Car - eco friendly fuel

phil140701

just to be awkward i thought i'd let you in on a little known fact
petrol-electric cars are the new darlings of the politically correct, but a two-year study conducted in the us suggests that they are more damaging to the enviroment than the landrovers and other 4x4s the green lobby hate.
CNW marketing research has published the results of its dust to dust survey , and it shows that when you include original production and the cost of recycling batteries and electric motors in the equation, hybrids fare badly.
CNWhas given to each of 312 cars a figure showing the energy cost per mile.
the industry average is us$2.281. but the fashionable hybrid toyota prius comes in well above that at $3.249. it's beaten by the petrol version of the land rover discovery at $2.525- not the most frugal land rover model.
CNW president art spinella says:"when broader issues such as enviromental impact of energy usage are taken in to account - the energy needed to plan, build ,sell , drive and disposal of a vehicle from concept to scrapping it - some high-economy vehicles actually cost society more than conventional or even large models over their lifetime".
more information on cnw's work can be found at https://www.cnwmr.com
TAKEN FROM MAY 06 ISSUE OF LANDROVER OWNER INTERNATIONAL MAGAZINE

RiffRaff

Ha,

If there's one thing this discussion proves it's that there's no ideal solution. I think the only thing we can conclude is that driving cars isn't environmentally friendly! We can't throw our cars away, we shouldn't necessarily convert them to LPG, hybrids are just as polluting (but in a different way) and a purely electric car will get us halfway to the shops before stopping and requiring a charge!

Maybe it's best just to do it the old fashioned way - use public transport where possible (not ideal for those of us commuting a long distance in a rural area) and try and minimise car journeys...

I'm just baffled that no one has come up with a better solution before now - apparently the first electric cars were produced by 1900 (according to Wikipedia anyway).

A useful website (but a slightly biased one) might be https://www.evuk.co.uk to find out more about electric cars - but I would take its articles with a pinch of salt...

RR

SusanCarter

gromituk wrote:

I don't think that is the full story though, because you need physics as well as chemistry! I don't know about the LPG situation, but diesel engines consume less fuel than petrol ones - and I presume produce less CO2 - because they have higher compression and thereby can extract more useful energy from the burning of the fuel.

Diesel engines consume less fuel because it is more dense. This means that the energy produced from one litre of diesel would be more than that from one litre of petrol which would be more than that produced from one litre of LPG. This is why diesel cars seem to have better fuel consumption figures.

This means that for a given amount of energy required for a vehicle, we would use a smaller volume of fuel if we used diesel. However, for the given amount of energy required (which would be the same regardless of which fuel was used), less carbon dioxide would be produced by the LPG.

As the carbon dioxide produced is the main problem in terms of pollution, I think this is probably more important than the "amount" of fuel used. Anyway, the "amount" of fuel used is difficult to compare as the longer the carbon chain, the more dense the fuel is.

gromituk

SusanCarter wrote:

Diesel engines consume less fuel because it is more dense.

Is that really the only reason? Doesn't the higher compression ratio of diesel engines make any difference at all? I would be extremely surprised if it didn't.

Sumostar

Hi
The higher compression ratio is needed to ignite the fuel. It squeezes the diesel until it ignites, so no need for spark plugs. That's why diesels are more reliable than petrol engines.

As for LPG, a conversion costs about £1000 - £1500 depending on what type you need. It is generally accepted that LPG is cleaner than petrol and diesel, and the beneficial tax rates make it cheap. It will be cheap for another 3 yaers at least.

As for bio diesel, I'm not sure that you need to convert anything. Some problems are caused by the greater viscosity of veg oil at low temperatures, but this can be overcome by thinning it. There are some good articles on the internet if you want to go to the trouble of producing your own!

gromituk

Sumostar wrote:

Hi
The higher compression ratio is needed to ignite the fuel.

That's true, but that's not the point. The higher compression ratio does indeed help:

"The higher compression ratio is helpful in raising efficiency..."

but as SusanCarter has said, the fuel is also more energy-dense:

"but diesel fuel also contains approximately 10-20% more energy per unit volume than gasoline."

From http://en.wikipedia.org/wiki/Diesel_Engine.

gromituk

Beverley wrote:

Feeling defensive here.

Sorry - you stuck your head above the parapet! My comments about excessive car usage are general.

phil140701

i have just found the perfect car its tax exempt ,probably mot exempt and runs on batterys its a range rover thats been converted to batterys email adress available for more info oh and its only £750

SusanCarter

gromituk wrote:

Is that really the only reason? Doesn't the higher compression ratio of diesel engines make any difference at all? I would be extremely surprised if it didn't.

Now you point it out, I've realised that I am only considering the fuel and not energy efficiency of different engines.

If LPG produced half the carbon dioxide per unit of energy but the engine was half as efficient as a diesel engine in harnessing the energy then they would work out the same. I guess you would need to know the efficiency of a given vehicle and factor it in.

If the manufacturer gives a figure for fuel consumption (or I suppose you could work it out from your actual usage of a vehicle) then perhaps you could calculate the carbon dioxide produced per mile driven.

Having said that, why is diesel more efficient? Is it that it has a low percentage of unspent fuel or is it to do with the conversion of the energy from the explosion inside the engine to the movement of the car? My husband's van runs on either LPG or petrol so for these two I would guess the only difference between their efficiency would have to be unspent fuel but of course Diesel engines work by compression so maybe that is where the difference in efficiency comes from? Any unspent fuel coming out of the exhaust would then have to be factored in using the CO2 equivilent.

Any answers?

gromituk

It is more efficient in terms of recovery of useful energy because of the conversion from the fuel burning to movement of the car. This is because the change in pressure as the piston moves is greater, leading to more energy being extracted as mechanical power rather than being wasted as hotter exhaust gases. Unspent fuel is a factor, though a minor one which is more important when considering emissions of "traditional" pollutants rather than CO2.