The term DC has come into being as a matter of convention. It's a convent way that's been accepted as the norm, to discribe a design consideration when discussing injectors.
It's just something that's evolved.
In talking about injectors, each group, has a specific min on time, and specific off time for it to function properly. The min on and off times are effected by operating voltage. The injector turn on time decreases with the increase in voltage.
If you can find any of the DIY-EFI Flow Bench pics still on line, there are some pics showing how the flow begins as an injector opens. Intially it's just a few globs. No at all like the spray pics people show of a fully open injector. Depending on injector, and a host of variables, at idle, as much as 50% of the PW time at idle is just about the injector discharging globbules. And some injectors generate globules as they close.
When you turn a coil of wire off, the voltage doesn't instant disappear. In the case of an ignition coil the point open signal causes the voltage in the coil to ring, rather then shut off, this ringing back thru the secondary coil is what boosts the voltage up high enough to bridge the gaps in the secondary side. Anyway, this ringing of voltage takes place in the injector as it's turned off. So it can't close until the voltage in the coil decays and the magnetic field collapses. This takes time. The amount of voltage to keep the injector open is going to vary by the injectors design. Two primary elements are weight, and the way the injector deals with stopping the actual flow of fuel.
There is no way, that I've seen to close an injector instantly, some get close, but again not instantly. So as long as it can't close instantly there will be a gray area. Call it what you want, but the injector will behave erratically as the variables to a slight degree will vary. While slight in some applications, just the pressure surges with in the fuel rail can cause poor injector behaviour. You might even see the injector going richer then prescribed, then the flow dropping, ie going lean, and then the flow increasing again.
Least this is how it looks to me, from what I've read and looked at, and again looking at some DC files will show how at times, at high DCs, the O2s drop, and knock begins.
It's just something that's evolved.
In talking about injectors, each group, has a specific min on time, and specific off time for it to function properly. The min on and off times are effected by operating voltage. The injector turn on time decreases with the increase in voltage.
If you can find any of the DIY-EFI Flow Bench pics still on line, there are some pics showing how the flow begins as an injector opens. Intially it's just a few globs. No at all like the spray pics people show of a fully open injector. Depending on injector, and a host of variables, at idle, as much as 50% of the PW time at idle is just about the injector discharging globbules. And some injectors generate globules as they close.
When you turn a coil of wire off, the voltage doesn't instant disappear. In the case of an ignition coil the point open signal causes the voltage in the coil to ring, rather then shut off, this ringing back thru the secondary coil is what boosts the voltage up high enough to bridge the gaps in the secondary side. Anyway, this ringing of voltage takes place in the injector as it's turned off. So it can't close until the voltage in the coil decays and the magnetic field collapses. This takes time. The amount of voltage to keep the injector open is going to vary by the injectors design. Two primary elements are weight, and the way the injector deals with stopping the actual flow of fuel.
There is no way, that I've seen to close an injector instantly, some get close, but again not instantly. So as long as it can't close instantly there will be a gray area. Call it what you want, but the injector will behave erratically as the variables to a slight degree will vary. While slight in some applications, just the pressure surges with in the fuel rail can cause poor injector behaviour. You might even see the injector going richer then prescribed, then the flow dropping, ie going lean, and then the flow increasing again.
Least this is how it looks to me, from what I've read and looked at, and again looking at some DC files will show how at times, at high DCs, the O2s drop, and knock begins.
