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I think that details of fuel efficiency ( = energy-efficiency --well, almost) should be covered in articles about say automobiles, the steel industry, railroads, etc. Then under each of the headings of transportation, industry, commercial, and residential, there should be a subsection on energy efficiency (includes fuel efficiency). For transportation, this would compare the energy efficiency of various modes of transportation and briefly explain why some modes are sometimes more efficient than others. Then "fuel efficiency", "fuel economy", "energy efficiency", "energy efficiency", etc. would all link to a common article which would define the terms, etc. (something like what I've done under "Energy efficiency terminology"). It would have a lot of links to articles about energy efficiency for a specific activity such as transportation, railroads, industry, aluminum production, etc. DavidLawyer 22:23, 14 June 2006 (UTC)
I don't see why this article should be exclusively about fuel efficiency of vehicles. The concept of fuel efficiency applies to any machine which does work. A section on power stations would also be useful. I added the trivia on the space shuttle and humans because it's interesting. Yes, food energy is not interchangeable with gasoline. But equally gasoline is not interchangeable with diesel or hydrogen. Seabhcán 15:20, 23 February 2006 (UTC)
This page is about Fuel Economy instead of Fuel Efficiency. Although the author does explain the difference between the two in the first paragraph, the rest of the article is about Fuel Economy. The problem for me is that readers get confused because the first paragraph is in contradiction with the rest of the page.
In my opinion the whole article apart from the first paragraph should be renamed to Fuel Economy and this page should explain more about causes and effects of Fuel Efficiency.
But fuel efficiency is not related to engine displacement. In my opinion it tells you how much energy can be extracted from a certain amount of fuel. When the power output of 180 hp is really applied it will use a lot more fuel then the 120 hp did at maximum power so you would have to calculate the amount of fuel the 180 hp engine would use at a 120 hp output to be able to say anything about fuel efficiency.
Hope this makes any sense.
In addendum to the most recent comment. Usually a higher-output engine uses more fuel, as was just said. The reason is that the higher-outputting engine often has higher volumetric efficiency, or ability to fill the engine with air. Part of the increase in power you mention is due to the revised intake system, which gets more air into the engine per revolution. Since you need air to burn a given amount of fuel (14.7 parts air : 1 part fuel), the engine with higher volumetric efficiency can burn more fuel per revolution and thus create more power, even if the "fuel efficiency" is the same. I think what you mean by fuel efficiency is more properly referred to as thermal efficiency, or the proportion of the energy released in the combustion process that is converted to mechanical energy to drive the car rather than lost as heat. For example, the Toyota Prius uses an Atkinson cycle engine that stresses thermal efficiency (extracting all the work from the energy produced by the burning of fuel) at the expense of volumetric efficiency (fully filling the cylinders with air). Thus the Prius is quite fuel-efficient even though the specific output is less than spectacular (something like 75 hp from 1.5 liters).
Also, a big factor in specific output is the RPM at which the engine operates. Roughly stated, an engine that revs twice as high will make twice as much power, all other things being equal. Thus the high-revving engine will have twice as high a specific output, but will burn at least twice as much fuel in the process. That's why an F1 car getting 700+ hp out of a 3L motor isn't an econocar compared to an average sedan motor which gets 200 from the same displacement. -jspater
I think everyone here has probably heard the apocryphal story about a guy who found a way to make a Camaro get 150 mpg with some secret technology but the big oil companies "silenced" him. Well I have no idea how much truth there is to this, but Wikipedia would be a great place for anyone who has a clue as to the truth of this to spread the word. If there is indeed a technology like this that would truly piss off the oil companies, let's post it up here and there will be nothing they can do about it.
Weight Minimise all the weight inside the vehicle, that means stripping out the seats, no luggage, go naked, lose weight, remove all the internal trim from the vehicle Engine Get it cleaned and tuned up, use the most appropriate engine oil, etc. I'm not an expert in car maintenance, but there are small things you can do. Driving Drive at around 55mph in the highest gear. Use the clutch when going downhill, and re-engage when you're near the bottom of the hill--Manc ill kid 12:09, 8 June 2006 (UTC)
Ucntcme 03:16, 5 November 2007 (UTC)
I have just asked a question about the format of fuel efficiency units at: Talk:Gallon. Bobblewik (talk) 13:00, 20 Jun 2005 (UTC)
Not 150 but I have been involved withn a team some time back that did achieve 108 mpg.
I think this is incorrect. The best fuel economy is if you accelerate to the most fuel-efficient speed (45-60mph) smoothly but quickly, shifting gears to keep the engine RPMs up near the maximum of the torque curve until you get to speed. Google on "ecodriving". I'm not clear enough on my engine physics to be 100% sure on this.
Years ago, Car and Driver Magazine reported on some tests by BMW that measured the net amount of gas required to get from A to B, instead of the momentary use-fluctuations at different rates of acceleration. C&D reported this: For distances of a mile or more, accelerating at about 2/3 acceleration and holding steady at the desired speed yielded better gas mileage than slow acceleration to the desired speed. Volumetric efficiency was cited in explanation.
