to put it simply...no consideration of CO2 emissions in that comparison. FFS. A petrol engine will produce just over 2.3 kg of CO2 for each litre of petrol it consumes. This is a fixed relationship based on the chemistry of the fuel. No magic can alter this relationship, the only way to emit less, is to use less fuel. Fact. No if you take a simple view of petrol being burnt in open air like a chemistry textbook maybe. All combustion is not complete and some after treatment systems have different requirements. Take any car fitted with a cat for example: There is a rich phase after startup to get the cat warm using more fuel. However when warm it will change the exhaust gas into other compounds. The restriction itself in the exhaust creates powerloss which makes the fuel consumption higher. They are there as they reduce co2. There is alot of money invested by manufacturers fitting that as it works and lowers emissions. or atleast moves the compounds aboit a bit to the prescribed allowances. DPF regens on diesels actually require an injector in the exhaust to put fuel in after combustion. That fuel is not going to motive power so is ruining MPG. These technologies and many more work, they reduce co2 figures. If your assertation was correct to meet emissions legislation all engines would have done is get smaller. Look under the bonnet there is a ton of after treatment technology to make the burn cleaner and most of it hurts the MPG. Other advances claw it back by making sure what is burnt goes into motive power like low friction valve trains, atkinson cycle etc.
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J4CKO
7,394 posts
69 months
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I think the main factors are it takes a set amount of power to accelerate a given mass, the engines efficiency is a small percentage of this, some are better than others but any modern injected engine will be broadly similar, the problem is the thing pressing the accelerator and the ability of the engine to provide a higher rate of acceleration, basically, if it is there to use we use it, can't have your cake and eat it with physics.
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jason s4
1,611 posts
39 months
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Mouse1903 said: My 1.4 Turbo (160BHP) is 5MPG more economical than my old 1.6 N/A (127BHP) You aint driving it properly then! 
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UK952
580 posts
128 months
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Vitorio said: At atmospheric pressure/room temp, one mole of gass is 22.6 litres, so the 70 moles of CO2 i calculated for one litre of fuel (or 53 for 750g of fuel) would be near 1000 litres of co2.
Also, you cant weigh a garbage bag of air, since its air displacement/bouyance in air is the same as the weight of the air in the bag. Think of trying to put a water baloon on a scale at the bottom of a pool. Fair enough, was thinking about the 14:1 analogy earlier in the thread, rather than the moles. (I abandoned a level chemistry) If I took my garbage bag of air into a vacuum I think it would still be quite light, but your calcs would indicate I need 20.
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BeefMaster9000
49 posts
93 months
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Buzz word said: ..However when warm it will change the exhaust gas into other compounds.. They are there as they reduce co2. There is alot of money invested by manufacturers fitting that as it works and lowers emissions. or atleast moves the compounds aboit a bit to the prescribed allowances. Sorry, that is wrong. I'm no expert on catalysts but I don't know of one which can reduce CO2 emissions. catalysts reduce the REGULATED emissions from the engine sufficiently that they fall within legal limits by the time the gasses reach the tail pipe. i.e. CO, HC, particulates, NOx, but not CO2. whilst CO2 is most certainly taxed, it is not regulated. Buzz word said: DPF regens on diesels actually require an injector in the exhaust to put fuel in after combustion. That fuel is not going to motive power so is ruining MPG. actually, most passenger cars just use post injection, rather than an exhaust injector system, but the principal is the same; unburnt fuel is smattered liberally onto the catalyst, where it is burnt in the excess air which is found in Diesel engine exhaust gas, which doesn't change what i said before - a predictable quantity of CO2 is being released via the combustion of fuel and air. Buzz word said: These technologies and many more work, they reduce co2 figures. Wrong! it is doing exactly the opposite! as you said yourself, fuel sprayed onto the catalyst is non torque forming - it is being burnt in the catalyst / DPF and releasing additional CO2, for absolutely no gain at the flywheel. However, the fuel consumption / CO2 penalties for using a catalyst or DPF are unavoidable, as without them manufacturers wouldn't be able to comply with the REGULATED emissions listed above, and then they would be prevented from selling cars very quickly. It is then down to those other developments to try to counteract these increases in fuel consumption, so that the overall fuel economy of the vehicle remains competitive. This is what has led to manufacturers using transmission fluids with the viscosity of water, low rolling resistance tyres, 9 speed gear boxes and hybrid electric motors. edit to add - but if you have secretly developed a catalyst that can reduce engine out CO2 emissions - get in touch with these guys and they will pay you lots of £
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windy1
218 posts
120 months
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underphil said: windy1 said: Peak torque rpm & area under the curve is where economy is at providing you are not using the torque.
