The mpg mythbusters

[Dempsek]

Article from Auto Express.simulating real world effects on MPG.

http://www.autoexpress.co.uk/news/autoexpressnews/229776/the_mpg_mythbusters.html

[Babs]

Well, considering that Auto Express is the motoring equivalent of The Sun, I'll take it all with a spoon full of salt.

There's also the fact that different cars will perform differently at different speeds/revs, a 2.0 4-pot turbo may be more economical with slightly more revs because the turbo is boosting more, and making the mixture for lean, for example.

[Richf]

, a 2.0 4-pot turbo may be more economical with slightly more revs because the turbo is boosting more, and making the mixture for lean, for example.

What??

Engines lean out on boost do they?? If they do they wont for long

Most forced cars run stoich ie 14.7/1 when off boost and richen up massively when on boost usually 12-12.5/1 at peak torque dropping into the 11's at peak rpm , some leaner , some richer but as a rough guide

[Babs]

Bad wording on my behalf...

The engines are often more efficient with higher boost levels, meaning often less fuel is used if you were to be in a lower gear for the same road speed.

Hows that?

[Kiwibacon]

Bad wording on my behalf...

The engines are often more efficient with higher boost levels, meaning often less fuel is used if you were to be in a lower gear for the same road speed.

Hows that?

More rpm is always going to cost you fuel. If you don't need the power of higher rpm then it's almost always better to be in a higher gear and lower rpm's.

I found it a bit silly in the article that they put the extra fuel consumption of higher speed down to higher rpm. Without mentioning the wind resistance at 90mph being over 3 times higher than at 60mph.

[fabia55]

what is the performance 0-60 for the quoted mpg figures

is the mpg for the quoted 0-60 time

i suspect not, it's a ply, a con.

they quote 0-60 and mpg on the same page, but are they for the same test

they should quote the 0-60 time of the quoted mpg and vice versa

[fabia55]

when should air con be used? is it not to be used? will it be unlubricated if left unused? i am bursting hot, the windows need demisting, it will be unsafe.

[Babs]

I've never found a/c to use any fuel, and it's best to run it as it's meant to be

Like some other things, use it or lose it!

[Guest]

As a "speriment" me and Mrs Estate Woman have been using the aircon almost everyday in the Fabia diesel when it's been uncomfortably hot this summer. It did make a detrimental difference to our fuel economy, but not as much as I thought it would. So they are prolly right in saying when cruising at near motorway speeds it's not an issue but most of our miles at the moment are 'in town' driving where it is more noticeable that the economy drops with the aircon switched on. Just glad I didn't order aircon for the new maxi-scooter. It's current doing 85mpg in normal use and still does near 100mph...

[Ootohere]

Nice bikes, but something like your Maxi-scooter goes to show how little Motor Cycles engines have moved on over the years as far as economy goes.

Only 223 kg in weight and only a little better in performance than modern 2 or 3 cylinder engine cars that weigh 3 times as much but can almost match the fuel economy with just a driver or maybe also a passanger..

george

[punyXpress]

When they let the tyres down, how did that effect the speedo reading?

If the distance recorded was higher that would show a false higher mpg.

[Guest]

Hi sk4, yes I agree, an area completely ignored until recently by bike manufacturers. Mine is a little heavier at 225kg as it's the high spec model which weighs in almost as much as my Vstrom 1000cc. It has the heated grips, handguards, passenger backrest, abs brakes etc etc, yet it goes really well with 0-60mph in just 7.7secs and a genuine 95mph top wack. Good for a scooter. I'm not such a speed freak now, just a freak!! It's horses for courses and the convenience of the scooter and it's performance and economy far outweighs most everyday cars, so much so I don't really use my car much anymore. I get 75mpg just running around town on the Burgman! Wife uses the car most of the time now. Even went to the NEC on the Burgman the other day, cruised at 70-75mph all the way, did 380 miles in total and it returned a genuine 78.9mpg for the entire trip. It was fun, and extremely comfortable into the bargain even though it rained most of the way. Incidentally, you don't actually get wet if you are doing more than 40mph as the air just goes over and around you on the scooter and the trip was non stop too. Here is a video clip of the Burgman 400 (standard model -not the one I have which is the Limited Edition). Just gives an insight into the size, comfort etc.