--- In the city, brisk acceleration has a collective benefit. Even when the distance to the next light is short, moving smartly through an intersection allows more cars to get through, eliminating one or two go-stop-idle cycles for them. Obviously, there's a trade off here, but those who prefer gradual starts ought to be informed of the costs of their preference to others.
--- Since heavier vehicles with larger cross-sections are more efficient at lower speeds than lighter vehicles with smaller cross-sections, it might make sense for SUVs, minivans, larger pickups, and crossovers to be included in the highway left-lane ban for trucks, using a height criterion.
(apologies--this may show up twice--new user) Bo8ob (talk) 20:45, 15 June 2008 (UTC)
how about some info on those world records for fuel efficiency? the experimental cars that get 10,000 miles to the gallon and so on. - Omegatron 14:30, July 17, 2005 (UTC)
It might be best to set aside a whole new topic just for tips about getting better fuel economy out of vehicles.
Another section might be dedicated to fuel economy 'mods' that (at least in theory) definitely work, versus the pure quackery that gets really popular when fuel prices spike a bit.
First off, "gradual" acceleration is just wrong, if "gradually" accelerating means you're staying in first, second and third gear longer, you may as well be pouring gas onto the street. You can prove this to yourself with your car's built-in real-time mileage doohicky, or with a 'scanguage' gadget plugged into your OBD port and monitoring fuel consumption and real-time mileage. The longer you spend in lower gears, the worse the mileage you'll get. Shift toward the highest practical gears as quickly as practical, and then 'gradual' acceleration will win... once you're in 4th or 5th gear.
Also, it should be pointed out that though fuel economy is a fine goal, that we're still not in bad enough shape that you NEED to dump a perfectly good vehicle to save 10MPG with a new car. To save even 10MPG, it could take a decade, even longer to pay off the difference in a new car and a car you already owned, even at $3 or more per gallon. Of course, if you're talking trading a truck/SUV for a little car and a 30+MPG difference, then it could take less time than paying for the car to make up the difference with only a modest increase in fuel prices, especially if you have little or no 'equity' in a truck/hybrid you're making payments on. The more you drive, the quicker any savings add up.
Potentially Expensive Fuel Savings:
1. Get a car that is fuel efficient to begin with.
2. When you get your efficient car, get a manual transmission. However smart an automatic transmission's 'brain' is, it can't see the road ahead like you can, and it can't predict what gear to be in as intelligently, as a result.
3. Get a car with real-time fuel consumption monitoring, or buy an add-on like a '[Scangauge]' to use until you've established the optimal driving patterns for your vehicle.
4. Don't get a car that keeps the A/C on all the time to keep the windows 'clear', or with 'climate control' that maintains a preset temperature without giving you explicit control to turn the A/C absolutely off, even with the vent fan ON.
"Free" Fuel Savings:
1. Keep track of your fuel consumption. A notepad and a pencil will do. A simple log of odometer+how much gas you put in, with whatever accuracy the odometer and pump gave you. You can't tell if you're saving gas if you don't keep track.
2. Check your tire pressure often, keep tires inflated properly & balanced/aligned. For safety AND economy. "Once a month" is recommended for checking pressure, but you should make sure the tires are equally and properly inflated more often than that.
3. You don't need to "pull G's" when the light turns green, and you don't need to go the speed limit (or higher) right up to a red light.
4. Time your arrival at lights so they will be green and traffic will be moving more often than not. If they aren't going to be green when you get to them, don't be in any hurry to reach them, and you won't feel so bad.
5. Manual: Coast out of gear everywhere you can safely (and legally) do so. It adds up quickly. Most states make it an infraction to drive 'down-hill' in neutral, but it's usually your most economical gear for every other situation. During extended downgrades at highway speeds, many modern engines will shut off fuel supply completely.
6. Keep an adequate enough following distance that you can pace the car(s) ahead and virtually never brake or accelerate. (The dimwit who tailgates you now would tailgate even if you were tailgating the car ahead, and driving 100MPH.)
7. Get into the highest gear you can, as quickly as you can when accelerating.
8. Take a hill in the highest gear you can, even if it means going a little faster up-hill.
9. Off the highway, open the windows. On the highway, at higher speeds, shut them, the aerodynamic drag is worse, possibly worse than running A/C.
10. A/C is "free" when rolling down-hill, in gear. You really can live without A/C, with the vent fan on, even in 100+F temperatures. Bring some water with you.
11. Don't go excessive speeds on the highway. Don't go excessively slow, either.
12. Use the cruise control on flat, open highway. Set a sane speed, and let the computer stick to it.
13. Don't treat your car as a mobile storage shed/dumpster. Shovel the garbage and useless junk out of it once in a while. It may even stink less.
14. Keep the windows absolutely sparkling clean and residue free, and you won't need to operate the A/C as much in damp weather to keep them clear. You'll also be able to see better at night.
15. Don't drive around in parking lots looking for a spot. Half the lot is almost always empty, so look in the empty half for your spot.
