Petrol Vs Diesel

[davepoth]

Mr2Mike said:

That shows just how crap E85 "Gasohol" is compared to the proper stuff.

It's not the whole story. Ethanol increases the effective octane rating of the fuel, which allows more ignition advance and thereby more power from each ignition, more than overcoming the lower energy density of ethanol. You'll find that most cars that have power ratings for both petrol and ethanol (Koenigsegg is a good example) rate the ethanol higher than the petrol.

[Tiggstar]

MiseryStreak said:

DPF problems are totally model/engine dependent. There are no issues with the DPF on my Mazda 6 because it has the 2.2 but there are lots of issues with the 2.0 (Ford Mondeo) engine. Many of the issues arise due to not being replaced frequently enough and lots of short journeys where it doesn't get chance to clear and burn off particulates.

If it's your only car I would go for a petrol but only if it's a good one, no point suffering the worse fuel economy if it's a lacklustre eco stbox. There are some very good diesel engines now that are actually a better option for motorway driving, mpg aside. If you want to do any sort of track driving then a petrol is nearly always better.

Do you have a particular model of car in mind?

With my work being so close, it will only be short distance driving, residential roads then 10 minutes on the motorway per journey.

The two cars I've been looking at are BMW 118d 2.0 SE Coupe or Audi A3 1.6 TDi 105 3 Dr Hatch.. What do you think? They both have everything I'm looking for but read a lot of negative reviews the past few days about PDF's for short distance driving!

[Simpo Two]

davepoth said:

It's not the whole story. Ethanol increases the effective octane rating of the fuel, which allows more ignition advance and thereby more power from each ignition, more than overcoming the lower energy density of ethanol.

Isn't the simplest way to increase the octane rating to put more octane in it?

[Flibble]

Simpo Two said:

Isn't the simplest way to increase the octane rating to put more octane in it?

Oddly, no. Pure isooctane has an octane rating of 100, whereas many additives have octane ratings above 100. For instance ethanol is 108.6, and methane is 120.

[Flibble]

Tiggstar said:

The two cars I've been looking at are BMW 118d 2.0 SE Coupe or Audi A3 1.6 TDi 105 3 Dr Hatch.. What do you think? They both have everything I'm looking for but read a lot of negative reviews the past few days about PDF's for short distance driving!

For the price of the A3 1.6 TDI you could have the 1.4 TFSI COD which delivers 140 bhp and has a quoted 60 mpg. Tax band B too.

[menguin]

How much crude does it take to produce 1 litre of diesel - and the same question for petrol? Can we produce both diesel and petrol from the same crude oil, or would it be beneficial to produce only one type depending on how much of it we can obtain from the same quantity of crude?

[Flibble]

Depends on the crude oil; it's not all the same. Different fields produce lighter or heavier oils depending on the conditions when the oil formed. Lighter oils tend to favour producing light products such as diesel and petrol so you get more out of a litre of light crude than of heavier types.

As for diesel vs petrol; the oil is split into fractions via fractional distillation which produces both petrol and diesel (and a bunch of other stuff). Heavy fractions can be cracked to give light products, so you can crack diesel to give petrol and you can crack heavier fuel oils to give diesel. Thus the desired amount of diesel, petrol and other products can be tuned.

There's not really an advantage to using one fuel only, using diesel would waste the petrol fraction, and using petrol would mean converting diesel into petrol, which is more expensive than just leaving it as diesel. Producing a mixture is more efficient than single fuel.

[menguin]

Interesting, thanks!