[RJ555]

Many years ago there was a scarcely released VW Lupo that "apparently" received 92-99mpg. There are of course cars like the new Kia Rio claiming 88mpg (which seems the highest of current cars in the UK) as well as electrics (the sky high 120+mpg advertised by the Ampera) and hybrids of course.

Most cars however seem to be stuck in a more conservative 50-60mpg range. Obviously weight must be a factor, but there seem to be plenty of diesel superminis struggling to break these barriers.

What exactly is holding the majority of diesel cars back, or is it more the case of false advertisement at the higher end of the spectrum?

[2_plus_X_equal_me]

Arabs pay in sand to companies to hold back cars MPG/


TROLOLOL

[2_plus_X_equal_me]

First reason


Now on a serious note. Its all about the economy and fuel prices etc. Low fuel prices during the 80s/90s gave customers the green light to purchase big 4x4 and other vehicles drunk on fuel.

It was only when fuel prices increased did major companies shift their attention into creating vehicles that had good mpg ratings etc, as most individuals could not afford to fill up vehicles that had poor mpg rating.



Second reason.

New rules being past interns of safety means more safety gear for for vehicles. So the heavier the car the lower the mpg will be. This was not a problem in the past.


Hope i helped you with your homework

[gbduo]

Yeh weight, people want safety and luxuries like air conditioning which is heavy and uses fuel thus reducing mpg. But if you don't use the A/C you screw the system up. So if you want a uber economical car, you buy one of these with 60ish mpg, strip it out, insert roll cage and light weight seats, no creature comforts and go.

The Aygo is a bit like this, but its still too lardy.

[JC.]

I wouldn't worry about it, so long as you're comfortable thats more important than bean counting.

[viksta1000]

the government doesn't subsidise production of green cars as much as they should, because they know if the technology were to progress to a stage where hybrid/electric/high-mpg vehicles were affordable, demand for fuel would reduce taking along with the the stupendous amount of government tax revenue it generates

[CurlyBen]

There's a limit to the efficiency of a thermal engine (Carnot cycle if you're interested) and we've got quite a long way towards that limit, so you see diminishing returns - you need to put in more and more effort to see smaller and smaller gains. The next big change will be when KERS becomes useful, or some other technology comes along (Dies-Otto perhaps). Simply refining engines won't do much more.

[Friggerpants]

I rememer reading about a 6 stroke cycle engine, which would be very efficent (Inject water to cool clyinder, free power stroke). However I think it may have just been theoretical.

I reckon it'll go the way of diesel-electric..........Little diesel generator, powering batteries and electric motors!

[Dan1909]

(Original post by Friggerpants)

I reckon it'll go the way of diesel-electric..........Little diesel generator, powering batteries and electric motors!

That won't happen, as it would be more efficient to just use the generator to power the wheels, and not having the efficiency losses involved in generating the electricity, storing it, losing it again in the motor.

Which is what we have - we call them engines

[Ice Constricter]

(Original post by viksta1000)
the government doesn't subsidise production of green cars as much as they should, because they know if the technology were to progress to a stage where hybrid/electric/high-mpg vehicles were affordable, demand for fuel would reduce taking along with the the stupendous amount of government tax revenue it generates

Thissss.

[Dan1909]

(Original post by viksta1000)
the government doesn't subsidise production of green cars as much as they should, because they know if the technology were to progress to a stage where hybrid/electric/high-mpg vehicles were affordable, demand for fuel would reduce taking along with the the stupendous amount of government tax revenue it generates

(Original post by Ice Constricter)
Thissss.

While partly true, it won't hold out like that for long. Once electric vehicles start to appear in numbers that actually make a dent in the tax levels being brought in from fuel the government will just introduce new taxes to tax the electricity used by electric vehicles, or they'll simply stick a massive road tax figure on them which is around the level that they would pay in fuel tax each year.

The change to EVs is one that 100% will happen at some point, and the government will be sure to adapt to ensure they continue to get tax from them, they cannot afford not to.

[CurlyBen]

(Original post by Friggerpants)
I rememer reading about a 6 stroke cycle engine, which would be very efficent (Inject water to cool clyinder, free power stroke). However I think it may have just been theoretical.

I reckon it'll go the way of diesel-electric..........Little diesel generator, powering batteries and electric motors!

