Why do diesels have lower CO2 emissions than petrols?

[Uriel]

The concern for me with diesels is the nano diesel particulates. They still don't know what long term these have on health, but I bet in the future they will be found to be very dangerous.

<Cough!>

http://www.iarc.fr/en/media-centre/pr/2012/pdfs/pr213_E.pdf

The above seems to suggest that diesel fumes, in general, cause cancer in humans - but they just aren't sure which particular components.

I suppose you mean nano-particulates in particular, as opposed to diesel fumes in general?

 

[Haggisman]

That's for health reasons to increase air quality in London and not for environmental reasons

But ultimately it's not solving the problem, it's making it worse and moving it somewhere else...

 

[Dr Who]

Just FYI, you've referenced a 2 litre petrol against a 1.6 litre diesel....retard much

He referenced the performance of 2 cars with similar torque to demonstrate BHP is more important than torque.

Well done for failing to read. Bet you wish you hadn't made that retard comment now considering how hard it has now backfired

 

[Dr Who]

I thought the reason for diesels generally being steel engine blocks was to do with the much higher compression required so there was a requirement for the engines being stronger.

Not just compression, also the combustion forces.

Petrol engines usually use a cast crank and diesels usually use a forged crank, both are steel but the process makes the forged crank stronger.

Where alloy blocks are used in diesels they have steel liners and bolts that usually clamp the head to the crankshaft bearing caps to give the required overall strength.

Most don't bother and just use a cheaper cast iron block.

 

[miniyazz]

LOL

What?

Shame they don't levitate above the pot holes that they are not contributing to the repair of

If anyone else marketed a product as zero emission could you imagine the consequences.

Since pot holes are funded by general taxation and not vehicle excise duty, which they certainly contribute to by fuel tax even if they are benefit-scrounging lowlifes, which is unlikely, people driving Prius's and the like do in fact contribute to the repair of pot holes.

Cars are rather unusual compared to most products in that they actively emit waste gases. Therefore, given that it would be quite unusual to talk about the emissions generated by the production of e.g. a football, is it not reasonable to casually discuss CO2 etc emissions as those experienced by the consumer once the car has been purchased? It would be phenomenally difficult and in fact impossible to estimate the average emissions per km of a car including production emissions, given that no-one knows over what distance those production emissions would be averaged over. You're lucky they even give a g/km figure at all given the different ways in which a car can be driven.

 

[Jakus]

Basically just listening to a Diesel will tell you what the internals are putting up with, they are essentially exploding (detonating) the injected fuel as opposed to a petrol engine which is a rapid burn of the charge.

Stronger Pistons and Head gaskets are required, I'm not totally sure the rest need to be that much stronger as dynamic loads exceed combustion loads by a massive margin, It would obviously depend on how good the engine was before converting to diesel.

People keep mentioning Steel for blocks and liners, Steel is not used, Iron is used mainly for it's self lubricating quality.

 

[Jonnycoupe]

Self lubricating!?!

Irons used as it's cheap and robust . Bearing width is also a factor to deal with the loads.

 

[Jakus]

Self lubricating!?!

Irons used as it's cheap and robust . Bearing width is also a factor to deal with the loads.

Yup, graphite content rub a clean cloth against it.

Like I said combustion loads are not that big a deal maybe 25% so if you increased the torque by 50% your only adding 12.5% extra load to the assembly, It's the other 75% Dynamic load that were you double the RPM goes up by it's square. Revs break engines not power.

You may not find much about above on the net as with so many basic engineering and technical subjects sadly.

 

[Simon]

Yup, graphite content rub a clean cloth against it.

Like I said combustion loads are not that big a deal maybe 25% so if you increased the torque by 50% your only adding 12.5% extra load to the assembly, It's the other 75% Dynamic load that were you double the RPM goes up by it's square. Revs break engines not power.

You may not find much about above on the net as with so many basic engineering and technical subjects sadly.

The liners are still steel (or some other material like FRM).

BMEP is the issue with diesels (which is can be calculated from torque) so a 50% increase in peak torque increases BMEP by the same amout. The block needs to be stiff to stop it twistiing and distorting. A modern diesel running 17:1 compression ratio with 1 bar of boost burning a fuel that literally explodes puts a lot of strain on things.

The cranks and bearings are bigger due to higher cylinder pressures. Also pistons tend to be engineered with bigger ring lands to stop them cracking.

If revs are what kill engines, how is the S2000 fine with pencil rods and alloy block despite revving to 9000rpm

 

[Jonnycoupe]

Yup, graphite content rub a clean cloth against it.

