Fuel injectors

[rallen]

Are these electrically operated? Do they inject fuel directly into the cylinders by-passing the valves?

If they are electrical, what would happen if say, 2 out of 6 suddenly stopped working (ie had electrical power removed) ?

I understand about engine smoothness and firing order, on the above example/question assume the two injectors that were being "disconnected" were carefully chosen so that the firing order is preserved.

 

[jberks]

I would imagine the engine management warning light would come on. - I don't think this is your question though!

As there would be no fuel to the cylinder, it would presumably behave in exacly the same way as if you removed the plug lead - e.g. a misfire.

I know i made this point in the other posting - but I can't see how this could be achieved whilst keeping the firing order preserved. In order to keep even running, you need to spread the gaps between firing evenly across the crank rotation cycle. This can be done if you have a V8 as you simply have 1, miss 2, 3, miss 4 etc, A V12 would equally be capable of dropping to a V6, but with a 6 pot, you would have 1, miss2, 3, miss4, 5, 6. You would really have to miss 6 too in order to maintain even-ness, but that would put you on a 3 bang cycle with is uneven by nature. Factor in a V formation and you have a badly rocking engine. Perhaps a W6 would work? Though I still recon that anything less than a 4 bang cycle is uneven and lawnmower-like by nature.

There is always the 5 cylinder engine (270CDI for example) that weakens my theory somewhat, but I would imagine there is some form of weighted balancer at play here to make it think its a 6 cyl.

Interesting thought though. Anyone have any other ideas?

 

[rallen]

I think the firing order concerns itself with the location of the pistons relative to the block, not the position of the crankshaft. In other words a 4 stroke, 4 cylinder engine needs to distribute the 4 strokes evently around one rotation, but which cylinders?! It is never 1-2-3-4, usually it is 1-3-2-4 or something.

 

[jberks]

Absolutely, I believe the order is determined by the position on the block. The shape on the crank is then designed to tie up. Theoretically you can have the crank shaped for any firing order, but the block is the block. A cycle is still effectively 2 rotations of the crank though.
It it went 1234, a pulse would flow through the block from side to side or front to back and the block would bob back and forth, hence the 1342 cycle, so that the pulse from 3 (at the back) counters 1 (at the front) etc and keeps it smooth. The more pulses per cycle, the better the linear effect, provided the vibration from each pulse is countered by an opposing one cylinder firing immediately after. If the frequency is high enough it gives the appearance of a linear flow and hence why any engine appears to shake if the revs drop too low. A 1234 cycle would drone if the revs were high enough.

For this reason, if you removed 1 pulse (cylinder), you need to also remove the opposing one. But, if the 6 pulses are spread evenly thoughout the cycle, and you remove one set of 2 out of the 6, you will have a shorter gap between some pulses than others e.g 1,2,.,4,.,6,1,2,.,4,.,6 etc This would feel like uneven running or surging. With a V8 you can have 1,.,3,.,5,.,7,.,1,.,3 etc and keep it even.

I should add that I am a computer consultant not a mechanic, so I could be wrong, but this is my view.
cheers,
JB

 

[rallen]

I agree with my limited knowledge and so if we remove carefully 2 out of 6 we should not affect the pusle effect too much?

But apart from the pulse effect, is there anything else that might be happening if 2 injectors suddenly stop?

 

[jberks]

I do think that it would impact the flow too much on a V6. (see the description I've just added to my note above) Aside from that, there could be detrimental heating effects as some cylinders would be colder than others. so I suspect there could be problems around this, possibly related to lubrication and clearances though I'm not exactly sure of the exact physics.

 

[rallen]

I am itching to try ti, tomorrow I will try to find the wires to the injectors and see if I can unplug a few while my wife drives the car during the week

 

[jberks]

SO, I'm not the onlyone who finds the MPG dropping through the floor when the wife gets the keys! A doorstop screwed to the underside of the throttle pedal may be worth considering!

