School me on mechanical fuel injection....
#1
07-31-2014, 12:54 PM
School me on mechanical fuel injection....
Just doing some reading, I already knew the basics, but have a few questions to go over.
OK, so on a mechanical fuel pump, you have the plungers, internal metering, delivery valves, injector fuel lines, pop valves in the injectors, and then the actual injector tip.
So question 1.... the delivery valves; are they a type of check valve? Or are they more a an orifice metering valve?
And does an inline pump have a relief on the high pressure side? If you put a larger pump that is too big for the injectors, does it bleed off what it can't pump, or can it damage the pistons in the pump from over pressuring?
And about the injector hole size and arrangement; I keep reading about injector tip changes effect fuel economy; whats the goal; to get the fuel out as fast as possible, or fine atomization? EG if you go from a 4 hole injector, to a 7 hole, but identical angle and hole size, should it not perform for good MPG? Maybe pop pressure needs to be upped to blow the fuel out faster?
How would 2 identical engines compare; but 1 has 4 hole injectors, and sprays over 30* of rotation, but the other has more holes, and sprays over 18* of rotation?
I guess I'm just asking, what are some good combinations that can be used to push more fuel, but do it for a nice clean burn...
If you have a perfectly running mechanical engine, but want to push more fuel, is it going to be better to aim for a longer injection cycle with more fine atomization, or a quickker injection cycle with more holes?
OK, so on a mechanical fuel pump, you have the plungers, internal metering, delivery valves, injector fuel lines, pop valves in the injectors, and then the actual injector tip.
So question 1.... the delivery valves; are they a type of check valve? Or are they more a an orifice metering valve?
And does an inline pump have a relief on the high pressure side? If you put a larger pump that is too big for the injectors, does it bleed off what it can't pump, or can it damage the pistons in the pump from over pressuring?
And about the injector hole size and arrangement; I keep reading about injector tip changes effect fuel economy; whats the goal; to get the fuel out as fast as possible, or fine atomization? EG if you go from a 4 hole injector, to a 7 hole, but identical angle and hole size, should it not perform for good MPG? Maybe pop pressure needs to be upped to blow the fuel out faster?
How would 2 identical engines compare; but 1 has 4 hole injectors, and sprays over 30* of rotation, but the other has more holes, and sprays over 18* of rotation?
I guess I'm just asking, what are some good combinations that can be used to push more fuel, but do it for a nice clean burn...
If you have a perfectly running mechanical engine, but want to push more fuel, is it going to be better to aim for a longer injection cycle with more fine atomization, or a quickker injection cycle with more holes?
#2
07-31-2014, 04:02 PM
Postmaster
Just doing some reading, I already knew the basics, but have a few questions to go over.
OK, so on a mechanical fuel pump, you have the plungers, internal metering, delivery valves, injector fuel lines, pop valves in the injectors, and then the actual injector tip.
So question 1.... the delivery valves; are they a type of check valve? Or are they more a an orifice metering valve?
They are a check valve that maintains a certain pressure in the injection lines. There is a balance between The swept volume of the valve itself after it seals up and the injector characteristics that controls the pressure in the line. The more pressure in the line (Higher flow DV's with less swept volume after sealing) the more of a chance of post injection events from the line contracting, I.E. dribbling etc. The dribbling is controlled by lowering the pressure in the line, and that is done by increasing the swept volume after the DV closes and retracts. Problem is that the collar that controls that post-seal volume change also restricts flow, and there is more time to build up pressure in the line...
And does an inline pump have a relief on the high pressure side? If you put a larger pump that is too big for the injectors, does it bleed off what it can't pump, or can it damage the pistons in the pump from over pressuring?
No. The reason smaller injectors limit fuel is because these pumps have a pressure limit before they start bleeding past the plungers... That is volume not used. The way to free that up is to run less injection pressure, but then you get a less crisp, longer event... Our DB pumps on the IDI max out at about 12kpsi (provided you have enough volume to get there), A P-pump will do 18kpsi or so, and a Commonrail runs around 20-25kpsi, but the pump doesn't control volume at the cylinder, the injector does, that's why they are so efficient. In a pump like the DB, pressures can spike hard enough to lock the rotor and shear the input, lets if the injector sticks and doesn't open... Big pumps like the P7100 wont be effected.