I'm currently part of a small team developing a new engine for motorcycles that will rock the world when it's released. The engine may also appear in at least one european car too. Talks still ongoing. Still about 1 year way from a preproduction fully tooled engine for bikes, and cars probably two years away. Fuel economy will be superb.

[logiclee]

More rpm is always going to cost you fuel. If you don't need the power of higher rpm then it's almost always better to be in a higher gear and lower rpm's.

I found it a bit silly in the article that they put the extra fuel consumption of higher speed down to higher rpm. Without mentioning the wind resistance at 90mph being over 3 times higher than at 60mph.

Yep agree. At motorway speeds aerodynamics is key to economy. The bluemotion Passat has taller gearing than my diesel Passat but I had one for a week and at 80mph ish there's hardly any difference in economy even though the revs are 500rpm lower. The Fabia really suffers economy wise above 70mph due to it's aerodynamics.

Cheers

Lee

[logiclee]

What??

Engines lean out on boost do they?? If they do they wont for long

Most forced cars run stoich ie 14.7/1 when off boost and richen up massively when on boost usually 12-12.5/1 at peak torque dropping into the 11's at peak rpm , some leaner , some richer but as a rough guide

Yep that's right but petrol air/fuel mixture is to become history.

The next biggest step in engine technology is just around the corner and that's friction ignition of petrol. There's already working examples using the exact principle of diesel ie no throttle, no spark plug and just adjust fueling for the power, ignition is done by compressional heat. It's done by very precise control of the valve timing and increases petrol efficiency by around 50%. The example given was for a 1.0 Focus power would be around 140bhp and economy of around 75mpg.

Expected to be in mainstream manufacture by the end of this decade.

Cheers

Lee

[Guest]

Lee, that's not new and there are so many problems to still overcome at the moment with that system. Now, due to new materials and better computers for cars there is renewed interest in this technology with hope of overcoming the many problems it throws up. There has been working examples that I've actually seen running even 9 years ago. Mitsubishi was as the forefront of this design but failed to implement it due to problems at that time that could not be over come, and moving instead to the very high compression petrol engine instead (14.1 compression which is about as high as you can realistically go for production cars with petrol without self destruction). Problem is (you prolly know this) when you put petrol under very high compression it increases the harmful particulate matter coming out of the exhaust, and to a level that makes diesel engines look like flower gardens. Those engines at the time simply put out too many harmful chemicals in the emmisions and the States banned them, so we got them all over here to kill us instead.

My team and I attended a conference in 'mainland Urop' about this very thing a couple of months ago but for the first time it does look promising that petrol friction ignition engines may come about. But it will be a long time ahead. One of the things that will if anything scupper it is the deadly emmisions that will still come from the exhaust...in particular, the particulates which will require a PPF (petrol particulate filter) that will need to be much more exacting in the way it works than the DPF on a diesel. Each particulate contains deadly chemicals that kills humans very quickly and the development teams are very worried about that aspect at the moment, and how to overcome it, obviously. The main problem being they cause Leukemia and lung cancer which develop quickly in humans exposed to the petrol particulates from an engine using high compression technology. Bigger compression ratios are still needed to make the friction ignition engines more efficient. I know we've spoken about it before but it's still reckoned that the next generation of diesel engines will provide the 100+ miles per gallon and emmision cleanliness that everyone is looking for. But these engines won't be out until post 2018 and will comply with all the current at the time EU regs and also be ready for the future regs too. Progress is well under way with their development I can assure you, in spite of what the manufacturers tell us and they are much less complex than the friction ignition engines. The other reason diesel will almost certainly rein supreme is the new types of fuel production that will be available in a decade or so. Diesels wont be burning stuff out the ground or grown on crops in fields. It's likely most will run on bacteria produced diesel fuel that will be almost limitless, won't take up valuable crop growing space, and absorbs twice as much CO2 during it's nurturing/growing than growing it on crops. And due to it's thermal efficiency, diesel will still produce less CO2 when it burns it's fuel over any given mile of travel than a new petrol engine, and that's what all the governments want.

The new modern small turbo'ed petrol engines are good but these are only a stop gap as has been made plain by some of the leading industry eggspurts, until the new super diesels arrive. I suspect petrol friction ignition engines will run alongside those for some time but only if the complication and emmission problems are overcome, and then they may take over on small engines. But it's very interesting stuff and can't wait to see what happens.

