h a l f b a k e r yQuis custodiet the custard?
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When an internal combustion engine is running at part load , can we switch-off fuel supply to selected cylinders and a special vent can be provided on each cylinder head which will open so that the particular cylinder will go out of the service temporarily and over all engine will run on full load .
Thus efficiency can be maintained.
the new version
http://popularmecha...3/9911AUNCWFKM.html
part way down, variable displacement [rbl, Aug 13 2002, last modified Oct 04 2004]
Variable cylinder use
http://www.motortre...0618_hon/index.html
Honda does this [bungston, Jun 23 2008]
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Annotation:
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Kind of like the variable valve timing on an Alfa Romeo? (ok, different implementation, similar result) |
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Cadilac tried this in the early 80's with a V4/6/8 and that
car was a disaster. It never ran correctly and ownwers
just ended up unplugging the computer so that it stayed
as a V8. |
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Times have changed and computers are more powerful so
who knows... |
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Modern fuel-injection systems already monitor engine load and meter the fuel accordingly. In this way, all cylinders receive the appropriate amount of fuel, rather than half of them receiving full charge and the other half receiving none. The Bosch L-Jetronic unit switches off the fuel completely when the vehicle is exceeding 38mph with the accelerator closed. |
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My '92 Volvo shuts down all fuel flow above 2500 revs when the accelerator is released. |
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Volvo use Douvrin engines which, I believe, are fitted with Bosch injection systems. The same unit is on my '92 Carlton. |
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I'm told that it's the same engine as a Renault 21 of the same era. |
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see link, very very baked. |
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Buy a Honda Hybrid Gas/Electric car, if you're trying to conserve fuel.. (and they sound like little weed whippers tooling around town) |
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[Mayfly]: And the Peugeot 605, if memory serves. Those three companies all use Douvrin engines, so there's plenty of crossover. |
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UB, surely this would cause excessive engine braking, as the out-of-use cylinders would pressurise on the compression cycle. |
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When working on motorcycle cam shafts/crankshafts/gearboxes/clutches, I have always removed the spark plugs. I can then manually crank the engine using a spanner on the end of the final drive shaft. It's a lot easier that fighting the compression. |
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[Mayfly]: Yes, this does cause engine braking, but shirley that's the whole point. You take your foot off the gas because you want to slow down, yes? (Or at least, not maintain acceleration.) Better this way than have the engine fighting the brakes when you brake. |
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//When an internal combustion engine is running at part load//. |
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This suggests cruising speed. Using the engine for braking would be negative load. At cruising speed, engine braking is not required, in fact it is undesirable. Why produce power in four working cylinders and then use most of it up in fighting the other four redundant cylinders? Just produce less power in the four working cylinders and use all that power to drive the wheels by reducing the load of the four redundant cylinders. |
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I don't deny that shutting down all the fuel intakes when the accelerator is fully released is a good thing. That's obviously why Volvo put this system into my car. |
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(And I'm only Shirley at the weekend!) |
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Crap...I've just posted this same reply on the Varying Cylinder Sizes topic...but I'll repeat it here for anyone who hasn't seen it yet. |
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I've read recently that GM has revitalized their efforts in creating a 'displacement on demand' engine...and it's coming along very well. The switch between the various cylinder configurations is very smooth and almost entirely unfelt; it happens within one-half to one revolution of the camshaft, which at a normal operating speed of 1500 rpm would work out to around 1/1500 to 1/750 of a second. That's a very short transition time. They've even implemented this concept on various Corvette and truck engines for testing, and the results were an engine with an equal amount of performance and much better fuel economy. |
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although you would be burning less fuel from the cylinders that were shut down, but in turn the car computer would notice the decrease in power, even if your foots off the accelerator, and end up pushing more gas into the still functioning cylinders, using more fuel |
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It is better to have all the valves on the non-firing cylinders remain closed than open. The pistons will use the compressed air from the compression stroke for power on the power stroke. If the valves were open, the engine would lose power pushing air out and pulling air into the combustion chamber. |
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I had this idea when I was 10. |
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God only knows how I grew up to be so stupid. |
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It now exists, Chrysler has it in their magnum for example, and a few other car manufactureres like BMW and uh... have it also. |
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I had an idea that people suffering from fuel prices could salvage some of the investment in enormous SUVs by having a different and more economical engine inserted. My wife pointed out this would be expensive. She proposed a software fix: have the computer governing the engine use a fewer number of cylinders. This would chiefly help in vehicles that are greatly overpowered for their current use: commuting in an F10 pickup or some such. Lo - a similar idea from the Halfbakery archive. Credit where credit is due. |
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It would be cheaper and easier to install a new software package and use extant machinery. Gearheads: be detailed when tearing this apart, because I hope to learn something about cars. |
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