Diesel or petrol?

[henk4]

A direct and specific comparison can only be made on equal terms. So, official MPG figures, although differing from real world conditions, can be seen comparatively for the relative consumption of engines.

whereby the excesses achievable with a petrol engine are far greater than with a diesel...

[lightweight]

whereby the excesses achievable with a petrol engine are far greater than with a diesel...

In absolute terms yes.

My understanding on the topic is that if two engines have a 20% difference in official manufacturer MPG, then this difference will more or less exist if driven hard. But the 20% consumption difference on 50 MPG is much smaller than the 15 MPG in terms of pump money!!

Any insights on this?

[LeonOfTheDead]

That's strange, are you saying that BMW has less than 15 years experience in producing (turbo) petrol engines? Apart from the 2002 they already had the 3.3 L in the mid seventies as well...sounds like a bit more than 15 years.
You are probably hinting at the fact that concerted technology development in diesel engines has produced such great results in a relatively short period of less than 15 years. (Common Rail 1998??).
And what would stop BMW from applying these VGT turbos and DI to the petrol car??

I mean with recent turbocharging application. Things changed a bit since the 2002. The 6 cylinders diesel engine received much more attention and updates or innovations in the last 15 years than their petrol counterpart which were somehow "ignored".

The reason why no one right now is adopting both DI and VGT in turbocharged petrol engines is because it isn't required by the market.
A quite simple engine as the new Fiat 1.4 unit, with just a modern turbo and good load of electronics, is sufficient to have everyone happy with the performance and the mileage. The same goes for the 3.0 twin turbo from BMW. It is already powerful and relatively frugal, adding more technology wouldn't justify an even higher price tag (people wouldn't justify it), and as everyone else would be doing the same, the result would have been once again a plain field, but using all at once all your updates instead of diluting them in another 15 years.
Everything is already present and usable, it isn't a sensible choice from a economical and marketing point of view though.
Porsche introduced the VGT in the 911 Turbo engine to keep the brand emissions down, and give a bit of hi-tech touch to a car that this time has little new to offer, especially if you think that the bump in power was limited compared to the outgoing 996.
So marketing once again.
It would have been a sensible choice to adopt them in the Panamera, but those engines come straight from the Cayenne, so an "older" project, but also from Audi.
Then there is the case of this "modern" technology not properly applied and resulting in a useless amount of money spent with zero results.
An example I already posted is the Renault 1.2 turbo engine in the Twingo GT (perhaps now updated), versus the 1.4 naturally aspirated unit in the Fiat 500.
The Fiat unit is nothing new, just a good old engine with a good tune.
The Renault engine has DI and turbocharging, still it manages/manage to achieve the same performance and a barely lower fuel consumption.

My point with diesel, elabprated talking with a teacher at University, is that diesel engines were used as a sort of "scapegoat".
With the state of the art of the pre-common rail era, diesels were unpopular, noisy and overwhelmingly performing. Only VAG with the 1.9 unit was showing some results, but it was a dead end as we would have later seen.
The point was developing "new" technologies and parts for petrol engines, commercialize them and leaving diesels alone, or give a spark of life (lol) to the diesel project, let it evolve until its limit, and then move back again on petrol transferring the technology meanwhile developed fir the oil burner.
This was you would have diluted the costs on two "products", rather than one only, and you would have used also the potential of the diesel.
Developing since the beginning the petrol engine would have killed the diesel since the beginning, as i would have been soon reached a point where petrol where simply better and "no one" would have bought a diesel again no matter how good it was.

So in the last 15 years or so, diesel received a lot of attentions and a lot of money was spent. A huge amount of result were achieved though, not only technically but also in cars sold. I don't think they didn't even expect such a success of citycars equipped with diesel engines.
No we reached a limit where power of diesel is increasing much slower than a couple of years ago, and only in larger engines (therefore higher consumptions and emissions) seem to be still gaining something (thinking of the recently updated Jaguar/PSA 3.0 V6).
Behind the 2.0 liter mark the diesel engine have a thinner margin on the petrol one, the power is generally the same if not lower, surely more torque (thanks to the turbocharcing), but the mileage isn't that lower especially if compared to larger diesel engines or even petrol engines of the same displacement. Still they cost at least 2.000 € more.

Not only the performance are now "stationary", but difficulties meeting the upcoming stricter emissions laws are raising (as foresee by the same automakers at least 5 years ago or more), while just adopting what has been developed for a diesel unit to a petrol engine gives back excellent result, at virtually very low costs, both in performance and emissions levels.
So right now, the petrol engine is showing bigger and simpler margins of improvements, and investments on it are being huge since some years.
Once again, not everything is applied all at once, since it isn't necessary to achieved the required results, and also to give some more years (about ten, we agreed) to the diesel units, so to enlarge even more the profits on that project.

This doesn't exclude a come back of the diesel engine in the future obviously.

It depends on the type of emission examined. For the same performance a Diesel emits less Carbon Dioxide, but more NOx.

Sure, still CO2 can be reduced on a petrol car, NOx not, in a diesel (and the urea based technology proved to be a sort of marketing failure).

That is correct, but it also applies to petrol engines. Porsche claim about 10 lt/100 km for the 3.8 Carrera. Floor it and you will see 3-4 times that figure.

A direct and specific comparison can only be made on equal terms. So, official MPG figures, although differing from real world conditions, can be seen comparatively for the relative consumption of engines.

I elaborated this in my previous post.
The main problem is that no one is going to drive slowly a 911 all the year, sooner or later, probably everyday, you're going to use all it's power.
On the other hand, diesel are generally driven more quietly.

whereby the excesses achievable with a petrol engine are far greater than with a diesel...

That's correct at the same time, but also the gain in performance is higher (once again thinking on similarly technologically equipped engines, just think of the 1.3 diesel and 1.4 petrol units from Fiat, both turbocharged and the petrol with no DI).

[Ferrer]

Damiano, the problem is, if you push a diesel and a petrol engine the fuel consumption in the petrol engine will increase much more dramatically than the diesel engine. You argue that diesels are usually driven more sedately but still, as I said you can't argue with 7l/100km at 180km/h.

[LeonOfTheDead]

Damiano, the problem is, if you push a diesel and a petrol engine the fuel consumption in the petrol engine will increase much more dramatically than the diesel engine. You argue that diesels are usually driven more sedately but still, as I said you can't argue with 7l/100km at 180km/h.

That correct, but have you driven a modern petrol engine at that speed?
I don't, and I would be very curious to know the figure it gives.
Surely I'm very happy with the mileage of the Stilo on the motorway, at 130-150 km/h it gives back 5 or 6 L/100 km at worst.

The point of my discussion is: we are know talking about top of the line diesel engines, at the apex of their development, and about still to be updated petrol engines, which just for a reason of marketing were relegated in the last years on a second level.

If it sounds like I'm saying "petrol is superior", that's not the tone I'd use, rather "petrol is easier to work with to achieve better results".
It was surely a sensible and smart idea to divide the development costs of the technologies on both engines, we all gained with that.

[Ferrer]

That correct, but have you driven a modern petrol engine at that speed?
I don't, and I would be very curious to know the figure it gives.
Surely I'm very happy with the mileage of the Stilo on the motorway, at 130-150 km/h it gives back 5 or 6 L/100 km at worst.

The point of my discussion is: we are know talking about top of the line diesel engines, at the apex of their development, and about still to be updated petrol engines, which just for a reason of marketing were relegated in the last years on a second level.

If it sounds like I'm saying "petrol is superior", that's not the tone I'd use, rather "petrol is easier to work with to achieve better results".
It was surely a sensible and smart idea to divide the development costs of the technologies on both engines, we all gained with that.

Actually I have. The little 1400cc under the Delta's bonnet is a gem, but at those sort of speeds it likes to drink. And especially if you find slower traffic in the left lane. Then it's going 120-180km/h in sixth, foot down all the way. And economy suffers greatly. Haven't done the math, if I can I'll do them this week, but I'd say that at least you'd be getting 9-10l/100km in Delta, if not more.

[lightweight]

The point of my discussion is: we are know talking about top of the line diesel engines, at the apex of their development, and about still to be updated petrol engines, which just for a reason of marketing were relegated in the last years on a second level.

From my point of view we are discussing what is available in the market. I would agree that petrol engines will benefit from a few technologies coming in the following years (HCCI, hydraulic valves) but such technologies are very expensive and still will not beat Diesels in MPG.

So the question is the price of the future engines relative to the MPG. That is a question that I am afraid no one in this forum can answer

I really think that the future of the petrol engine for urban applications is the [ame=http://en.wikipedia.org/wiki/DiesOtto]DiesOtto - Wikipedia, the free encyclopedia[/ame] engine presented back in 2007 by Mercedes-Benz. So there is no point in talking petrol vs Diesel as they could merge

Sure, still CO2 can be reduced on a petrol car, NOx not, in a diesel

As far as I know, Siemens is planning to introduce higher pressure piezo-injectors that will further reduce NOx.

[LeonOfTheDead]

From my point of view we are discussing what is available in the market. I would agree that petrol engines will benefit from a few technologies coming in the following years (HCCI, hydraulic valves) but such technologies are very expensive and still will not beat Diesels in MPG.

So the question is the price of the future engines relative to the MPG. That is a question that I am afraid no one in this forum can answer

I really think that the future of the petrol engine for urban applications is the DiesOtto - Wikipedia, the free encyclopedia engine presented back in 2007 by Mercedes-Benz. So there is no point in talking petrol vs Diesel as they could merge



As far as I know, Siemens is planning to introduce higher pressure piezo-injectors that will further reduce NOx.

HCCI and DiesOtto are, I think, still too far from the production line, and so seems to be hydraulic valves.
I'm ust considering VGT applied to (sequential) twin turbos laoyt matched to a DI system, on a petrol engine that is. Something that could be done tomorrow with no particular cost. And I think it would provide tremendous results.

[LeonOfTheDead]

Actually I have. The little 1400cc under the Delta's bonnet is a gem, but at those sort of speeds it likes to drink. And especially if you find slower traffic in the left lane. Then it's going 120-180km/h in sixth, foot down all the way. And economy suffers greatly. Haven't done the math, if I can I'll do them this week, but I'd say that at least you'd be getting 9-10l/100km in Delta, if not more.

The 1.4 is a gem, still lack a few updates, see the Alfa Romeo MiTo MultiAir.
BTW, with which engine are you achieving the 7 L/100 km?
Do you think the 1.3 diesel from Fiat, which barely achieve the 100 bhp mark, would give such figure at 180 km/h, provided you can reach that speed?

[john14]

I've only driven a petrol cars. Modern diesel cars are very impressive but I think many people still think diesel is bad due to the images that are stuck in the minds of many people. This image is of large 1970s diesel trucks. You would see so much nasty looking black smoke coming from those trucks and many people still willl only buy a petrol car because of the bad visual image they see when they think of diesel. Modern diesel cars and trucks are much cleaner and better for the environment but most people seem to ignore that.

[Ferrer]

The 1.4 is a gem, still lack a few updates, see the Alfa Romeo MiTo MultiAir.
BTW, with which engine are you achieving the 7 L/100 km?
Do you think the 1.3 diesel from Fiat, which barely achieve the 100 bhp mark, would give such figure at 180 km/h, provided you can reach that speed?

No I doubt the 1300cc diesel would do 7l/100km at 180km/h. Altough I doubt you can reach such as speed in it even downhill...

I was comparing the Delat to the 118d. Both have around 150bhp and both are hatchbacks that weight more or less the same. If we look at fuel consumption only, the diesel wins, no matter what speed you pick.

[LeonOfTheDead]

No I doubt the 1300cc diesel would do 7l/100km at 180km/h. Altough I doubt you can reach such as speed in it even downhill...

I was comparing the Delat to the 118d. Both have around 150bhp and both are hatchbacks that weight more or less the same. If we look at fuel consumption only, the diesel wins, no matter what speed you pick.

The 118d has also a larger engine though, which is something good at such speed.

[Ferrer]

Alright this afternoon I had a relatively long spirited (135km, 50km/h average) drive on local country roads and the trip computer says 11,6l/100km. The Bimmer would've been under 10l/100km comfortably in the same conditions.

We'll see how the full tank pans out in the Lancia.

[henk4]

Alright this afternoon I had a relatively long spirited (135km, 50km/h average) drive on local country roads and the trip computer says 11,6l/100km. The Bimmer would've been under 10l/100km comfortably in the same conditions.

We'll see how the full tank pans out in the Lancia.

spirited drives in a diesel will not require red line revving to get satisfactory forward movement. That 's where you gain in MPG. (problem that many people will call this type of driving not "spirited", because it lacks the emotion of a noisy engine)

[LeonOfTheDead]

spirited drives in a diesel will not require red line revving to get satisfactory forward movement. That 's where you gain in MPG. (problem that many people will call this type of driving not "spirited", because it lacks the emotion of a noisy engine)

but have more torque motivating your day, so it's not annoying at all.
I still prefer the simple turbo of the Stilo rather than the VGT of the Croma though.