[DGW]

I've never found a/c to use any fuel, and it's best to run it as it's meant to be

The 2 fridges and chest freezer in my home similarly don't use any electricity to stay cold.

[Phil-E]

God that Vauxhall is rubbish on fuel!

We get mid 40 mpg from our car with 4 adults, full tank of fuel and a full (485 litre) boot, with aircon on and doing silly (100-120mph) speeds on the Autobahn.

Phil

[logiclee]

. But it's very interesting stuff and can't wait to see what happens.

Yep agree.

Major manufacturers are saying the next big advance is too far away for them to meet the C02 reductions in the next few years so many are concentrating on weight reduction.

In the meant time we have to wait for the new Petrol and Diesel Technology.

It's Delphi who have stated they have cracked the burning of petrol in a frictional ignition engine and they say they will not need additional filters.

This from their press release

Petrol engines will offer the same fuel economy as hybrids without the extra weight and cost. So say engineers at US technology company Delphi, who’ve worked out how to incorporate the direct-injection method of ignition used in diesels into petrol engines. And the potential benefit is staggering.

Harry Husted, Delphi’s chief engineer for advanced powertrain development, said: “The results of initial simulation work show this technology could improve engine efficiency by up to 50 per cent.”

In conventional petrol engines, a spark ignites the mixture of fuel and air. But in diesel engines, it’s the heat of compression that ignites the fuel and air mixture without the need for a spark. This allows the fuel to burn faster and more efficiently.

Until now, though, engineers have been unable to use the direct-injection method with petrol, because it’s too volatile to effectively control.

Delphi’s gasoline direct-injection compression ignition system overcomes this problem by using sophisticated valve timing, intake and exhaust tech to inject petrol in precisely controlled bursts. The company has successfully developed and tested a single-cylinder engine prototype and is already working on a more advanced system.

Husted added: “A multi-cylinder engine is being developed and will be ready to test later this year. It’s going to be a very torquey engine, with a similar feel to a diesel.”

And the new engine will have an immediate advantage over a diesel – and extra appeal to manufacturers: as unleaded fuel burns more cleanly than diesel, petrol engines don’t need an expensive and highly complex particulate filter. The new engine could be on sale by 2020

I think they must be using hydraulic valves instead of cam shafts as variable cams would not offer enough control

Cheers

Lee

Edited 11 June, 2012 by logiclee

[Guest]

Now that is interesting Lee. No PPF. It just might be they are using a lower compression than Mitsubishi were trying to use to gain more stability, and the bonus is fewer particulates. Mitsubishi also used a plenum chamber rather than direct injection, which although DI was possible at that time, was highly unstable for petrol. That, coupled with todays petrol which has almost no benzine in it is obviously helping alot and is making a difference I would warrant to the particulates. There is one other development company I'm aware of doing research and dev on this and they are attached to the car company we are in talks with about supplying an early version of our super diesel. It is the particulates giving everyone a headache and the EU's own report on particulates from petrol engines in city air makes grim reading and it is asserting that diesel engine particulates are less harmful and will continue to fall in the coming years, but the opposite for petrol engines will be true. Or maybe they need to look at a different approach to the whole compression petrol ignition issue. I do remember thinking at the time of the seminar that I would use a different approach to the one outlined to us. But then, it prolly wouldn't work at all...

We went over for talks and sat in on a key company development seminar with technical engineers telling us of there R & D plans for the next decade. For me it was like being in heaven. The friction/compression ignition petrol engine was discussed at some length but without too much technical detail as it's still highly secret, as is some of the work our team is doing on our engine. Time scales were not really talked about but we got the impression it's a very long way off. My colleagues did our bit with our presentation of our engine which seems to fit in really well with what the company requires. We then spent two days going around the factory watching engines being produced and tested, and getting the spec for engine plates ready for producing an engine they can bench test. Then we watched engines being rated for crankshaft bhp and torque, and a car being setup and tested for the euro mpg tests. Anyhoo, If we're successful, I'll be able to afford a new bigger scooter with more mirrors, flags and aerials!!! Thanks for that info Lee. What interesting time we live in! I love all this stuff.