Ucntcme 04:29, 5 November 2007 (UTC)
--- Cheap Savings: 1. Buy a more efficient USED car. Your outlay will be far, far less than buying one new, and may even be worth it in only a year, maybe two depending on how much more efficient it is and what the price is. Of course, this one is quite variable by country; I understand the used market in the US offers far less of a saving than in the UK, for example... overall, at least in my position (living in Britain, not trying to out-bling or particularly impress anyone or win races, just survive within a limited budget), running what is now a 9-year old car makes a hell of a lot of sense, and if I can afford it on less than £14k a year, it's probably chicken feed to someone with the ready cash to consider replacing a perfectly good but slightly inefficient vehicle with a BRAND NEW one (spending several thousand in the process) on the basis of manufacturer's overinflated economy claims...
(current car cost me £2250 in january 05, quite near to the bottom of it's depreciation curve as it's a nice model ... servicing and maintenance costs about £1000 so far... no more complaints with it than a friend has with her from-new £14000 car bought jan 06 (that's not 'none', but it IS 'minimal')... in fact why buy new at all in this day and age of super endurable vehicles? Particularly if efficiency and money saving are your aim? and environment saving, as this way, you're taking ownership of something that's already been built, rather than made especially for you...)
2. Take your normal long distance / fast road driving speed and knock 5mph off it, whatever it is, if it's above 50-55 already. You probably won't notice a significant increase in driving time unless you're going a LONG way; you'll make a small but real saving in consumed fuel just from the steady speed, will work the engine less to maintain it uphill or to reach it after being forced to slow for any reason, and will spend more time in the slower lanes where you'll be less tempted to go even faster than your previous set speed because there's only the open road ahead of you, or to more quickly pull into a gap in said slower lane to move out of the way of a tailgating psychopath. Plus there's less wear on the engine, tyres, brakes and bearings, more reaction time and braking distance to avoid an accident (so long as you don't tailgate - 'drafting' trucks at 55 is a whole different issue, for the truly cash strapped and gung-ho), and less chance of a speeding ticket.
I do sometimes wonder if the so-called speeding 'problem' would largely vanish overnight if government safety agencies would stop agressively promoting the fairly disprovable dangers of it mainly to those to whom it doesn't actually apply (moderate to fast safe drivers and very slow to moderate unsafe ones) or just don't care (fast to very fast unsafe, often unlicensed or antisocial/sociopathic drivers), most of whom will never see let alone be involved in a fatal accident in their lives, and used the same TV and newspaper ad slots and roadside hoardings to just point out the financial benefits in plain terms... something everyone can relate to. - Tahrey 13/1/07
Preliminary apology:
I apologize for the Wikipedia ineptitude displayed. This is the first time I have been here. I don’t know how to do this.
I found this on Wikipedia:
"Avoid driving at excessively low or high speeds. Most gasoline powered cars operate with maximum efficiency in the range of 45 to 60 mph ( 70 to 100 km/h ). This effect is largely due to aerodynamic drag. For vehicles with greater frontal area and less streamlined shapes (SUVs, trucks) best fuel economy is typically obtained toward the lower end of this range."
I think the above is garbage I am a mechanical engineer. I have some experience with automobiles, and I have driven one for many years. Who writes this stuff? Where is their data or theory? How can it get changed?
What does "maximum efficiency" mean? Is that distance per unit of fuel or is it distance per dollar including driver time and "My time ain't cheap?"
I think this is stuff written to justify wacko driving. unsigned comment by Ecar 12:43, 23 September 2005
re: Ecar ... explain your 'wacko driving' comment? You mean anyone who drives slower than you wish to, I assume, rather than the other more extreme/potentially dangerous examples on here of e.g. 'slingshotting' (or pulse-and-glide). I too get frustrated at slow drivers on fast roads (particularly when there's very limited opportunity to get past them), but the full force of my ire is now saved for the truly slow ones (35mph or less) once I did some bottom-dollar essential driving at low speeds and was surprised at how long each precious gallon lasted, and did some (rather unscientific and unrepeated, but eye opening) testing later when I had spare cash and time. I now know those doing 40 to 55 are as likely to just be poor or economy/environmentally minded rather than lobotomised... the amount of fuel I DIDN'T use travelling a 50-ish mile test route at a steady 45mph was incredible, certainly compared to how much it would have been at 75, or even 60. I achieved something in the region of 70mpg... or nearly double what I usually managed tearing around the same stretch at 75 to 90mph... that, and similar receipts (more reliable, as greater distances were covered - on the 45mph run I barely consumed a typical gas station's minimum vend amount) for figures such as 66mpg at around 50, 59 at 55mph, etc suggest there's considerable weight to this argument, and not just the ravings of some tree-hugging nut jobs. Whether your time is more valuable than the fuel you're pumping into your car or the CO2 you're conceptually pumping out of it is a matter for your own consideration. Presently, I'd love to be getting probably 60mpg out of my slightly thirstier 'new' vehicle under a similarly disciplined regieme, but I just don't have the spare time in my life or the ability to deal with the stress that would be directed towards me for it, when I can fairly easily afford to use an extra half gallon every 40 miles. Besides, a lot of my driving is in cities rather than on the open road; in the urban area it's all you can do to try and brake early and gently to try and avoid unneccessary downshifts and stops (as pulling away from a standstill and sitting idling are big wasters) and condition yourself to use 50% throttle and the highest possible gear, as your potential maximum speed and even your ability to accelerate with any force is severely limited by lower posted limits, the terrain, and other drivers being dopey and frustratingly/inefficiently slow :) (Now, if the only available car could only manage 15-20mpg at 70mph, rather than 35-40, my long-distance speed choice might swing the other way... and i'd cycle across town even in the rain) -tahrey 13/1/07
I think it would be good to work information about fuel economy trends into the article. Here's some stuff I found so far:
--Ben 03:26, 29 November 2005 (UTC)
What about the USArmy's Multi-fuel engine? it will riun on whatever u put in it...even water but don't go looking for any great numbers...
