Bruce
02-06-2004, 07:48 AM
There are 3 different injector firing strategies.
Bank To Bank
SEFI
and
Batch fire.
Batch fire is firing the injectors once pre engine revoltion.
SEFI is firing each cylinder, once every two engine revolutions. On the GNs the injector fires at a closed intake valve, but, there are some other SEFIs that fire at an open intake valve.
Bank to bank is just firing half the injectors every engine revolution.
Both B2B, and SEFI allow for longer Pulse Widths, since the injectors fire half as often as the Batch fire system. So at idle this allows for being able to run large injectors more preciously, at the lower speeds. At too short of pulse widths, injectors can get slightly erratic, and have a lousy idle.
While at a glance both B2B, adn SEFI look better, then batch, there are cases where batch is better. If your running *not too* large of injector, then with the injectors firing twice as often, they do a better job of atomization.
With the way the injectors point in the manifold, at all the lower engine speeds the fuel is just being blown onto the runner floor. So that does alot toward negating some allegeded benefits.
Also, what gets the fuel into small enough droplets to burn is mostly accompliced by what happens at over lap. As the exhaust valve is closing, and the intake first cracks open there is a blast of exhaust past the intake valve, and this blast of hot air, ATOMIZES the fuel waiting behind the intake valve. While this doesn't sound right, Ford has spent a bunch of research money documenting this. Atta glance one would think that if anything was going to happen it would be from the high EGT vaporizing the fuel under those conditions, but again what seems logical just isn't always in practice what you may think.
And another little tid bit is from Sir Harry Ricardo where he explains how a fuel droplet actually burns. He compares a fuel droplet to an onion. And that during the combustion reaction that the fuel burns off as would the layers of an onion would. And it might be mentioned rain drops have the least surface area for volume as possible. Which isn't as good as having the greatest surface volume, would be for the combustion process. So while atomization is nice, vaporization and it's smaller droplets (gas) can make for a faster combustion process.
Bank To Bank
SEFI
and
Batch fire.
Batch fire is firing the injectors once pre engine revoltion.
SEFI is firing each cylinder, once every two engine revolutions. On the GNs the injector fires at a closed intake valve, but, there are some other SEFIs that fire at an open intake valve.
Bank to bank is just firing half the injectors every engine revolution.
Both B2B, and SEFI allow for longer Pulse Widths, since the injectors fire half as often as the Batch fire system. So at idle this allows for being able to run large injectors more preciously, at the lower speeds. At too short of pulse widths, injectors can get slightly erratic, and have a lousy idle.
While at a glance both B2B, adn SEFI look better, then batch, there are cases where batch is better. If your running *not too* large of injector, then with the injectors firing twice as often, they do a better job of atomization.
With the way the injectors point in the manifold, at all the lower engine speeds the fuel is just being blown onto the runner floor. So that does alot toward negating some allegeded benefits.
Also, what gets the fuel into small enough droplets to burn is mostly accompliced by what happens at over lap. As the exhaust valve is closing, and the intake first cracks open there is a blast of exhaust past the intake valve, and this blast of hot air, ATOMIZES the fuel waiting behind the intake valve. While this doesn't sound right, Ford has spent a bunch of research money documenting this. Atta glance one would think that if anything was going to happen it would be from the high EGT vaporizing the fuel under those conditions, but again what seems logical just isn't always in practice what you may think.
And another little tid bit is from Sir Harry Ricardo where he explains how a fuel droplet actually burns. He compares a fuel droplet to an onion. And that during the combustion reaction that the fuel burns off as would the layers of an onion would. And it might be mentioned rain drops have the least surface area for volume as possible. Which isn't as good as having the greatest surface volume, would be for the combustion process. So while atomization is nice, vaporization and it's smaller droplets (gas) can make for a faster combustion process.