And about the injector hole size and arrangement; I keep reading about injector tip changes effect fuel economy; whats the goal; to get the fuel out as fast as possible, or fine atomization? EG if you go from a 4 hole injector, to a 7 hole, but identical angle and hole size, should it not perform for good MPG? Maybe pop pressure needs to be upped to blow the fuel out faster?
It depends on many factors in a DI engine, swirl is huge in a DI, and I would argue that's why the heads flow like crap. Swirl is more important than airflow. The general consensus is that less hole qty, is better because the denser mass of the fuel charge penetrates the swirling compressed air charge better than more holes, and less mass, this is fully dependent on how much fuel, air, heat, and a bunch of different factors though, so its hard to make a blanket statement. Obviously the bigger the hole, the better flow, but too much can mean a smoky burn...
How would 2 identical engines compare; but 1 has 4 hole injectors, and sprays over 30* of rotation, but the other has more holes, and sprays over 18* of rotation?
Depends on the setup, RPM range, fuel volume, etc... Fuel only burns at a certain rate, its the constant.
I guess I'm just asking, what are some good combinations that can be used to push more fuel, but do it for a nice clean burn...
More pop pressure results in a higher injection pressure, which means less duration, so that matched with fuel volume is going to be the single best way to tune a particular set of parts/setups... Just have to make sure you don't bump pop pressure so high for a given volume of fuel that it over pressures the pump and cuts volume...
If you have a perfectly running mechanical engine, but want to push more fuel, is it going to be better to aim for a longer injection cycle with more fine atomization, or a quickker injection cycle with more holes?
Longer durations with more volume always result in a slower burn. This can be good if you are trying to spool a big turbo, but generally leads to the fuel being burnt too late and not effectively being turned into torque. Generally you want a shorter duration, which is why you want a higher injection pressure, because the energy is released faster and more torque can be applied over the crank angle "sweet spot" by adjusting where the burn window is at...
OK, so on a mechanical fuel pump, you have the plungers, internal metering, delivery valves, injector fuel lines, pop valves in the injectors, and then the actual injector tip.
So question 1.... the delivery valves; are they a type of check valve? Or are they more a an orifice metering valve?
They are a check valve that maintains a certain pressure in the injection lines. There is a balance between The swept volume of the valve itself after it seals up and the injector characteristics that controls the pressure in the line. The more pressure in the line (Higher flow DV's with less swept volume after sealing) the more of a chance of post injection events from the line contracting, I.E. dribbling etc. The dribbling is controlled by lowering the pressure in the line, and that is done by increasing the swept volume after the DV closes and retracts. Problem is that the collar that controls that post-seal volume change also restricts flow, and there is more time to build up pressure in the line...
And does an inline pump have a relief on the high pressure side? If you put a larger pump that is too big for the injectors, does it bleed off what it can't pump, or can it damage the pistons in the pump from over pressuring?
No. The reason smaller injectors limit fuel is because these pumps have a pressure limit before they start bleeding past the plungers... That is volume not used. The way to free that up is to run less injection pressure, but then you get a less crisp, longer event... Our DB pumps on the IDI max out at about 12kpsi (provided you have enough volume to get there), A P-pump will do 18kpsi or so, and a Commonrail runs around 20-25kpsi, but the pump doesn't control volume at the cylinder, the injector does, that's why they are so efficient. In a pump like the DB, pressures can spike hard enough to lock the rotor and shear the input, lets if the injector sticks and doesn't open... Big pumps like the P7100 wont be effected.
And about the injector hole size and arrangement; I keep reading about injector tip changes effect fuel economy; whats the goal; to get the fuel out as fast as possible, or fine atomization? EG if you go from a 4 hole injector, to a 7 hole, but identical angle and hole size, should it not perform for good MPG? Maybe pop pressure needs to be upped to blow the fuel out faster?
It depends on many factors in a DI engine, swirl is huge in a DI, and I would argue that's why the heads flow like crap. Swirl is more important than airflow. The general consensus is that less hole qty, is better because the denser mass of the fuel charge penetrates the swirling compressed air charge better than more holes, and less mass, this is fully dependent on how much fuel, air, heat, and a bunch of different factors though, so its hard to make a blanket statement. Obviously the bigger the hole, the better flow, but too much can mean a smoky burn...