This page is really misleading and tries to express engineering principles and laymans terms. To summarise:
Fuel efficiency is simply useful energy output divided by heat or chemical energy input expressed as a percentage. This can be calculated for any thermal plant e.g. power stations IC engines etc. It is affected by a number of factors depending on the thermal cycle and machinery used.
Depending on which camp you're in, fuel economy is the amount of fuel required to go a fixed distance (l/100km) or the distance which may be travelled for a fixed amount of fuel (mpg).
Specific output is the power output per unit displacement.
These there measures are separate and NOT related! However, factors which affect one measure may well affect another.
The efficiency page needs to be totally re-written so that it contains actual facts.
Yotboy. 192.149.117.69 13:25, 2 January 2006 (UTC)
Added external link to text "93/116/EC"
-Mardus 11:38, 8 January 2006 (UTC)
For article translators: The Directive is also available in other languages in here.
-Mardus 13:37, 8 January 2006 (UTC)
-Mardus 12:20, 8 January 2006 (UTC)
This article could be usefully expanded - it shouldn't just be about cars. Interesting questions are: Why are some engines more efficient than others? How do different types of engines compare (Deisel, Fuel Cell, electric, etc)? How do cars compare with aeroplanes, ships, rockets, steam engines, human body, etc for efficiency? How (in detail) has the efficiency of engines improved over the centuries?
There should also be short introductions and links to topics like aerodynamics as it pertains to fuel efficiency. This article is not a specialised topic and should be in layman's terms. I imagine that, with energy issues being so in the news lately, a lot of people will come looking for information on fuel efficiency. Seabhcán 11:17, 2 February 2006 (UTC)
I don't see why this article should be exclusively about fuel efficiency of vehicles. The concept of fuel efficiency applies to any machine which does work. A section on power stations would also be useful. I added the trivia on the space shuttle and humans because it's interesting. Yes, food energy is not interchangable with gasoline. But equally gasoline is not interchangable with diesel or hydrogen. Seabhcán 15:20, 23 February 2006 (UTC)
Many years ago a British car magazine set up an economy test to verify the theory that petrol (gasoline) engines are at their most efficient with the throttle open during brisk acceleration. A Jaguar car was driven for a predetermined distance at a moderate constant speed on a closed test track, the speed chosen being the most economical for that vehicle. Mpg results were noted. The test was then repeated using the "slingshot" technique, accelerating strongly to a speed well above the constant speed on the previous trip, followed by switching off & coasting in neutral down to a very low speed, then repeating the acceleration/coasting, until the set distance had been covered in approximately the same time. The result, as you have probably guessed by now, was a conclusive win for the slingshot technique. This result appears bizarre & counter-intuitive to the average motorist, who assumes that moderate constant speeds are best. I can't remember the name of the magazine, and I'm trying to find further information on this topic; can anybody help?
This test, while pointless, makes complete sense when you estimate & compare the average RPM levels of the two cases. They just misconstrue "efficiency." In the first test, the engine runs at a constant but moderate RPM for the whole test, resulting in a high average RPM. In the other test, the RPMs spike to get the car to a high speed, and then the RPMs drop to neutral while the car coasts "to a very low speed." Repeat that process for the whole test. This would result in a low average RPM, and less fuel used. This is already common knowledge.
