Petrol or diesel?

[markjay]

Diesel engined cars can be made to be as refined and as quiet as petrol.

But it requires a huge amount of additional soundproofing and vibration damping, so this is only applied to high-end expensive models.

Run-of-the-mill Diesel cars will always be less refined than their petrol counterparts, even on new models.

 

[Deleted member 6183]

I don't know if it's a fact or not but I feel that petrol engines are lighter in weight than diesel resulting in a less 'nose heavy' drive.

Could be bollocks of course.

 

[Bellow]

I don't know if it's a fact or not but I feel that petrol engines are lighter in weight than diesel resulting in a less 'nose heavy' drive.
.

Petrols are invariably lighter than Brunelian constructed diesels. Petrols don't need such heavy transmissions either. Nor flywheels - to the benefit of throttle response (if it's a manual). Or such compliant engine mounts. All of which benefits handling.

 

[Piff]

I don't know if it's a fact or not but I feel that petrol engines are lighter in weight than diesel resulting in a less 'nose heavy' drive.

Could be bollocks of course.

Don't think it's bollocks - certainly not from say 20 years ago. I had a small loan car when mine was in for service - can't remember the make or model but it was a small hatchback with a diesel lump. I distinctly remember that slowing for a roundabout then wanting to steer left then right it wanted to go straight on due to the weight of the engine.
My take is that the low down torque of a turbo diesel is ideally mated to an auto box. We now have a petrol SLK (first petrol for many years) SWMBO uses it as her daily driver for typical 4 mile commutes. It does just under 30mpg on these runs (though I've had it at 36mpg on a dual carriageway cruise). Previous diesels used for this commute didn't suffer with DPF issues. If she used the E250 for these runs, because of the slower warm up time, it would be little better in mpg terms. Factor in the higher cost of derv in the UK and they both work out around the same.
So the E is used when we need more space and for longer runs

 

[GeeJayW]

Diesel engines have to mechanically stronger (higher combustion pressures, higher torque, bigger forces) than similarly sized petrol engines and are therefore typically heavier. An example is the cylinder block, cast aluminium has been used for petrol engines for decades. Whereas until quite recently, cast iron has been typical for Diesel engines.

The valve arrangements are essentially defined by factors like swirl number or tumble, which in turn influence combustion efficiency and emissions. If simple single-cam, simple valve train arrangements or integrated block-head designs gave benefits or reduced costs, guess what the manufacturers would be building?

Current common-rail direct-injection diesels are mechanically much quieter than equivalent diesels from say 15-20 years ago. There are just less parts thrashing about. By having electronically controlled multiple injections per cycle, they also have much reduced combustion noise than older Diesel engines. If gasoline engines go HCCI, combustion noise will be an issue.

Direct-injection gasoline engines are better at emissions (except particulates) than port injected engines and give some options about when and where the fuel is injected. Reducing intake/inlet valve deposits is more important for engines with port injection than it is for engines with direct injection.

 

[Bellow]

The valve arrangements are essentially defined by factors like swirl number or tumble, which in turn influence combustion efficiency and emissions. If simple single-cam, simple valve train arrangements or integrated block-head designs gave benefits or reduced costs, guess what the manufacturers would be building?

There would be a degree of retooling required (but there is with every new engine) but the air motion objectives for combustion need not be compromised.
My view is that car design is 'monkey see, monkey do' and that they all merely copy what everyone else does. Right down to cheating emissions tests. There hasn't been innovation in diesels engines since common rail arrived 20+ years ago. That they could have made more durable engines, cheaper to maintain for the operator - but either chose not to or it never occurred to them - is something they may rue. Had the diesel not the reputation of being an expensive engine to repair, then it may be in a stronger position to withstand the current backlash. A backlash to which the OEMs have no viable answer.

Reducing intake/inlet valve deposits is more important for engines with port injection than it is for engines with direct injection.

Why so, and which one is more troubled by deposits?

