http://www.guardian.co.uk/uk/2013/jan/27/diesel-engine-fumes-worse-petrol
CityCyclingEdinburgh Forum » Debate!
"Diesel fumes more damaging to health than petrol engines"
(10 posts)-
Posted 12 years ago #
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This is not really news, but definitely worth pointing out again.
Also, from earlier in the year Diesel exhausts do cause cancer, says WHO.
Posted 12 years ago # -
Yes, but isn't it surprising that derv which costs more, is dirtier, and produces more carcinogenic particulants, is so popular and seems ever increasingly so. It also has a much lower freezing point making it more difficult to start your motor in very cold conditions. Counter-intuitive I always thought, perhaps it is that "it costs more therefore is better" mentality. Performance is not as good either in deisel engines. Ho hum.
Posted 12 years ago # -
It is more popular in cars because it has a higher energy density so you get a better mpg, which mostly offsets the extra cost of the fuel. Its more popular for other stuff because the engines produce much more torque meaning heavy stuff can be moved.
Its dirty because its thicker coming out at a lower part of distillation cut, it contains more carbon and other impurities which are effectively boiled out in gas and petrol.
Because it comes out at a lower point in the distillation it is much thicker, the thinner lighter material boils off, freezing point is irrelevant for cars in the UK. The issue is that when it gets cold it gets even thicker and if the viscosity drops the ability to pump the stuff to engine becomes an issue. It becomes harder to start because diesel engines need to warm the fuel before the compression cycle to get the engine to work optimally.
Its unlikely to become more popular in Europe as its cost is only going up due to Europe having to import more of it from further and further away. Enormous oil refineries are set up in the middle east to sell us diesel and the US petrol. A large proportion of the petrol refined in Europe also goes to the US.
Posted 12 years ago # -
The issue is that when it gets cold it gets even thicker and if the viscosity drops the ability to pump the stuff to engine becomes an issue
My old boss found this out to his cost trying to drive from Peebles to Edinburgh after a -17 temperature overnight. Killed the fuel filters and pump in his wife's lovely new Landcruiser trying, then proceeded to do the same in his Freelander.
Posted 12 years ago # -
@steveo
Its more popular for other stuff because the engines produce much more torque meaning heavy stuff can be moved.
Does this mean that you can move your entire household contents in a diesel Corsa but not in a petrol Corsa...I would have thought in this case torque was irrelevant to size and therefore just how much you can shoehorn in.
Or does it mean that you can get your six burly mates around town faster and better?
Posted 12 years ago # -
More torque at lower revs also = easier to drive because they are harder to stall.
I think it was air pollution which was responsible for all the chest infections I used to get when I did intervals around Arthur's Seat on my way home from work.
Posted 12 years ago # -
Lowers the embarrassment factor then, being harder to stall, now why did I not know that!!? So important in this day and age, not getting a red face!!
Easier for learner drivers too, being harder to stall at lower revs. Who would have thought it :-P
Posted 12 years ago # -
In a small car it means that you can carry more stuff with less stress on the motor. But they're generally in Clio's and other such cars because you increase fuel efficiency by about 30% which actually is a "good thing".
But where deisel engines are really useful is in big units like buses. A routemaster bus produces about 100 bph much like my car the difference is that it can produce that at 100rpm whilst my engine would be doing 20x that. Basically the bus can move 15 tonnes from a standing start whilst mine wouldn't be able to move it at all unless something else were to get it up to a speed that the petrol engine could function.
Think of it like this. Uberuce and Kaputnik can both get up Arthurs seat at the same speed, Uberuce will doing at 5 rpm with a 80" fixed gear. Kaputnik will be down in a more sensible gear doing 70 rpm. If for some reason they stopped half way up, Uberuce would have much less trouble getting started because his optimal cadence is only just lower than his starting, whilst Kaputik would have have strain himself working at a cadence he was not comfortable in until he could accelerate to a good working speed.
The fuel in this case is actually irrelevant its the design of the engine. Rudolf Diesel's engine is very clever and can basically "burn" anything that can be pumped to the cylinders. Due to the way it works it doesn't rely on being moving to operate optimally.
Posted 12 years ago # -
[diesel] is more popular in cars because it has a higher energy density [than petrol]
Small technical point:
Diesel has a similar energy density to petrol. The fact that diesel engines are more efficient than petrols is due to the fact that you can have a higher compression ratio in a diesel (typically 22:1 against 12:1). Basically more bang for your buck.
Petrol engines suffer from pre-ignition (knocking) if the compression ratio is set too high. However, recent strides have ben made in increasing the efficiency of petrols by increasing the compression ratio using clever techniques like direct injection of fuel.
An example would be the 74mpg petrol Fiat 500 0.9 TwinAir. More here:
http://eandt.theiet.org/magazine/2013/01/how-to-100mpg.cfmPosted 12 years ago #
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