I think it might be illustrative to think of it as extracting more power from the engine, and the fuel, whilst making more of a saving against internal friction from the engine (as it's being run at a lower average rpm, only going higher than that of the continuous-speed car for a small proportion of the time, and may well be turned off completely for a similar or longer period) than is potentially lost to wind resistance due to going faster (but then - you'll make a saving THERE when going slower also). This works particularly well if the slingshot car remains in top gear and accelerates on more efficient mid-range torque than going all-out at high rpms. As I noted some time ago at the bottom of this thread :) it's similar to the technique used in 'true' hybrids, particularly at low speeds in town, where frictional and throttling losses in the petrochemical engine are immense compared to wind resistance (which makes high speed running inefficient for any type of propulsion, but is negligble below 30mph, ironically the point where most ICE vehicles will HAVE to downshift to avoid labouring), allowing them to famously make a killing by running on all-electric power, only kicking the oil-burner into relatively wide-throttle life for a short period when the (often laughably low-capacity, but acceptable for THIS purpose) batteries drop below a certain level of charge. Unfortunately, because of the assumptions built into most carburettors and vacuum advance systems, and programmed into their modern equivalents regarding what a driver is doing according to the throttle pedal setting, a variation on this method - giving a car about as high a top gear as the engine can sustain at moderate highway speeds - doesn't work well in practice. Even though it drops the RPMs (further) into the efficient running zone, the carb/vac or ECU interprets the 90-100% wide throttle as 'accelerating hard' or 'climbing a hill', and the resultant enrichment of the fuel mix and timing alterations (maximising total power output, but not output per consumed unit volume of fuel) negates the saving from lower RPM, higher torque and less throttling loss rather than adding to it, particularly as this is now the steady state rather than a blip. (Despite someone with better engineering knowledge than me arguing against it, I did once fit a slightly underpowered car with the turbo variant's gearbox, thinking - with the backup of a careful mathematical check - it would improve the cruising mpg still further from the standard... though it was a fair bit quieter and more comfortable, the consumption remained much the same and possibly decreased, given that full throttle now only sustained about 75-80mph in top instead of 90). It does however seem to work well for diesel engines, probably explaining some of their efficiency (lower rpms, better torque but similar or less power meaning a wider throttle setting, and less obstruction to the inlet path as the fuel is injected directly to the cylinder or inlet manifold rather than in an identifiable throttle body) ... I guess their fueling setup must be administered differently, and of course, there's no ignition to advance or retard... (also it did the business for the Insight, which had higher gears on it's 1.0L + occasional electric boost engine than my 'economy' 1.6L has - Honda must have reprogrammed it quite comprehensively) ... Hmm, that gives me an idea for a different yet similar project with a diesel and a scrap lift winch motor, when I once more have the time and money :D - Tahrey 13/1/07
How come only European subcompacts are mentioned. Less than 18% of cars in Germany are subcomapcts, so shouldn't the fuel economy for the average Euro Car, such as a Passat Diesel, be added to the page. It seem rather POV to compare a subcompact to an Impala and an Expedition. Thanks for contributing. Gerdbrendel 18:38, 10 February 2006 (UTC)
Please keep it to third person. The idea is to inform the reader, not tell the reader what to do. That's Wikibooks' job. Elle vécut heureuse à jamais (Be eudaimonic!) 05:20, 13 February 2006 (UTC)
Naturally aspirated engines tend to be more fuel efficient than engines with forced induction (ex: turbocharged, supercharged).
From the little thermodynamics and engine theory I know, this statement seems incorrect. Turbochargers use waste energy in the exhaust to presurize the intake, thereby overcoming throttling losses (which are about 15% at cruise power). Whereas in a normally aspirated engine the pistons have to suck air into the cylinders, using up real power, a turbocharged version of the same engine would have no losses to this suction, and get that energy for free.
Can someone illuminate?
Maury 22:42, 7 March 2006 (UTC)
Only by example, a friend of mine wanted to fit a turbocharger to his car then decided against it because the fuel economy would be too costly for him. ( ok the excitement working for a racing team went to his head!) So from that I guess it must be true. Someone else can explain the theory, I should think it has to do with 'backpressure' config.
---
This is another one for those arguing volumetric vs thermal efficiency, or whatever it was. The turbocharged car drags more useful power from the engine (same displacement, more grunt) and the fuel (using more juice, but producing disproportionately more push from its combustion), but tends to get used for more inefficient uses (high speed running, WOT acceleration etc) and suffers other inefficiencies that can hurt it in normal use (particularly in town) or when idling (lower compression ratio when off boost, higher compressive friction when on it, altered fuelling and ignition maps, using more fuel to satisfy lambda requirements coming from more air entering the cylinders etc)... not to mention the drag from the turbine itself and the longer intake path, particularly if an intercooler is used.
(BTW your missing part in the air movements part is the drag felt by the cylinders as they push the exhaust out through the port... though there's not too much of it as it's mainly decompressing having been heated to several hundred degrees, it's still got some backpressure effect from the vanes of the exhaust turbine)
Unless it's offering a spectacular amount of boost, the overall economy cost isn't so great - though it is noticable - and the effects resulting from it could be described as 'worth it' :)
(More consisely (sp?) - it makes the original engine less efficient overall and is detrimental for light duty applications, but improves the amount of work done per volume of fuel under load)
Examples: 1272cc Volkswagen MPi engine, non-boosted version puts out 75hp; boosted G40 variant (technically supercharged, but subject to similar arguments) gives 113hp and similarly increased torque from essentially the same components, but with a thicker head gasket, altered ECU map and a compressor. On-the-road performance is noticably increased, and when being driven hard doesn't eat *too* much fuel (though it's still not exactly wallet or eco friendly!), and is certainly competitive in this area with larger displacement unboosted engines - but it does lose a few MPG compared with the NA model when cruising at legal speeds and has definitely unenviable (for a 1.3...) economy across town.