 

[GeeJayW]

The current backlash against diesel is about NOx emissions and the "need" to reduce congestion. It also serves to stimulate the demand for EVs which in turn encourages investments, job opportunities, growth in the associated industries. With this in mind (and it's been in view for years), who in their right mind is going to throw money into further Diesel engine innovation?

Inlet valve deposits have a greater effect on fuel transfer (port jection) into the cylinder than they do on air movement, especially at part load conditions where a full charge of air is not required. Hence for direc injection engines, inlet valve deposits are less of a worry unless they get very severe.

 

[Delderek]

Whatever the rights and wrongs, don't we all really know, that many more towns and cities are gonna jump on the band wagon and raise extra revenue by charging Diesels to enter.
This is probably just the start:

 

[Bellow]

The current backlash against diesel is about NOx emissions and the "need" to reduce congestion. It also serves to stimulate the demand for EVs which in turn encourages investments, job opportunities, growth in the associated industries. With this in mind (and it's been in view for years), who in their right mind is going to throw money into further Diesel engine innovation?

Agreed the NOx problem can't be easily fixed but it takes more than one nail to close the coffin.
Chicken and egg here. Diesel's problems are pushing the need for electrification but it isn't viable yet - and depending on residential circumstance, full EV may not be possible for many. Had VW not cheated and, diesels were less inclined to throw big bills at their owners, they could have survived longer and possibly a solution to the NOx problem could have been found. (It may still have to be, and there is a potential solution in 2T but the mindset is stuck where it is and diesel, 4T and 2T, is sullied in the minds of the public who may have fought harder for its survival were it cheaper to operate).

Inlet valve deposits have a greater effect on fuel transfer (port jection) into the cylinder than they do on air movement, especially at part load conditions where a full charge of air is not required. Hence for direc injection engines, inlet valve deposits are less of a worry unless they get very severe.

I think I need to brought up to speed here. My understanding is that port injection motors wash off the deposits (before they've formed) caused by PCV (the inlets on my (port inj) engine when opened up were clean) and that it is GDI lacking that washing action that is afflicted. Are (some/any/many) port inj affected by deposits and from PCV or fuel?

 

[Bellow]

Whatever the rights and wrongs, don't we all really know, that many more towns and cities are gonna jump on the band wagon and raise extra revenue by charging Diesels to enter.
This is probably just the start:

Diesel is still the staple for rural dwellers.

 

[fabes]

And that is where Parisian Meuser Macron got it so very, very wrong.

He (and many politicians) haven’t been to the country to understand the distances, the types of vehicle and the budgets many have to live off, leading to reliance on older lower tech diesels.
And despite them, air quality in the country is better than in the city….

A bit of a tangent, but a little vent (sorry…)


Back to the point, we bought a (3 year old) diesel back in 2014 (coming from a 2.2 petrol Zafira) a little due to the tax and mpg upside, but mainly because the n/a 1.6 and n/a 2.0 petrols of the car my wife wanted were carp – a really poor proposition. Manufacturers didn’t provide a viable alternative

Our 1.5dci QQ is the most popular (Renault) diesel in the world (even MB uses it), the internet tells me
It’s only an 8v (gasp) so torque builds lower and quicker (albeit ours is remapped) and will do 52mpg on a run, 5 up (or even 7 up) all day long.

A fair bit has gone wrong with it (little with the engine though, just brakes, tyres, drop links, even the washer pump) but it sounds like a Massey ferg until you’re on run. Its not pleasant any way you cut it.
It is low on revs and hence quiet on a run, but my 3.5l V6 is on less revs at 75mph (but only 10, perhaps 15 mpg down at that point)
Tomorrow we would replace it with a Turbo petrol

But in three years or so, a Petrol /EV self-charging hybrid that make the grade for a 7 seater will be what we want (no CVT though) Diesel will die just as it grew once the alternatives are available (imho)

PS Southampton are contemplating charging / banning diesel cars to improve air quality. Yet we all know it’s the Cruise ships idling on berth are the problem – but no one will invest in a to grid connection for them – (albeit it would need quite a bit of juice)

 

[GeeJayW]

Agreed the NOx problem can't be easily fixed but it takes more than one nail to close the coffin.
Chicken and egg here. Diesel's problems are pushing the need for electrification but it isn't viable yet - and depending on residential circumstance, full EV may not be possible for many. Had VW not cheated and, diesels were less inclined to throw big bills at their owners, they could have survived longer and possibly a solution to the NOx problem could have been found. (It may still have to be, and there is a potential solution in 2T but the mindset is stuck where it is and diesel, 4T and 2T, is sullied in the minds of the public who may have fought harder for its survival were it cheaper to operate).



