Thanks Pete, thats me and maybe a few others educated on the subject.
Mal.
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Latest diesel engines seek to quieten the clatter by injecting a 'pilot' shot of diesel before the main charge. Generally it's easy to tell the difference between simple,cheap(?),noisy engines and later complex,expensive,quiet(?) engines. For a really good example of a really noisy engine have a listen to a diesel Maestro (van, car uses different injectors which makes it quieter) or Sherpa/freight rover then listen to something like a BMW/V70 Volvo (I think it's the V70). Just for the record the Maestro diesel engine (Perkin Prima) was a record holder in it's time for fuel efficiency and so I guess noise level wasn't a priority when it was designed.
Steve.
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On the subject of diesel noise I used to own a 1.8 1988 diesel Galant and it was very quiet compared to many diesels at the time and a lot I'v heard since!.
Mal.
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Without wishing to go off-thread: I'm curious, why do taxi drivers keep their engines (especially diesel) running endlessly while waiting on the rank?
Avoid the need to re-start and drain the battery?
Keep the car warm?
Other reason?
Oz (as was)
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Mal,
My boss owned a diesel Colt Lancer something or other (square styled estate!), I don't know what he did to it but it needed a new engine at 12k, still running but had no power and gobbling fuel. The dealer/importer paid for it but he had to wait months to get it fixed.
Steve.
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Might be the same silly reason why many a diesel owner leaves his car outside a newsagents with the engine running, but without the risk of getting it nicked or slipping into gear and going off without the driver.
Mal.
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Keep the car warm. It goes very cold inside in about 10 minutes flat.[1]
In the summer we turn the engine off and push the car forward 20ft every time the guy at the front gets a pick up.[2]
[1] The latest specialist cabs, ie 7-seat Fiat and Citroen vans with windows, come with "standby heaters".
[2] Very few cabs have aircon, and even if you have got it some passengers will get in and open a window!
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Just for the record the Maestro diesel engine (Perkins Prima) was a record holder in it's time for fuel efficiency and so I guess noise level wasn't a priority when it was designed.
Quite correct, Steve. The Perkins Prima was the first 'direct injection' car engine, i.e. with the fuel injected directly into a combustion chamber bowl formed in the crown of the piston, and the emphasis was on fuel efficiency and high power (for its time). 100 mph and 100 mpg was claimed for the diesel Montego, and this was achievable (though not both at the same time of course!).
The car version had two-stage injectors, i.e. the needle lifted part-way and was then momentarily checked by a spring before lifting fully. This stepped injection slowed the combustion rate slightly to make less noise.
Previous diesel car engines were all 'indirect injection'. In these, the fuel is injected into a pre-combustion chamber (pcc) in the side of the cylinder head. The pcc is connected to the main combustion chamber by a passage. There isn't enough air in the pcc for full combustion so the fuel only starts to burn there and, as the burning mixture expands, it pushes along the passage into the main combustion chamber where there is sufficient air to complete the combustion. This makes for a relatively slow burn whereas the direct injection engine has a very fast burn because there is always enough air available.
The main advantage of the indirect injection engine is that it is less noisy and produces less NOx, both due to the slower burn. The big disadvantage is inefficiency due to pumping losses (i.e. the power lost in pumping the burning air/fuel mixture through the passage) and high thermal transfer (i.e. heat transfer from the pcc and passage into the cylinder head and hence into the cooling system). This inefficiency consumes fuel and wastes energy in the form of heat loss, hence the engine is not so economical.
With the Prima, some of the noise was also due to the car/van body construction and engine mounting arrangements and I don't believe diesel engines were in mind when it was originally designed. Modern diesel cars have a more rigid construction and better noise insulation. Some, like the Rover 75, have a double bulkhead between the engine and passenger compartments.
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Just to be annoyingly pedantic, I think the Fiat Croma had a direct injection diesel before the Montego/Maestro, at least in a passenger car, although it wasn't sold in the UK.]
Sad, aren't I?
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So why is my Octavia SDi (direct injection, I believe) so much quieter than any other (direct- or indirect-injection) diesel engined vehicle I've owned or driven? (Vectra DTi, Pug 405, Mondeo, Montego estate, Maestro van, Transit)
I mean the noise the engine makes, even with the bonnet up, as opposed to the noise heard inside the car.
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Dizzy,
Am I right in thinking that different injectors are used in the vans compared to the cars? I'm sure this is what my brother tells me (he runs both), he's also commented how much more the 2 stage injectors cost to have reconditioned. The tone of both engines is very different, the van sounding 'hard/harsh' whereas the car has a more subdued rattle.
DTD. I
Is the engine in your Octavia a PD diesel, if so this could account for the different sound and noise level. My brother-in-law runs a Golf TDi SE (100 bhp, I think), this makes a really strange sort of sound when he puts his foot down, but the fuel economy is great, until he puts his foot down!
Steve.
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DavidHM, you are not being pedantic. Perkins were way ahead of FIAT but some politics delayed the launch of the car fitted with the Prima engine and FIAT jumped in with the announcement of theirs. I think it is still fair to say that Perkins were the first with a DI car engine, the delay was with the car in which it was fitted.
Steve, I feel sure your brother is correct in saying that the 2-stage injectors weren't used in the vans (see my previous posting). I think they were only used in the car, and perhaps only in the turbocharged Montego version. My memory is a bit weak on this (almost 20 years ago now!).
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dtd,
I agree with Steve that the type of injection system on the Octavia will affect the noise it makes. If it is a PD system then I would expect Skoda/VW to have taken advantage of this and used the electronics to feed in the fuel at a controlled rate so as to prevent noisy, explosion-like, combustion.
I believe the Fabia Sdi system is *not* PD but the Octavia's may well be, given that it is a heavier and more up-market car. I have tried to find design information on Skoda's diesels but this is proving difficult (I haven't yet asked Skoda themselves). Any information will be gratefully received.
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At present there aren't any PD engines in the Octavia range. PDs only available in Fabia and Superb. Octavias run the VW TDI engine that has been knocking (no pun intended) about for some time. They're still perfectly good though. Whatever infomration you do manage to turn up would be interesting.
Matthew Kelly
No, not that one.
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