On the other hand, I have heard of caravan owners who have justified fitting turbos to their saloon cars to their insurers as safety and economy improvements to the vehicle, allowing them to pull onto busy roads more briskly and traverse inclines at higher steady speeds (with less danger from overtakers and less risk of overheating the engine at high rpms) without having to invest in a different, possibly larger/more prestigious (and therefore more expensive to buy and run) vehicle with an inherently meatier and drastically more thirsty engine. Again the arguments are a bit moot when cruising with/without trailer around town or at steady highway speeds on flat ground (the turbo in this case requiring the RV's justification to be more than a tyre-spinning toy :), but the device comes into it's own when sustained high power is required, helping the user tour more efficiently and swiftly without using a bigger and (comparitively) inherently less efficient engine.
... and not for nothing is the Turbo Diesel the powerplant of choice for those who haul big loads for a living (truckers, bus and van drivers, etc), with the non-turbo variation being largely forgotten except for those seeking ultimate economy (with performance a very distant second priority) in smaller vehicles.
I don't need one myself, I don't drag large weights about and can already go as fast as I presently dare to (90~100mph depending on gradient) without either a big engine, a compressor, or even running WOT more than 50% of the time, so the fact of it making larger power outputs more cost effective is neither here nor there.
Clarifications, edits, what have you, from people who actually know anything about this rather than relaying other things they've been told or have read and adding educated guesses, would be most welcome.
--- tahrey (i will eat this thread hehe... i must get off the net i think) 18/4/07
It's not fair to compare the miles/gallon of the Space Shuttle with those of cars and trains (that don't have to work against gravity). One more meaningful measure would be fuel consumption vs. potential and kinetic energy gained. StefanoC 08:45, 13 March 2006 (UTC)
Fuel efficiency is not expressed in terms of power per unit of engine displacement. Meggar 01:09, 5 April 2006 (UTC)
There has been no comment on this on either page in the month since the tag was put up. Here is one for Oppose. PS, tag removed by another user. Meggar 01:48, 27 July 2006 (UTC)
Do my eyes deceive me or does that final table seriously suggest that, on average, private cars and motorbikes are the most efficient forms of transport? Either there's some revolutionary idea in there, public transport in the USA is BADLY undersubscribed, or someone's paying off the DOT's research division... Also, regarding the "slingshot" idea - this is why, in part, hybrids can get better economy, as in an ideal situation the mean power output would be the same, but the gas engine would only be used to charge up the batteries, running at a low and efficient rpm with near- or completely-wide open throttle for minimal losses (kept at the lower speed by the load from the regenerator), with all running power coming from the electric motor alone; the gas engine turning on only when the batteries start running low, and turning off again once they're topped up. Obviously that's more for the DIY feats of engineering than a current road car, as the battery packs (and electric motor specs) are laughable and the control systems are not aimed at this end. However a variant on the slingshot technique known as "pulse and glide" has been known to help economy amongst Prius drivers - it takes advantage of certain distinct motor-on and off points and system reactions to user input to deliver noticably greater fuel economy with an average speed of around 35mph ("pulsing" up to about 40 with the motor at fairly wide throttle, and "gliding" back down to about 30 with either zero power, or only the electric motor being turned on). Obviously it's not a good idea for safety or road manners, and it can be argued that a large part of your economy comes from forcing yourself to run at only about 35mph (which, certainly amongst some uk workers in low paid jobs (ahem - NOT only myself), is a recognised method of squeezing the last few drops in the tank that little bit further until payday/the filling station)..... but its certainly an interesting technical case in point.
Experimenting with my current car - 1.6 SPi Opel/Vauxhall Astra (Pontiac Le Mans) 1998 - I've found the only way to maintain fuel economy is not to rush around and to drive calmly. There's not much I can do to it to "improve" it even with coasting etc.. it's just an inefficient design! ...however it IS the most efficient inamongst its immediate family and peers, including some with 1300, 1400 or 1500cc engines and full multi-point injection. A smart focus on making the engine torquey (and therefore very responsive and effortlessly accelerative at low speeds) rather than ultimately powerful (something rarely actually required of a general use road car; it's "weak" 69bhp is still more than adequate for 110mph) means the driver doesn't waste fuel revving it into the higher ranges to pull it from a standstill, even though it is mated to a high range gearbox (another good blow for economy - it revs lower at intra/intercity and cross-country highway speeds than most, sitting nicely in the torque range with just a very slightly wider throttle setting). Too bad the metalwork of the engine itself is stone-age, and the body is heavy, wide, and although sleek, not super aerodynamic. Hybridisation is a nice idea, but it won't solve all problems - now that we're finding clever ways to make a normal sized car seem enormous internally, the exterior size needs to come down, along with the weight (and the shape made more aerodynamic, like an insight or calibra), and the engines built - rather than programmed and tuned - as lightly and efficiently as possible (including making the capacity a whole lot lower and dropping the current resurgence in bhp-figure obsession), if not altogether removed in favour of electrification.