I think I need to brought up to speed here. My understanding is that port injection motors wash off the deposits (before they've formed) caused by PCV (the inlets on my (port inj) engine when opened up were clean) and that it is GDI lacking that washing action that is afflicted. Are (some/any/many) port inj affected by deposits and from PCV or fuel?

If EVs can't pick up the slack left by the exit of diesel, hey presto reduced congestion (the real target).

When present in gasoline port injected engines, inlet valve (and port) deposits (formed from oil mist via PCV and potentially some fuel materials) absorb some of the fuel that was introduced by the injector. So less fuel goes into the cylinder than was asked for by the ECU. This can be especially interesting for transients. The airflow is pretty much unaffected especially if the engine is boosted. If the fuel used contained effective cleaning additives from the outset, then deposits don't form. This is termed keep-clean performance. In the U.K. pretty much all fuel provided by a 'proper' forecourt will provide some degree of keep-clean performance, though some fuels are better at thus than others.

If the deposits are already present, then using a fuel with more effective cleaning additives will remove the deposits over a couple of thousand miles (typically). This is clean-up performance. Again, some fuels are better at this than others.

With a direct injected engine, there are no fuel additives to clean away inlet valve deposits but as these don't have a huge effect on airflow (again especially with a boosted engine), their presence is something of an irrelevance.

 

[Crazyfool]

View attachment 84899 But, I really don't like the turbo diesel thing. I much prefer the smooth, endless acceleration of petrol.

I’m the same. Performance car wise I’ve had a 1.8T which was great, but the newer 2.0TDI’s at the time had the edge. The 2.0TFSI was much better, but unfortunately so unreliable. Then I replaced that for my first diesel, the E350 which is a fantastic engine, I still love driving it now, bit as I said previously, it’s missing something. The E400 on the other hand is something else! The 350 puts a smile on my face, but the 400 gives me the biggest grin.

 

[190]

It's been 15 years since I last had a petrol engine. I do recall that a noticeable difference for me when I first went petrol->diesel was that the in car noise at motorway cruise speeds was much less in a diesel, simply because the revs are so much lower than a petrol would be at an equivalent speed.

I guess noise insulation has changed a lot since then, so is this no longer a "thing" ?

One thing that's changed is that many petrol engines have acquired forced induction and the big increase in low rev torque has allowed them to pull much longer gearing. The 1.6 engine in my car is geared at 31.2 mph/1000RPM which is not far off diesel gearing.

 

[Bellow]

If EVs can't pick up the slack left by the exit of diesel, hey presto reduced congestion (the real target).

That, as a policy, the public are going to love!.....

When present in gasoline port injected engines, inlet valve (and port) deposits (formed from oil mist via PCV and potentially some fuel materials) absorb some of the fuel that was introduced by the injector. So less fuel goes into the cylinder than was asked for by the ECU. This can be especially interesting for transients. The airflow is pretty much unaffected especially if the engine is boosted. If the fuel used contained effective cleaning additives from the outset, then deposits don't form. This is termed keep-clean performance. In the U.K. pretty much all fuel provided by a 'proper' forecourt will provide some degree of keep-clean performance, though some fuels are better at thus than others.

If the deposits are already present, then using a fuel with more effective cleaning additives will remove the deposits over a couple of thousand miles (typically). This is clean-up performance. Again, some fuels are better at this than others.

With a direct injected engine, there are no fuel additives to clean away inlet valve deposits but as these don't have a huge effect on airflow (again especially with a boosted engine), their presence is something of an irrelevance.

Cheers. Makes perfect sense.