Someone has just told me that all four injectors in a rail fire at the same moment.
Can this be true? I had assumed that the reason for one injector per cylinder was so that each was timed precisely for the correct point on that cylinder\'s cycle.
I thought the whole point about fuel injection was that it replaced the inevitable hit and miss suck and dribble from a carburettor with a precisely timed and measured squirt to each cylinder.
Anybody care to comment on this?
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May be an element of truth in that.bearing in mind as a engine speeds up and I mean to around formula 1 type speeds then timing of injection as is spark must both be almost at same time.at normal speeds though if that were the case what would be the point of an ECU.I doubt that is the case.
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Many thanks - there\'s some useful stuff at \"howstuffworks\"!
So it seems that they could all open at the same time, but better if they did so sequentially.
I don\'t understand though how it could work very well if they did open simultaneously. Wouldn\'t some of the fuel simply be wasted squirting at a closed valve? And if a continuous stream of fuel is OK, well, isn\'t that what a carburettor does?
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>>So it seems that they could all open at the same time, but better if they did so sequentially
That is the way it does work but on high speed engines the theory is that due to time between solenoid cut of and re-opening the time difference is so small making it possible for the injectors to be running all at once.I havent explained properly I know but I hope you get the idea.
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Simply put earlier injection systems like Bosch L Used to squirt all the injectors simultaneously on each induction stroke of each cylinder on a 4 cyl. So effectively you would get one squirt onto the back of the valve and one into the cylinder past the open valve. Because the boffins are clever they could calculate precisely the amount of fuel needed to make it right. Then since about 1992 onwards virtually everything became sequential and extra fuel is made available by multiple pulsing of the injectors etc etc. Clever stuff until we start shoving supermarket petrol into them and coking everything up with extended service intervals and the 200 yard school run!
Andrew
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Simplicate and add lightness!!
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Thanks Andrew - very clearly explained.
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great - very clearly explained - so how does DIRECT INJECTION, like the Golf FSI engines, work ?
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arnold2
Direct injection uses the diesel engine principle. Instead of injecting petrol into the inlet manifold at relatively low pressure, a DI engine injects the fuel into each combustion chamber under high pressure at just the right point in the operating cycle.
Regards
John S
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Andrew
Was the L jetronic that bad? Heavens, I thought it was at least sequential! If I recall correctly I owned an \'87 Orion with the injected engine featurng the earlier K jetronic system. I was amazed to find that was even simpler and used continuous injection into the inlet manifold!
Regards
John S
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With the L Jetronic, at wide open throttle and at an RPM (determined by the value of a resistor within the ECU) - typically 3000 rpm, the injectors would spray continuously! You could change this resister to get continuous spraying at lower rpm, more power, much lower fuel economy.
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All modern injection systems fire the injector at the appropriate time for the cylinder. The older systems which had common injector firing fell out of favour due to efficiency and backwash, i.e. the first pulse of fuel that lay on the back of the hot inlet valve evaporates and warms the pocket of air in the inlet manifold thus reducing the air density and loosing efficiency of combustion at higher rpm. With the advent of unleaded fuel and newer design of combustion chambers and swirl pots a single pulse is used the duration of which is controlled by the ECU, and mixture requirements whilst the timing of the pulse is controlled by piston position, rotational speed and any input from variable valve timing and even in some cases the ratio between the engine speed and the road speed thus the gear you are in. All these inputs are processed by the ECU and mapped to provide maximum efficiency, maximum grunt or maximum rpm. Direct injection has been the latest advance thus breaking the restraints of inlet valve timing and injection timing. This allows the fuel to be injected at any chosen position of the piston. I have read in a trade mag that this even reduces engine wear because the fuel is not drawn in on the down stroke thus washing some lubrication off the cylinder wall. The fuel is injected directly at a much later point and even into the upstroke of the piston. This increase both combustion efficiency and power per cc.
Diesels use this method to great advantage as prior to direct injection the fuel ignited when the pressure during the combustion stroke reaches about 160 psi. Now direct injection adds the controlled measure of fuel at the optimum point of the combustion cycle. The problem here is the pressure to inject the fuel at the right moment is greater than the flash point of the fuel so the diesel injector is a unique beast and operates at in excess of 1000Bar ( the new HP Bosch injector runs at 2000bar). This pressure is generated in the injector as it has an internal solenoid type pump that ejects the fuel before the diesel self combusts. This has bought a new lease of life to diesel engine efficiency and power output and also runs cleaner. I’m worn out now and need a lie down but I hope that helps. Regards Peter
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Gosh yes, Peter, you deserve your rest. I'd wondered about direct injection too, but was saving that for another thread.
So basically, "fuel injection" has come a long way, from little more than the accelerator pump that some carburettors had, to the full blown proper injection used in diesels.
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"Kugelfischer" was direct injection."K" was indirect injction;"KE" was trimmed by the Lambda sensor.
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