Like I said combustion loads are not that big a deal maybe 25% so if you increased the torque by 50% your only adding 12.5% extra load to the assembly, It's the other 75% Dynamic load that were you double the RPM goes up by it's square. Revs break engines not power.

You may not find much about above on the net as with so many basic engineering and technical subjects sadly.

Rub a piston ring against it and see what happens.

But you won't be revving a diesel any more from increasing boost.... Just high BMEP and subsequent bearing load on the whole assembly. I'm struggling to see how you are citing Something like conrod robustness and tensile loading of the big end bearings as a reason why a Diesel engine is built stronger when it clearly has significantly lower mean piston speed.

I don't need a googlneering course.

 

[jono_astra]

.

 

[Jonnycoupe]

Turbo is a downsize enabler, not lean burn.

 

[jono_astra]

.

 

[adam cool dude]

I always thought the main reason diesel was lower co2 was because the whole combustion process is a lot more efficient which means less fuel is used and therefore less emissions. Petrol engines have gotten better with direct injection but now you have the coking problem to go with it.

A turbo shouldn't make a difference as you air fuel ratio should be the same.

 

[Jakus]

The liners are still steel (or some other material like FRM).
~

If revs are what kill engines, how is the S2000 fine with pencil rods and alloy block despite revving to 9000rpm

And why do you think they keep the reciprocating assembly as light as possible then ?

Rub a piston ring against it and see what happens.

But you won't be revving a diesel any more from increasing boost.... Just high BMEP and subsequent bearing load on the whole assembly. I'm struggling to see how you are citing Something like conrod robustness and tensile loading of the big end bearings as a reason why a Diesel engine is built stronger when it clearly has significantly lower mean piston speed.

I don't need a googlneering course.

I don't really understand what you said there
Thought you might have been able to figure out if your base (good solid petrol engine bottom end) is going to now operate at half of it's RPM range when you convert it to diesel it should be less stressed... was my point

If you start with a clean sheet heavier rods larger journals etc will surely help to damp down the nasty shock loads experienced with a diesel.
Pretty much the opposite would be best for high performance Petrol motor.

My original point was combustion induced Loads on the petrol reciprocating assembly are quite low, It should follow combustion induced loads as a diesel would be a higher overall percentage as the dynamic component is reduced because of the reduced RPM

To prove my point take a look at the Subaru Diesel in comparison to the Turbo petrol motor.

 

[Jakus]

yes it allows a smaller engine size and more power output to equal a bigger engines output but it also does really reduce the exhaust emissions too. Been on a lot of courses for why and how the new tech on cars works and why manufactures are doing these things and this is the reason why.

Forced induction motors (turbo/Supercharged) with the improved volumetric efficiency are going to give you more torque at lower rpm and like you say matching of bigger engine performance in a smaller lighter package which has lower parasitic losses than a larger motor.

 

[Gaygle]

<Cough!>

http://www.iarc.fr/en/media-centre/pr/2012/pdfs/pr213_E.pdf

The above seems to suggest that diesel fumes, in general, cause cancer in humans - but they just aren't sure which particular components.

I suppose you mean nano-particulates in particular, as opposed to diesel fumes in general?

Yeh the diesel particulates. Was reading a while ago they go deep into lung tissue and the human immune system can't even detect them.

 

[Haggisman]

It would be phenomenally difficult and in fact impossible to estimate the average emissions per km of a car including production emissions, given that no-one knows over what distance those production emissions would be averaged over. You're lucky they even give a g/km figure at all given the different ways in which a car can be driven.

Why not just put a similar "pollution tax" on the purchase cost of the car then? Based on the level of pollution generated by the production process?

There could even be a baseline set, where any car whose pollution levels from production are above a certain level incurs a tax, whereas those which are below are subsidised (using the generated tax) to make them cheaper.

If the aim of all these taxes is really to encourage people to be as green as possible, then surely that would be another step in the right direction?

 

[Simon]

Yeh the diesel particulates. Was reading a while ago they go deep into lung tissue and the human immune system can't even detect them.

Gasoline direst injection are likely to be even worse as the particles are even smaller. Euro 6 may see the introduction of particulate filters on gasolines.

 

[Simon]

And why do you think they keep the reciprocating assembly as light as possible then ?
.

For revs, which is the complete opposite of a diesel which is under much more load.

A high reving petrol needs has a BMEP of around 13, so the block doesnt need to be that strong but the reciprocating parts need to be built for higher internial loads from revs.

A modern diesel has a BMEP >20 so the loads are nearly twice as much, this is why you either go with a iron block or engineer a nice aluminum block which can cope with the design loads (just assume people won't remap). These loads directly act on the bearings which in turn trys to push the crank out of the block