 

[paulcallender]

The firing order is evenly spaced, so whatever cylinder you disabled, you'd get (6 cylinder):

fire-fire-miss-fire-fire-fire

If you disabled 2 cylinders, you'd get:

fire-fire-miss-fire-fire-miss

And if you disabled 3, you could potentially be 'in balance' again:

fire-miss-fire-miss-fire-miss

but your engine would run very lumpy. I believe there is another thread which discusses this and the practical (lower) limit is a V8 which can run like a 4 cylinder engine.


In any case, you'd also have to disable the compression of air. It would not be enough to 'jam' open the exhaust valve, becuase when you start and the cold start valve actuates, fuel/air mix would flow right into the exhaust and cause severe problems.

So, you'd have to completely re-engineer the engine, to facilitate this. And all you'd gain is a slightly more efficient low power scenario. Why not just choose the 4 cylinder model?

Here is a top tip for using less fuel - press the throttle pedal more gently. This will simultaneously allow less air and less fuel into the engine.

 

[rallen]

My knowlegde of piston engines obviously is not up to scratch. Why would I have to mess with the valves? Let the piston compress the air, and let the sparkplug ignite afterwards and let there be just air pushed out through the output valve. Why would that be a problem? (other than compressing the air may steal some power)

 

[paulcallender]

(other than compressing the air may steal some power)

Got it in one!

 

[Copiertech]

it will steal a lot of power. try putting a socket bar on the crank and turn the engine. now take the spark plugs out and do the same.

 

[davidsl500]

take the plugs out then and screw in a couple of those duck decoy whistles in place instead and then you can play a tune........

 

[996jimbo]

take the plugs out then and screw in a couple of those duck decoy whistles in place instead and then you can play a tune........

Just sprayed coffee over my screen.

 

[rallen]

Would
[Full engine ] - [ 3 cylinders ] + [loss due to useless air compression ]
more economical than
[Full engine ]

??

 

[jberks]

You would effectively be running a highly inneficient 3 cylinder as against a fairly efficient 6. The power extracted from the fuel would be 1/2 of the normal produced, but would have to overcome the extra overhead of driving all the extra engine, plus compression and any energy needed to overcome the out of balance situation. So, you would see proportionately less energy at the wheels for the same fuel supplied. e.g. 1/2 normal fuel used but 1/6 normal energy getting to the wheels.
So, on the one side, yes you'll use less fuel, but on the other, the car probably wouldn't move.
You could double the throttle input to overcome this, but this puts the fuel usage back to normal, and the engine still has the inneficiency of the extra compression to overcome, so normal fuel but 1/2 power. Add in the inneficiency of an engine running flat out and not having time to burn all the fuel and power extracted per litre of fuel drops off further.
So, no, I don't think so.

 

[davidsl500]

Plus you would have a hell of a job trying to start it! You would have to start it on 6 and then "kill" 3 cylinders - this would inevitably shorten the cat life as some unburnt fuel would exhausted as you killed the cylinders.

Tickover would have to be increased enormously just to keep the thing running. If you know someone with an older car ie., precat then just drop a plug lead off or two and see the effect...

You could reduce the load buy taking the spark plugs out of the disused cylinders - but then you have the original problem of starting it again and spraying the engine compartment with traces of oil - and sucking in dust and grit as the piston cycles - plus the noise.

Interesting idea though.

 

[spannerman]

Don't Mercedes already employ some such technology on the S500/600 whereby on motorway cruising, some cylinders shut down until called-on again for more power/acceleration?

 

[evade]

A few years ago I read a book about jags & the the guy who designed the XJ12 engine continued to experiment with the engine & found that if he set it up to run on 6 cylinders up to 100mph & then switched in the other 6 cylinders above 100mph he found little loss of performance with a increase of economy.
don't no why they never did it in production - use to get about 12mpg from mine. :lol: