Blownoiler
New member
- Joined
- Oct 26, 2012
- Messages
- 23
IDI injection pop-off pressure
I'm trying to work out the best pop-off pressure for the pintle injectors in my 3.1 litre Isuzu IDI TD. There doesn't seem to be a lot of info around on what happens inside the chamber when pop-off pressures are increased/decreased in an IDI, so I thought that I'd bring the subject up here to see if anyone has any insight on this type of mod.
There is a complication that I should bring up now, and that is the fuel being utilized is used cooking oil which doesn't atomise as well as what diesel fuel does, and doesn't burn as completely either.
The Isuzu factory workshop manual gives the standard pop pressure of 2133 psi for this engine (4gj2T), yet other Isuzu engines that have the same injection pump have higher pop pressures, indicating that the pump is capable of handling a reasonable pressure increase without throwing in the towel. The 4JB1T engine which runs the same pump has a 2631 psi injector pop pressure, and interestingly the malaysion/argentinian model of the same engine has a 3128 pop pressure listed, probably for emmision purposes I'm thinking.
Given that the factory offered a warranty on these engines that ulilize these higher pressures I'm confident that no major pump problems will arise from a substantial increase in my engines operating injector pop pressure.
I'm still tring to understand what changes occur involving the ignition/burn characteristics when the pop pressure is changed from the standard setting , and am thinking that the shot of fuel could benefit from being injected at higher pressure for the better atomisation, which theoretically should increase the burn rate and result in less unburnt fuel, which we see as soot/smoke.
Increasing the pop pressure of the injectors should theoretically retard the start of injection, yet the increased atomisation of the fuel along with the faster rate of the injection (due to the higher injection pressure) should lead to the combustion chamber peak pressure being reached earlier , which would have the effect of advancing the injection timing. So, what is going to happen regarding the time it takes to reach the chamber peak pressure with much higher injection pressures?
Also, I would expect better fuel efficiency with a higher injection pressure setting, yet have heard people claim that they got better mileage from lowering injector pop pressure, .....so, If I increase my idi's injector pop pressure from the current 2133 psi to 3128 psi what can I expect in terms of efficiency?
I'm trying to work out the best pop-off pressure for the pintle injectors in my 3.1 litre Isuzu IDI TD. There doesn't seem to be a lot of info around on what happens inside the chamber when pop-off pressures are increased/decreased in an IDI, so I thought that I'd bring the subject up here to see if anyone has any insight on this type of mod.
There is a complication that I should bring up now, and that is the fuel being utilized is used cooking oil which doesn't atomise as well as what diesel fuel does, and doesn't burn as completely either.
The Isuzu factory workshop manual gives the standard pop pressure of 2133 psi for this engine (4gj2T), yet other Isuzu engines that have the same injection pump have higher pop pressures, indicating that the pump is capable of handling a reasonable pressure increase without throwing in the towel. The 4JB1T engine which runs the same pump has a 2631 psi injector pop pressure, and interestingly the malaysion/argentinian model of the same engine has a 3128 pop pressure listed, probably for emmision purposes I'm thinking.
Given that the factory offered a warranty on these engines that ulilize these higher pressures I'm confident that no major pump problems will arise from a substantial increase in my engines operating injector pop pressure.
I'm still tring to understand what changes occur involving the ignition/burn characteristics when the pop pressure is changed from the standard setting , and am thinking that the shot of fuel could benefit from being injected at higher pressure for the better atomisation, which theoretically should increase the burn rate and result in less unburnt fuel, which we see as soot/smoke.
Increasing the pop pressure of the injectors should theoretically retard the start of injection, yet the increased atomisation of the fuel along with the faster rate of the injection (due to the higher injection pressure) should lead to the combustion chamber peak pressure being reached earlier , which would have the effect of advancing the injection timing. So, what is going to happen regarding the time it takes to reach the chamber peak pressure with much higher injection pressures?
Also, I would expect better fuel efficiency with a higher injection pressure setting, yet have heard people claim that they got better mileage from lowering injector pop pressure, .....so, If I increase my idi's injector pop pressure from the current 2133 psi to 3128 psi what can I expect in terms of efficiency?