Petrol v's Diesel

kravist

First post on the Green Issues Forum..so apologies if its all been covered before.

Basically, what i want to know is.......which type of engine produces a greater level of carbon emission...diesel or petrol?

(For example..take a 2 litre petrol/diesel engine.)

leeroybrown

I would suggest that that is a vastly over-simplified question.

In raw carbon from exhaust terms I would expect a modern diesel to produce less carbon emissions per mile but I wouldn't call that a good overall figure.

Capt'n Midnight

diesel is better than petrol , the best ones are roughly equilivant to a petrol hybrid but are far greener to manufacture than they hybrids

a diesel hybrid (peugeot next year ?) would be even better

petrol engines are lighter, cheaper and nippier than diesel - they are usually used when one of those three critera are important.

a steam engine with pistons is about 13% , I can't remember if this is single expansion or double . Trebble is usually only seen on static engines or large ship engines as the law of diminishing returns applies

very roughly a petrol engine is 25% efficient though they are getting a bit better, they are still worse than a diesel engine from the 1890's

diesel and steam turbine are about 40% , though nuclear power plants loose a few percent through heat exchanges

another clue
almost all commercial surface traffic over 5 tonnes that carries it's own fuel uses a diesel engine ships, trains, trucks, bulldozers, large standby generators

the other engine that is of a similar efficiency is the steam turbine, the differnence is that a steam turbine takes a long time to get up to speed and uses a lot of fuel in when idling, but since it's an external combustion will handle almost any fuel, hence they are used on ships and power stations

SeanW

Diesel is better IMO.

Not only are diesel engines singificantly more fuel efficient, but most give you the opportunity to use Biodiesel. If you want to go the whole hog, you can even convert some diesel engines to run on pure vegetable oil.

Also, in driving comforts, diesel offers two advantages, firstly, at low speeds (like stopping and starting in town traffic a <5 MPH) you won't have to use the accelerator as much because the engine tends to maintain a higher rev.

Diesels are also not as likely to break down in bad weather - with petrol if your spark plugs or points get wet as a result of driving through semi-flooded roads you're screwed.

leeroybrown

Another point to note here, even if it isn't a purely environmental point, is that the fractional distillation process used to process crude oil will by it's nature produce certain amounts of fuels falling into the 'petrol' and (broader) 'diesel' categories. It doubt that in the lifetime of fossil fuels that it will become an environmentally or economically viable argument for everyone to burn a specific variant just because it happens to produce marginally less carbon emissions at destination.

With diesel an efficient modern DPF would also be important.

On the point of heavy plant and machinery using diesel, it's not purely an efficiency argument. While the burn efficiency of diesel engines is attractive the power delivery characteristics with huge torque at low engine revolution speed is a compelling reason.

AngryHippie

I've been drivin an 05 avensis 2L d4d around lately, and If you stick to an 80 kmh limit, Its doing 60 mpg, and 45 at 120kmh on motorway. GO DIESEL

Capt'n Midnight

leeroybrown wrote: »

Another point to note here, even if it isn't a purely environmental point, is that the fractional distillation process used to process crude oil will by it's nature produce certain amounts of fuels falling into the 'petrol' and (broader) 'diesel' categories. It doubt that in the lifetime of fossil fuels that it will become an environmentally or economically viable argument for everyone to burn a specific variant just because it happens to produce marginally less carbon emissions at destination.

With diesel an efficient modern DPF would also be important.

IIRC most of the cracking and reforming is to produce petrol

On the point of heavy plant and machinery using diesel, it's not purely an efficiency argument. While the burn efficiency of diesel engines is attractive the power delivery characteristics with huge torque at low engine revolution speed is a compelling reason.

trucks gearboxes have a LOT of gears even with the high torque.
and once you get to large dump trucks and locomotive it's diesel-electric anyway



http://www.teslamotors.com/efficiency/well_to_wheel.php

look at the well to station figures

Lennoxschips

On the point of heavy plant and machinery using diesel, it's not purely an efficiency argument. While the burn efficiency of diesel engines is attractive the power delivery characteristics with huge torque at low engine revolution speed is a compelling reason.

Yep, I've driven loads of diesel cars (both for work and private) and only once drove a petrol car, and I was stalling the petrol car half the time, because I was so used to driving a diesel through the years.

To come back to the original question: Diesel is more fuel efficient than petrol, so has lower carbon emissions.

Petrol burns much cleaner than a diesel car with no filter (as are the vast majority), so if air quality is something you are concerned about then you might want to think twice about diesel.

If you want to reduce carbon emissions then it's not really a question of petrol vs diesel but using less fossil fuels full stop.

DublinWriter

Like for like, Diesel produces less harmful emissions plus takes a little less refining to produce than petrol.

kravist

leeroybrown wrote: »

I would suggest that that is a vastly over-simplified question.

In raw carbon from exhaust terms I would expect a modern diesel to produce less carbon emissions per mile but I wouldn't call that a good overall figure.

