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Old 12-19-2016, 08:32 PM   #21 (permalink)
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Quote:
Originally Posted by oldtamiyaphile View Post
Stop/ Start is actually more common on diesels. Eg Renault Kangoo and Fiat Doblo have S/S on their diesels, but it's not an option on petrol versions. I think all Euro diesels across the board have it, no doubt because they're all very close to various emissions limits.

I have S/S on my Trafic and while it's early days, I don't seem to be getting a lot of DPF regen cycles. Sitting and idling doesn't do a DPF any good either, the EGT's are low and so it's just filling with soot, it may well be better to stop the engine. Of course, S/S is inhibited during a DPF regen.
Being from Brazil I haven't got so much contact with the newest small Diesels. But the facelifted Ranger actually got rid of the DPF and is still rated Euro-5.

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Old 12-21-2016, 02:17 PM   #22 (permalink)
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That's mostly referring to downsized turbo engines on larger cars.

Even with direct injection helping in cooling, heat is a problem that cannot be sidestepped with engines producing two to three times the power of their naturally aspirated kin.

Naturally aspirated 1.0s will still continue to be viable for subcompact applications. But as emissions loopholes close, expect the huge power densities we're getting out of modern cars (indeed, we're experiencing a new renaissance of power here) to slowly go away.
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Old 12-22-2016, 02:30 PM   #23 (permalink)
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Quite informative.

My 2009 auto Corolla with 321,000km (over 200,000 miles) hangs in the middle of that pack easily even though it weighs the same as the Focus that is in last place. I won't be trading it in anytime soon.
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Old 12-23-2016, 09:21 AM   #24 (permalink)
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re: "poor" FE performance of small engines

Quote:
Originally Posted by niky View Post
That's mostly referring to downsized turbo engines on larger cars.

Naturally aspirated 1.0s will still continue to be viable for subcompact applications.
Thanks for pointing this out.

That article about the "failure" of smaller (usually turbo) engines to deliver real world fuel savings got a lot of attention recently and I found nobody making that distinction.
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Old 12-23-2016, 01:14 PM   #25 (permalink)
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It's probably a good thing that emissions testing continues to evolve to mirror real-world driving. I wonder if we'll see a move toward more rolling cylinder deactivation, rather than bigger displacements for the sake of it. Perhaps we'll even see it on hybrids, once the emissions standards really tighten up.

Heck, I could probably be happy as a clam driving my Outback around on one or two cylinders most of the time, if it weren't for the NVH that would cause.
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Old 12-23-2016, 01:35 PM   #26 (permalink)
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Quote:
Originally Posted by ThermionicScott View Post
It's probably a good thing that emissions testing continues to evolve to mirror real-world driving. I wonder if we'll see a move toward more rolling cylinder deactivation, rather than bigger displacements for the sake of it. Perhaps we'll even see it on hybrids, once the emissions standards really tighten up.

Heck, I could probably be happy as a clam driving my Outback around on one or two cylinders most of the time, if it weren't for the NVH that would cause.
As I understand it, there are two good reasons we see 3 cylinder 1.0's and 1.2's rather than 4 cylinder, and I can speculate on a few more.

1) 3 cylinder and 5 cylinder engines have some inherent efficiency advantages due to the timing of the exhaust pulses over the more balanced 4 and 6 cylinder engines.

2) Volume of a cylinder goes up cublicly while surface area goes up by the square as you increase cylinder size. For this reason, a 1.0L 3 cylinder has less frictional surface and less surface through which to lose heat and therefore thermodynamic efficiency. A 1.0L 2 cylinder or even 1 cylinder would be even better in this respect, but it would probably rattle your teeth out.

Speculation on my part, but due to the flame speed of gasoline combustion, there will be a (maybe more than one?) Goldilocks zone for cylinder bore and stroke at a given RPM. If a cylinder's stroke gets shorter, you need to compensate by increasing the RPM to keep piston speed in that zone or you'll lose efficiency, and (if I remember correctly) friction goes up by the square of RPM, which you'd really want to avoid.

This is not something I've read anywhere, just something I've put together myself after thinking about it a good deal. Someone please correct me if I'm wrong.
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Old 12-23-2016, 01:54 PM   #27 (permalink)
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Good food for thought, Ecky! It all makes sense to me. Do you suppose the messed-up exhaust pulses and still-present moving friction are why we don't see a lot more efficiency gains from cylinder deactivation? Most estimates I've read are in the single digit %.

(For others: I had speculated that 4-cylinder engines with rolling cylinder deactivation might replace 3-cylinders, but decided it was extraneous and edited it out of my original post just before Ecky replied. I need to stop obsessively editing posts and leave them be. )
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Old 12-23-2016, 01:59 PM   #28 (permalink)
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I'm certain those contribute. A piston acting as an air spring with closed valves still has friction, and it will undoubtedly affect an exhaust not tuned for it. I'm nowhere near an expert on the matter, just someone who reads crap on the internet, but it stands to reason.

I think it would be neat to see a pair of 2 cylinder engines mated together at the crank with a clutch in between, so half of the engine could be truly deactivated.
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Old 12-24-2016, 04:23 AM   #29 (permalink)
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Quote:
Originally Posted by Ecky View Post
As I understand it, there are two good reasons we see 3 cylinder 1.0's and 1.2's rather than 4 cylinder, and I can speculate on a few more.

1) 3 cylinder and 5 cylinder engines have some inherent efficiency advantages due to the timing of the exhaust pulses over the more balanced 4 and 6 cylinder engines.

2) Volume of a cylinder goes up cublicly while surface area goes up by the square as you increase cylinder size. For this reason, a 1.0L 3 cylinder has less frictional surface and less surface through which to lose heat and therefore thermodynamic efficiency. A 1.0L 2 cylinder or even 1 cylinder would be even better in this respect, but it would probably rattle your teeth out.

Speculation on my part, but due to the flame speed of gasoline combustion, there will be a (maybe more than one?) Goldilocks zone for cylinder bore and stroke at a given RPM. If a cylinder's stroke gets shorter, you need to compensate by increasing the RPM to keep piston speed in that zone or you'll lose efficiency, and (if I remember correctly) friction goes up by the square of RPM, which you'd really want to avoid.

This is not something I've read anywhere, just something I've put together myself after thinking about it a good deal. Someone please correct me if I'm wrong.
There's also the question of how much combustion chamber real estate you can set aside for direct injection, which has to share that space with four valves and a spark-plug.

I recall Hyundai-Kia stating there were issues with putting direct injection on something smaller than a four-cylinder 1.6. But that was years ago... and we've come a long way since then... Obviously, it can be done and has been done, as we're seeing a lot of 1.5 liter four-cylinder DI engines... but other manufacturers are going for 1.5 three-pots to give themselves more wiggle room in cylinder head development.
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Old 12-24-2016, 10:05 AM   #30 (permalink)
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Is the Ford 1.0T direct injected?

Google is my friend! Yes: DI.

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