For some reason, Eric Kvaalen (talk · contribs) has removed the fully referenced data in the energy content table and replaced some of it with less reliable online sourced information. This has also left some parts of the table entirely empty. The fact that he doesn't personally have access to the industry standard reference manual from which the data was taken does not justify removing data that wiki, by definition, considers more reliable. I haven't reverted his edit this time, but I do believe that it is actions such as his that undermine the fundamental validity of wikipedia. --Athol Mullen 21:17, 9 March 2007 (UTC)
The RON number minimum for regular unleaded fuel is much higher than the minimum. The minimum I've seen in several states is 87. Someone able to justify the 91 octane number being "minimum"? Ucntcme 03:19, 5 November 2007 (UTC)
In UK / Europe the RON numbers are different again. For the UK, regular unleaded is 95 RON and super unleaded is 98 RON (although that is much rarer in recent years). Warmington (talk) 13:36, 10 November 2011 (UTC)
The C-Train in Calgary, Alberta, Canada is entirely offset by a wind farm south of the city. —Preceding unsigned comment added by 208.38.1.1 (talk) 20:33, 18 September 2007 (UTC)
To me the article implies that the increase in energy content is responsible for the majority of economy differences between gas and diesel. The clear dominant factor is the 50% better efficiency - extracting more energy from the source material. Clearly, 10% more energy in the fuel can not produce a 40% increase in economy, but getting half again as much out of the fuel certainly can. Anyone up for improving the wording there, or shall I? Ucntcme —Preceding comment was added at 04:35, 5 November 2007 (UTC)
In a related matter, does anyone think that fuel economy should be kept out of the automobile infoboxes? Please voice your opinion at http://en.wikipedia.org/wiki/Template_talk:Infobox_Automobile#Vote_on_Fuel_Economy_in_the_Infobox 198.151.13.8 (talk) 18:28, 7 May 2008 (UTC)
CCPP with natural gas have 58% efficiency in electric power production. New planed CCPP should even exceed 60%. The only car known by me in all versions is the Renault Kangoo. Here a study about the efficincy with gasoline, diesel, natural gas and electric power version Cleanova 2. --Pege.founder (talk) 10:19, 30 May 2008 (UTC)
Why haven't the numbers for E85 (85% Ethanol, 15% gasoline) been added to the chart? —Preceding unsigned comment added by Bizzybody (talk • contribs) 04:10, 4 September 2008 (UTC)
In the UK, and most of Europe, regular unleaded is 95RON. Premium is 97/98/99RON.
Is there place for methane in the table? According to http://www.littleredbook.com/fuels.html methane has 23,875 Btu/lb —Preceding unsigned comment added by 89.79.66.46 (talk) 09:53, 7 September 2010 (UTC)
Riian.januarianto (talk) 20:43, 20 February 2012 (UTC)
if we talk about the fuel efficiency, what if we discuss a little about the gasoline / diesel fuel combined with electric power and make a hybrid vehicle.
The comment(s) below were originally left at Talk:Fuel efficiency/Comments, and are posted here for posterity. Following several discussions in past years, these subpages are now deprecated. The comments may be irrelevant or outdated; if so, please feel free to remove this section.
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== More on "accelerate as gradually as possible ==
Years ago, Car and Driver Magazine reported on some tests by BMW that measured the net amount of gas required to get from A to B, instead of the momentary use-fluctuations at different rates of acceleration. C&D reported this: When traveling for distances of a mile or more, accelerating steadily at about 2/3 acceleration and holding steady at the desired speed yielded better gas mileage than slow acceleration. Volumetric efficiency was cited in explanation. |
Last edited at 20:37, 15 June 2008 (UTC). Substituted at 15:41, 29 April 2016 (UTC)
In India only kilometres per litre is used. We don't use any other system — Preceding unsigned comment added by 14.141.84.194 (talk) 18:15, 20 May 2016 (UTC)
As of August 2016, merger of the engine efficiency article into the fuel efficiency article would probably work well, if anyone wants to spend the time. I may do it sometime if the spirit moves me. — ¾-10 01:45, 12 August 2016 (UTC)
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The recently added table titles "effect of weight" is flawed in various ways, which is why I'm removing it. First of all, it is totally unreferenced, and in its form, original research. The selected vehicles are all US market vehicles, but it remains uncertain how these are configured; for instance, A VW GTI (I know that on the US market a Volkswagen GTI is a Golf VIII, but most readers don't) could be any compact Volkswagen car (up!, Lupo, Polo, or Golf); is the Volkwagen 2-litre engine a 1968 cm³ or 1984 cm³ unit? Next, the list doesn't give any clue about the standard used for determining the fuel consumption (i.e. it doesn't allow comparing with other fuel consumption figures which effectively renders the entire table useless), but most importantly, vehicle mass is only one factor out of several factors that have an effect upon driving resistance and thus fuel consumption (e.g. mass-induced drag, air-induced drag, acceleration-induced drag, incline-induced drag, energy losses in the gearbox, …). The drag induced by a vehicle's size and shape (i.e. air-induced drag) has, at speeds beyond 80 km/h, a much greater effect upon fuel consumption than vehicle mass. At speeds beyond 200 km/h, the mass-induced drag becomes so small compared with the air-induced drag that it's almost negligible. The non-inclusion of the air-induced drag alone also renders the entire table completely useless. Best regards, --Johannes (Talk) (Contribs) (Articles) 18:19, 21 September 2022 (UTC)