Crower engines. Run experimentally, but use at least as much water as fuel. I think there were also issues with acid formation when the water mixed with exhaust gases and with uneven cooling of the block, not to mention corrosion. Thinking of getting free energy from waste heat, some clever bugger realised that the Merlin engine in the Spitfire was pumping out a lot of heat through the rad, so he made a special duct with the radiator sat in the middle of it. This acted like a miniature jet engine and was worth several HP, I think it put about 10kn on the top speed compared to normally cooled engines!

(Original post by Dan1909)
That won't happen, as it would be more efficient to just use the generator to power the wheels, and not having the efficiency losses involved in generating the electricity, storing it, losing it again in the motor.

Which is what we have - we call them engines

Erm.. diesel electric trains! The advantage is you can run the engine at it's most efficient speed all the time and don't have to use gearboxes etc. Downsides are they take up a lot of space and work best when the engine's running at it's peak efficiency, which will be something like 80-90% of rated power output. Cars use maybe 15-25% of their power to cruise, so aren't at or near their peak efficiency speed.

[Manitude]

There's going to be a maximum value somewhere, there's a limit to how hot a combustion engine can realistically get while being safely within a car. There's a maximum efficiency of the engine, and a maximum amount of energy that can be extracted from the fuel by chemical reaction, so there's a limiting factor there. Though the design of the engine is what seems to be holding us back. The Diesel engine is pretty efficient, but not THE most efficient engine theoretically possible (i.e. Carnot engine). Unfortunately the Carnot engine appears to be impossible to build.

[gbduo]

We have 53% efficient diesel engines on board ship, however this is achieved largely because we are diesel electric and running at constant load for days and we have massive heat recovery plants and turn water into steam to heat stuff round the ship.

I think you would be going some to get a car engine to be 35% efficient. Shocking really that 65% of the fuel you burn is just heat and noise (and technically light). Ah well, such is life.

[edd360]

Why are we still so ignorant as a species?

[Kevmeister]

(Original post by CurlyBen)
There's a limit to the efficiency of a thermal engine (Carnot cycle if you're interested) and we've got quite a long way towards that limit, so you see diminishing returns - you need to put in more and more effort to see smaller and smaller gains. The next big change will be when KERS becomes useful, or some other technology comes along (Dies-Otto perhaps). Simply refining engines won't do much more.

Ferrari and Porsche are working on KERS based hybrids, so that technology will filter down to other cars in the VAG and Fiat groups, but not for another decade or so.

In the near future, I think Ford's 1.0l eco-boost engine mated to a small hybrid is the way forward.

Aerodynamics and weight are key to higher mpg.

[gbduo]

(Original post by Kevmeister)
Ferrari and Porsche are working on KERS based hybrids, so that technology will filter down to other cars in the VAG and Fiat groups, but not for another decade or so.

In the near future, I think Ford's 1.0l eco-boost engine mated to a small hybrid is the way forward.

Aerodynamics and weight are key to higher mpg.

I think Porsche are using the Williams F1 KERS technology with the flywheel design? I saw a programme on it on Megafactories or something on Discovery. Very interesting as it is a British design! Woohoo!

[Kevmeister]

(Original post by gbduo)
I think Porsche are using the Williams F1 KERS technology with the flywheel design? I saw a programme on it on Megafactories or something on Discovery. Very interesting as it is a British design! Woohoo!

I know its a flywheel design, can't remember if its Williams or not - I read a 'first drive' report a few months ago now. They want to refine the system and reduce it's size/weight. Porsche seem to be using the system instead of increasing capacity/using blown engines, to enhance performance.

Ferrari's one is mooted for the next Enzo. That'll be interesting.

[walterwhite123]

(Original post by Dan1909)
While partly true, it won't hold out like that for long. Once electric vehicles start to appear in numbers that actually make a dent in the tax levels being brought in from fuel the government will just introduce new taxes to tax the electricity used by electric vehicles, or they'll simply stick a massive road tax figure on them which is around the level that they would pay in fuel tax each year.

The change to EVs is one that 100% will happen at some point, and the government will be sure to adapt to ensure they continue to get tax from them, they cannot afford not to.

It won't happen. EV's are impractical for huge swathes of the population.

[Dan1909]

(Original post by walterwhite123)
It won't happen. EV's are impractical for huge swathes of the population.

It WILL happen.

Once fossil fuels run out, we will need an alternative. So far, unless somebody invents a technology that we've not even thought of so far, then we will be using EVs.

And by that point, the technology will have reached a point where they're not impractical at all. While they are now, they won't be in 20+ years time.