The end of diesel cars is coming soon!


#21

To be fair to Mazda, there has been a huge amount of money and time invested in regular petrol engines, and relatively nothing in the Wankel - so the reliability difference is not surprising. The main issue for me is how they really expected to sell any, given these issues (and the comedy fuel consumption), and why they thought they could get away with foisting such a car onto the public.

That said, it’s not a stupid choice if you want a fast fairly large car that’s only 3-4 years old for a couple of grand, and can cope with 100% depreciation in a rather short time!


#22

A few years back I bought an 08 for £2.2k with 20k miles and ragged it around for a little over a year whilst someone else was paying for the petrol. Sold it with 40k miles on for £1.9k.


#23

#24

They did spend a lot of time on the Wankel but there are three fundamental problems.
The gas seal is a rectangle, so impossible to make tolerant of machining variations and wear.
The combustion chamber, at the time the spark plug fires, is the shape of a bit of banana peel, so the flame path length from plug to edges varies massively in each direction, so very poor combustion.
It does depend on the geometric detail but no practical engine has been made where the rotor tip speed doesn’t exceed the flame path speed in the running rpm range (it is about 3,500 rpm in the Mazda). That means that any fuel/air mixture upstream of the spark plug is moving away from the flame faster than the flame can burn it above that rpm. Adding a second plug which fires after the main one helps a bit, but basically at moderately high revs quite a lot of the fuel ends up burning in the exhaust pipe serving no useful purpose.
I think it would have been possible to reject the engine as a poor solution at the R&D stage if it wasn’t for irrational enthusiasm and marketing.


#25

Rob’ll be gutted…


#26

That’s a very useful general purpose phrase. I’ll file it away if that’s OK with you.

VB


#27

BMW 320D, but it does 55mpg.


#28

A Deltic is what you need, pistons everywhere, 3 cranks and a gear train to please the eye of a watchmaker:)

Used on trains and converted for naval use as a gen set as well as main propulsion in the old Ton Class minesweepers (mainly Al alloy so low mag sig), luverly things.


#29

…and Stu’s Astra. :slight_smile:


#30

Not really, my pint is half full :slight_smile:.


#31

One of my favourites was the BRM H16 engine. Only 3.0 Litre and 16 cylinders.


#32

Yes, it was effectively 2 of the previous year’s V-8 1.5 litre engines flattened with their cranks geared together.
They used to break these gears a lot though. The 2 engines never had identical resonances and when one was going into resonance and the other wasn’t the loads in the joining gears was huge. It was OK if the rpm was passed through quickly accelerating through the gears but if the driver held it near there going round a corner - bang!
The Napier Sabre H24 aero engine had a system of helical/straight floating gears joining the cranks which shuttled back and forth if one crank was resonating more than the other, so it didn’t have that problem, though they were fiendishly complicated to work on (they are sleeve valve too) and had a more frequent service interval than the Merlin.
I used to frequently drool over the cutaway engine displayed in the aeronautical section of the Science Museum whilst I was a student.

Animations showing the sleeve valves and the helical/straight transfer gears:-

http://www.hawkertempest.se/index.php/contributions/photos/329-napier-sabre-animations-created-by-sergio-pasquali


#33

Amazing 3D animations :+1:


#34

No t worth having a diesel over here. The fuel purchase is cheap, but the NZ gubmint charge you $0.058 for every kilometre you drive. Doesn’t sound like much, but if you’re getting 15km from a litre of diesel - that’s about 42mpg - then you’re effectively paying nearly an extra $0.90 for your litre of diesel. Which makes it quite a bit more expensive than petrol.
And the annual registration cost for a diesel-engined car is more expensive than the same petrol-engined model.

Dunno what your fuel prices a rein the UK now, but I suspect you’re facing similar issues.


#35

My local Sainsbury’s is £1.09.9 per litre for petrol and diesel.


#36

Getting closer…


#37

Can’t come too soon


#38

Just bought a diesel car, picking it up on Sunday.

Tax £20
Local authority parking permit half price because of the emissions.

Win Win so far!


#39

Oh the irony!


#40

Isn’t/ wasn’t there a supercar with a W configuration engine. Seem to recall VW were involved?
I recall when Audi were having great success with the 4WD Quattro in rallying that VW had a Scirocco with two engines which they were trying to develop as a competitor.