Firstly..thanks for the many responses.

This may very well be an over simplified question..but...for general effectiveness and influence on public attitudes..IMO thats exactly whats needed.

Simple solutions to simple environmental problems.


I acknowledge that use of public transport etc reduces carbon emissions more effectively..but where i live, it's not an option.


So...what i've decided to do..is crawl before i can walk...!

Off thread slighlty but here are the stepsd i've decided to take to try and reduce my carbon footprint

drive a diesel car/van...which can ultimatly be converted to biodiesel.

Plant some trees.

Burn firewood in a stove for heat.


When finances allow...get my wind turbine erected.



any more suggestions that wont cost an arm and a leg and are realistic?

DublinWriter

kravist wrote: »

drive a diesel car/van...which can ultimatly be converted to biodiesel.

I think that the eco-jury's still out regarding Biodiesel.

I've heard some interesting programmes on RTE Radio 1 stating that the production of bio-diesel is very, very harmful to the environment, but I'll need backup at this stage as the exact details escape me.

Lennoxschips

yeah, at the moment bio-diesel is being produced on land attained by slashing and burning rainforests, thus destroying habitats and releasing loads of stored carbon.

if burning rainforests isn't your thing then bio-diesel can be grown on agricultural land, competing with food crops and driving up the cost of basic food stuffs

SeanW

That's if you ignore the fact that there is a major surplus of agricultural capacity as schemes like CAP here in the EU and similar intervention and protectionist schemes in the U.S. will attest to.

There is also a slight difference between the problems being faced in Mexico - where the American obsession with the more wasteful and less useful biofuel of Ethanol has driven corn prices skyward - with biodiesel you can use much more stuff like recycled vegetable oil, jatropha weeds on plant fencing and marginal lands, as well as pure veggie oil.

EROEI (Energy Returned on Energy Invested) figures and most other metrics show biodiesel to be much more productive and kinder than the environment than bioethanol at virtually every stage of the production and usage cycle.

You will never hear me trumpeting how great Ethanol is because I don't believe it is.

Biodiesel - that's a different matter altogether.

Lennoxschips

The fact is that if Europe wants only 10% of it's fuel to be replaced by bio-diesel, more than 70% of Europe's agricultural land will be needed. The numbers just don't add up. So we let the third world grow the stuff for us, which involves clearing virgin rainforest.

Fossil fuels are essentially millions of years of stored biofuels. Every year we use up another million years or so of these stored biofuels. Unfortunately biofuel grown on the surface can't compete with our fossil fuel consumption.

One thing I agree with though, is that as long as we are using fossil fuels, we should supplement them with things like waste cooking oil, stuff we'd be throwing away otherwise.

DublinWriter

Lennoxschips wrote: »

Unfortunately biofuel grown on the surface can't compete with our fossil fuel consumption.

The issue that I was trying to remember last night was that growing the crops to produce biofuel seriously erodes top-soil. Top soil takes millions of years to produce.

saibhne

kravist wrote: »

First post on the Green Issues Forum..so apologies if its all been covered before.

Basically, what i want to know is.......which type of engine produces a greater level of carbon emission...diesel or petrol?

(For example..take a 2 litre petrol/diesel engine.)

Diesel actually has a higher CO2 emmission rate than petrol but because diesel engines run more efficiently would produce less CO2 on equal terms. However in practice you tend to have a much higher spec diesel engine to get the performance required. Check out this example where a 1 litre petrol car is equivalent in Co2 emmissins to a 1.4 Diesel

http://www.ecotravel.org.uk/fuels_5.html

so in making your choice, one thing to consider might be if you were buying a diesel make sure that you do not have a better (i.e. smaller engine) alternative that can do the same job in petrol.

Also from wikipedia.

Diesel-powered cars generally have a better fuel economy than equivalent gasoline engines and produce less greenhouse gas pollution. This greater fuel economy is due to the higher energy per-litre content of diesel fuel and also to the intrinsic efficiency of the diesel engine. While diesel's 15% higher density results in 15% higher greenhouse gas emissions per litre compared to gasoline,[3] the 20–40% better fuel economy achieved by modern diesel-engined automobiles offsets the higher-per-liter emissions of greenhouse gases, resulting in significantly lower carbon dioxide emissions per kilometre.[4][5]

Saruman

Hey i want one of those Tesla roadsters...
In the meantime i would settle for a diesel, especially if i could run off vegetable oil or biodiesel.

Capt'n Midnight

saibhne wrote: »

Diesel actually has a higher CO2 emmission rate than petrol but because diesel engines run more efficiently would produce less CO2 on equal terms.

petrol and diesel are both hydrocarbons, petrol has slighly more hydrogen and less carbon than diesel by weight.

from my previous post the picture on well to station efficiency also needs to be taken into account
81.75% Petrol - nearly 1/5 of the energy is lost before you get to the car
90.1% Diesel