[logiclee]

Not suprised that it's the US and Delphi that's pushing petrol technology as fuel costs are rising in the US and most Yanks have a fear of Diesel.

I'm usually involved with turbo charged spark engines with 20+cylinders.

http://www.clarke-en...-6-gas-engines/

http://www.youtube.com/watch?v=eXE1CUUx8T4

Don't work for Clarke's but for a company than runs it's equipment.

Cheers

Lee

Edited 11 June, 2012 by logiclee

[Kiwibacon]

when should air con be used? is it not to be used? will it be unlubricated if left unused? i am bursting hot, the windows need demisting, it will be unsafe.

I've found all my vehicles get their best fuel economy in the stinking heat. To the point where the best fuel economy I've ever had in two of my cars were at times when the air-con was running flat out.

It's essentially thinner air reducing aerodynamic drag enough to cover the losses of the AC.

[SlowBloke]

I am impressed with the ideas and information presented here!

I have noticed that my 1.6 diesel Fabia improves its furl consumption considerably once the outside air temperature rises. It was barely 50 in the winter but recently did 70 on a 20 mile trip in warm weather.

it's worth rembering a few basics regarding engine design. What worked for Dr Diesel still applies today. High compression ratio and combustion at the highest temperature and pressure stil give the best economy. This applies to all engines. Early jet engines (Whittle) had a CR of only 4:1 with very poor fuel consumption. Current jets are around 40:1 and new designs are aiming from 70:1. This is all in the search for better fuel consumption.

Diesel engines could go higher but the stresses and therefore cost of the engine increase as well so there is pressure to look for other ideas.

By the way, pre-combustion chambers were common in small diesel engines a few years ago. The engine runs more smoothly and can rev higher. But the economy drops by around 5%. This is why Ricardo developed the Comet engine (really the Comet piston). This has a bowl in the centre or to one side so that there is a sort of pre-combustion chamber but the flat top to the piston causes a lot of turbulence (squish and swirl) to improve combustion.

With petrol engines, the limit is the octane rating of the fuel. If you increase the CR. the petrol goes bang almost instantaneously. This is called detonation or more commonly pinking and is very bad for the engine. Diesel fuel is injected gradually so it has to burn quickly to avoid a similar detonation problem to pinking. If the petrol were injected like the diesel fuel, you could avoid this but the extra cost of the injection system would make the engine cost the same as a diesel.

Sorry if this is all ancient history but it might help put the pieces in place.

[raisbeck]

Nice bikes, but something like your Maxi-scooter goes to show how little Motor Cycles engines have moved on over the years as far as economy goes.

Only 223 kg in weight and only a little better in performance than modern 2 or 3 cylinder engine cars that weigh 3 times as much but can almost match the fuel economy with just a driver or maybe also a passanger..

george

Thats one of the reasons Honda has developed the NC700. Its half a Honda Jazz engine with a few tweaks resulting in a motorbike with high torque, low reving and over 80plus mpg. Same power output as typical 500 twin. Pure motorcyclists scoff at it but its not designed to ring out every ounce of power and rev its nuts off. I am seriously considering one. Bikes can be made more efficient, just up to now unless you want a C90 or an Innova there wasnt a whole lot of choice

Edited 14 June, 2012 by raisbeck

[Wilko251088]

Not suprised that it's the US and Delphi that's pushing petrol technology as fuel costs are rising in the US and most Yanks have a fear of Diesel.

I'm usually involved with turbo charged spark engines with 20+cylinders.

http://www.clarke-en...-6-gas-engines/

http://www.youtube.com/watch?v=eXE1CUUx8T4

Don't work for Clarke's but for a company than runs it's equipment.

Cheers

Lee

Is that a CHP engine? We use methane collected from waste water sludge digestion to power those. Think the ones we install are mainly Jenbacher :-p

[bluecar1]

the early indirect injection deisels in the 80's had swirl chambers (my old citroen bx19rd), they sooted the oil more than the direct injection rover montego's due to the fact the way the fuel burnt in the clyinder lead to uneven heating of the piston making it m=not quite perfectly round allowing more blowby (or that was the explaination at the time)

the IDI engines were quieter as the DI engines did not have as high injection pressurs as today and there was no multi-stage injection systems either as it was all rotary machanical injection pumps