One additional thought of mine: The fuel consumption figures are also very unrealistic in the sense that they are way too high! There is just no way that a 2-litre VW Passat has a fuel consumption of 9.41 l/100 km. In a realistic Passat with the bog-standard 2-litre engine, the fuel consumption is in the 4 to 5 litre range, but an experienced driver can easily obtain a figure in the high 3s. The rated fuel consumption for the Passat 3G with the 2-litre engine and the six-speed manual gearbox is 4 l/100 km according to 80/1268/EEG, which makes a lot more sense than 9.41 l/100 km. And, by the way, the precision of that figure is also too high; it should be 9.4 and not 9.41… --Johannes (Talk) (Contribs) (Articles) 18:31, 21 September 2022 (UTC)
@Derek - the reason it 'works' is that a vehicle's mass is loosely correlated with its size, and which is loosely correlated with its aero drag. But the numbers you get are crazy, my 2400 kg SUV gets 9 l/100, the sticker says 7.8. I suspect you'd get better correlation if you used the city fuel consumption figure rather than combined. As Johannes says, huge tables of unreffed data are OR, which is deprecated. Greglocock (talk) 22:46, 21 September 2022 (UTC)
@Derekburgess: The reason why you couldn't find information on the subject is because vehicle weight doesn't have that much of a direct effect on fuel consumption. The reason why mass and fuel consumption seem to have a first order correlation was very well explained by Greglocock: Heavier vehicles tend to be bigger, and thus induce more driving resistance. The fact that mass actually doesn't have that much of an effect on fuel consumption can be well observed in battery electric vehicles. They are overproportionally heavy because of the lithium-based batteries they use. If mass actually had a serious effect on fuel consumption, car manufacturers would find ways to make their battery-electric cars lighter in order to obtain better milage. But they don't have to do that (and there's regenerative breaking, but that's a different story). Now, making estimates of vehicular fuel consumption based on vehicle mass is probably as useful as making such estimates based on the tyre brand, number of doors, or paint colour. There are many factors, and I could easily name several very lightweight cars with ridiculous fuel consumption figures (Trabant 601, Goggomobil, VAZ-2101, Ford Model T, MG MGA, …). But even if we make a simple model and limit ourselves to just air-induced drag, and mass-induced drag, we can easily see that mass doesn't play that much of a role beyond a surprisingly low speed. Drag can be seen a force that acts on the vehicle and thus increases its fuel consumption. To illustrate this, I use the BMW E28 (of course I do), which has the following technical specifications:
As I suggested, we can now determine the speed at which air-induced and mass-induced drag are equal:
So as soon as I drive faster than 74.4 km/h, the air-induced drag plays a greater role than mass in terms of fuel consumption. As we can easily see from the previous equation, the air-induced drag depends on speed raised to the power of 2. So driving slightly faster already has a tremendous effect. And if we now solve for drag instead of speed, and use the E28's top speed of 50 m/s as an extreme example, then we get this:
So if we actually drive with a speed of 180 km/h in a BMW E28, the air-induced drag has an almost six-times greater effect upon fuel consumption compared with the mass-induced drag. Even if we drive at a much more reasonable speed of 122.4 km/h, the air-induced drag is still 2.7-times greater (and thus has a 2.7-times greater effect upon fuel consumption) than mass-induced drag. This means that if at a speed of 122.4 km/h the fuel consumption is 7 l/100 km, only 1.9 litres are caused by the mass – the remaining 5.1 litres are caused by the unaerodynamic shape of the BMW E28.
Well, this has become a lot, but I hope that this simple comparision alone is sufficient for illustrating why mass doesn't have that great effect upon fuel consumption. Best regards, --Johannes (Talk) (Contribs) (Articles) 20:01, 22 September 2022 (UTC)
Be careful when comparing lorries with cars; lorries are substantially heavier than cars, which is why their mass is less insignificant. For a three-axle lorry with a conentional two-axle trailer we can assume the following technical specifications:
We can see that the air-induced drag is still bigger than mass-induced drag, but not as much as it would be in a car. A tractor-type lorry typically has better aerodynamics, so, in certain situations, fully laden lorries can actually have more mass-induced drag than air-induced drag. Nonetheless, lowering air-induced drag is a huge deal in the transport business. For this reason, several three-axle trailers for tractor-type lorries are equipped with huge spoilers to improve aerodynamics. Best regards, --Johannes (Talk) (Contribs) (Articles) 08:50, 23 September 2022 (UTC)
WP:NEOLOGISM. fgnievinski (talk) 03:15, 18 November 2023 (UTC) fgnievinski (talk) 03:15, 18 November 2023 (UTC)
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