Study some torque graphs with the above in mind and it will all make sense. People often say this, but is clearly untrue. EG, The max torque on my n/a petrol is at 4000 rpm So if I'm driving at a constant 40mph which will give the best fuel economy? In 6th gear at about 1500rpm or in 2nd at 4000rpm ? The answer is 6th by a massive mpg margin ... Fancy a rolling road test to prove your theory?
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Mave
1,030 posts
84 months
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J4CKO said: I think the main factors are it takes a set amount of power to accelerate a given mass, the engines efficiency is a small percentage of this, some are better than others but any modern injected engine will be broadly similar. I think that's the basis of the whole debate. Are all engines really similar? For a given power, I'd expect a small, turbocharged engine (running with an open throttle and hence higher peak cylinder pressure) to be more efficient than a large, N/A engine (running with a closed throttle and low peak cyclinder pressure), even if you decide to neglect the frictional losses of a larger engine.....
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Fox-
9,958 posts
115 months
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Derek Chevalier said: When new
Your point being what? It only came out in 2007 so most examples are hardly ancient.
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JonnyVTEC
859 posts
44 months
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The_Burg said: How does one litre of fuel, (1kg ish), produce 2.3Kg of CO2? Well stoichiometric is 14.7:1 by mass (not volume) of air to fuel. So you are using around 15 times the mass of air to combust with the fuel and 20% of that air is the O bit of CO2.
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Derek Chevalier
667 posts
42 months
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Fox- said: Derek Chevalier said: When new
Your point being what? It only came out in 2007 so most examples are hardly ancient. Carbon build up, as mentioned previously, means the car will be down on power and economy.
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Buzz word
1,855 posts
78 months
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BeefMaster9000 said: Buzz word said: ..However when warm it will change the exhaust gas into other compounds.. They are there as they reduce co2. There is alot of money invested by manufacturers fitting that as it works and lowers emissions. or atleast moves the compounds aboit a bit to the prescribed allowances. Sorry, that is wrong. I'm no expert on catalysts but I don't know of one which can reduce CO2 emissions. catalysts reduce the REGULATED emissions from the engine sufficiently that they fall within legal limits by the time the gasses reach the tail pipe. i.e. CO, HC, particulates, NOx, but not CO2. whilst CO2 is most certainly taxed, it is not regulated. Buzz word said: DPF regens on diesels actually require an injector in the exhaust to put fuel in after combustion. That fuel is not going to motive power so is ruining MPG. actually, most passenger cars just use post injection, rather than an exhaust injector system, but the principal is the same; unburnt fuel is smattered liberally onto the catalyst, where it is burnt in the excess air which is found in Diesel engine exhaust gas, which doesn't change what i said before - a predictable quantity of CO2 is being released via the combustion of fuel and air. Buzz word said: These technologies and many more work, they reduce co2 figures. Wrong! it is doing exactly the opposite! as you said yourself, fuel sprayed onto the catalyst is non torque forming - it is being burnt in the catalyst / DPF and releasing additional CO2, for absolutely no gain at the flywheel. However, the fuel consumption / CO2 penalties for using a catalyst or DPF are unavoidable, as without them manufacturers wouldn't be able to comply with the REGULATED emissions listed above, and then they would be prevented from selling cars very quickly. It is then down to those other developments to try to counteract these increases in fuel consumption, so that the overall fuel economy of the vehicle remains competitive. This is what has led to manufacturers using transmission fluids with the viscosity of water, low rolling resistance tyres, 9 speed gear boxes and hybrid electric motors. edit to add - but if you have secretly developed a catalyst that can reduce engine out CO2 emissions - get in touch with these guys and they will pay you lots of £ I conceed co2 is more linked to fuel efficiency than co. My mistake for getting the two mixed up. I was merely offering a reason for why a 4.2 n/a on say euro 3 may appear to consume comparatively less fuel that a more restricted 3.0t on euro 5. Emissions kit could be part of that. It seems to be a point we agree on. Whilst elements in must equal elements out they are tweakable into various compounds along the way. All that hurts the mpg ecconomy. The game that is being played is people at large assume that lower emissions equal less fuel burnt and more economy. That is not necessarily true. More fuel may used so the combustion may be more complete in like for like circumstance ie the same 1.6 with all the efficiency technology v's one with all the aftertreatment and efficiency kit. It will have worse emissions but would be far more MPG efficient than it's counterpart. Ok it wont be saleable so you have to go for the emissions engine. Like in this case you could decrease capacity to improve co2 along with emissions gear and because of the emissions gear penalty on mpg end up with a smaller engine less fuel efficenient than it's predecessor just to make it burn cleaner.
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