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Charles Murray
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On the downstroke
Charles Murray   10/10/2011 12:27:06 PM
Interesting that Ford mentioned the piston is already on the downstroke when it fires. We heard the same from the engineers at Scuderi, who are using that stretegy on their split-cycle engine. Firing after top dead center is said to put more energy on the piston's downward stroke which results in more power on the crankshaft.

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So why does AFTC work here when std engines fire BTDC?
rcwithlime   10/11/2011 11:58:32 AM
Igniting the mixture before the piston reaches TDC will allow the mixture to fully burn soon after the piston reaches TDC. If the air-fuel mixture is ignited at the correct time, maximum pressure in the cylinder will occur sometime after the piston reaches TDC allowing the ignited mixture to push the piston down the cylinder with the greatest force. Ideally, the time at which the mixture should be fully burnt is about 20 degrees ATDC. This will utilize the engine's power producing potential. If the ignition spark occurs at a position that is too advanced relative to piston position, the rapidly expanding air-fuel mixture can actually push against the piston still moving up, causing knocking (pinging) and possible engine damage. If the spark occurs too retarded relative to the piston position, maximum cylinder pressure will occur after the piston is already traveling too far down the cylinder. This results in lost power, high emissions, and unburned fuel.

I understand they have varied valve timing, etc. but wish Iknew why firing ATDC (After top dead center) now works better for more HP,less emmisions, and better fuel economy when other (and previous) designs fire BTDC (Before top dead center) Why are not similar mods not used in standard or current motors?

Sawmill Engineer
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Looks interesting, but...
Sawmill Engineer   10/11/2011 12:19:30 PM
This is vaguely reminiscent of the old Pontiac turbo Firefly.  It had a 3 cylinder, 1,000 CC Suzuki engine with a tiny little turbo on it.  I think the turbo took the engine to a princely 80-odd hp.  It was a heck of a lot of fun to drive--blowing the doors off of the monster pickup crowd on double-lane uphills and other testosterone laden silliness!

The turbo in the Ford engine doesn't add to the efficiency, just stuffs more air in each cylinder so more fuel can be burnt when the power is required.  I raised my eyebrows when seeing the comment about cooling the exhaust gases by a built-in header in the cylinder head--it seems to be counterintuitive when hanging a turbo in the exhaust.  Don't you need the hottest gases you can get to operate the turbo? 

The interesting part is the offset crank-I'm real curious just how much this adds to the engine efficiency.  This isn't a new idea, but using crank offset to change the point where ignition occurs in the crankshaft-conrod-piston geometry is very clever.  There should also be some further efficiency gain since the piston will have a slightly better mechanical advantage on the crankshaft during the power stroke.

I will certainly be watching for further information on this engine!





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Re: On the downstroke
mhs64   10/11/2011 3:26:04 PM
I noticed that he mentioned that it was in the down stroke at firing while talking about the offset crank.  With the crank offset, when the piston is at TDC, the connecting rod will be heading down (or up, if offset the other direction).  I'm guessing he is referring to that.

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Nice But...
microengineer   10/11/2011 4:19:48 PM
I can appreciate increased fuel mileage as worth goal, but not sure the average American (with the exception of those content to drive econo-boxes) will accept that level of horsepower.  I would assume the vehicel it powers will be light & have high road noise due to the need for reduced weight.

From what I've read, Ford would do well to spend time in designing a transmission that would actually last.

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Here's why does AFTC work
Cat-Man   10/11/2011 5:11:08 PM
Anytime the combustion occurs prior to TDC it takes additional power to compress the growing flame front as the piston is fighting not only to compress the A:F mixture - it is an accepted fact of life in the Otto Cycle Engine. The old trick of firing 10-20-30 degrees before TDC it taxes power in an effort to make power. FORD has obviously designed the combustion chamber, mixture and mixture distribution for a very fast burn - so fast in fact there is no need to be paying the early ignition "tax" and taking that wasted of power . Bravo FoMoCo!

TJ McDermott
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Re: Nice But...
TJ McDermott   10/12/2011 7:06:45 AM
98hp.  OK, I can accept that, if everyone else will.  This engine is for a commuter car, and that's how most people drive.  But if only a few percent drive the lightweight vehicle for which this engine is intended, then the drivers will have a higher rate of injury.

One could as easily mandate all commuters drive motor scooters for their daily drive.  If everyone were atop one of those, fuel problems would go away, no new roads would be needed because of more room on the existing roads.

Until EVERYONE is in smaller vehicles, I'd be nervous in a fly-weight vehicle while behemoth heavy-weight ones surround me on the road.

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ignition timing
jonwexler   10/12/2011 12:51:22 PM
Ford has extra degrees of freedom here, because of direct injection.  They can run a high compression ratio even with the turbocharger.  The spark can come just after the beginning of the injection and there is no possibility of detonation, because there isn't enough charge present and it hasn't developed the free radicals that promote detonation.  Also the timing and duration of the injection will control combustion variables.


I agree that having a cooled exhaust manifold is counterproductive for the turbo.  Maybe they are able to have an effective turbo anyway and use less exotic materials on the hot side?



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