How would 2 identical engines compare; but 1 has 4 hole injectors, and sprays over 30* of rotation, but the other has more holes, and sprays over 18* of rotation?
Depends on the setup, RPM range, fuel volume, etc... Fuel only burns at a certain rate, its the constant.
I guess I'm just asking, what are some good combinations that can be used to push more fuel, but do it for a nice clean burn...
More pop pressure results in a higher injection pressure, which means less duration, so that matched with fuel volume is going to be the single best way to tune a particular set of parts/setups... Just have to make sure you don't bump pop pressure so high for a given volume of fuel that it over pressures the pump and cuts volume...
If you have a perfectly running mechanical engine, but want to push more fuel, is it going to be better to aim for a longer injection cycle with more fine atomization, or a quickker injection cycle with more holes?
Longer durations with more volume always result in a slower burn. This can be good if you are trying to spool a big turbo, but generally leads to the fuel being burnt too late and not effectively being turned into torque. Generally you want a shorter duration, which is why you want a higher injection pressure, because the energy is released faster and more torque can be applied over the crank angle "sweet spot" by adjusting where the burn window is at...
#5
07-31-2014, 10:55 PM
What I really want to do here, is start thinking about a dual PLN injection system.
Nothing thats gonna cost 10k$.
I got the bus with the dt360, and I have my eyes out for a blown up f350.
I want to keep the stock pump, and set the timing maybe a touch over stock, like maybe 25*. No modifications, other than maybe pre-boost fuel can get opened up. I don't want to mod it so that it runs crappy.
Then, I want to put another pump, belt driven from the crankshaft on the flywheel, and plumb it on with "T"'s to the injectors. I want to set the timing on this unit to around 0* or maybe 10* of timing, not much, but should pack a punch considering it's being injected into already hot semi burned gases.
I want to adjust the secondary pump, so that all the time, it injects a touch of fuel, but not enough to even keep the engine running. This way, at idle, the injection from the primary pump at 25* or so is less, so it runs a touch quieter.
I could make a tiny throttle pull bar, and adjust the linkage to the throttle, so that the secondary pump doesn't start getting pulled until the primary is maxed out. Moving the linkage on the bar could adjust that though, making the 2nd pump come on earlier. Something to play with to make it run right, and get good fuel economy.
This isn't something that I want to put out 2000 hp, I think it could be done, and work, for a reasonable cost.
Turbochargers might be a VVT like off a dodge cummins, and a bigger 2nd turbo, whatever I can find that will work. I plan on running the VVT turbo from an electronic actuator that will be purely RPM based. Should allow spooling at any RPM, but not push for more boost based from throttle.
The plan is to see how the dt360 will hold up running at stock 2700 RPM, with more fuel and boost.
If the injection timing is significantly different, will it even need different injectors?
Thats why I was asking about the check valves, wondering if 1 pump will push fuel past the "T" on the injector, and push fuel into the other pump. Maybe a simple "T" won't work, maybe it needs check valves also.
Nothing thats gonna cost 10k$.
I got the bus with the dt360, and I have my eyes out for a blown up f350.
I want to keep the stock pump, and set the timing maybe a touch over stock, like maybe 25*. No modifications, other than maybe pre-boost fuel can get opened up. I don't want to mod it so that it runs crappy.
Then, I want to put another pump, belt driven from the crankshaft on the flywheel, and plumb it on with "T"'s to the injectors. I want to set the timing on this unit to around 0* or maybe 10* of timing, not much, but should pack a punch considering it's being injected into already hot semi burned gases.
I want to adjust the secondary pump, so that all the time, it injects a touch of fuel, but not enough to even keep the engine running. This way, at idle, the injection from the primary pump at 25* or so is less, so it runs a touch quieter.
I could make a tiny throttle pull bar, and adjust the linkage to the throttle, so that the secondary pump doesn't start getting pulled until the primary is maxed out. Moving the linkage on the bar could adjust that though, making the 2nd pump come on earlier. Something to play with to make it run right, and get good fuel economy.
This isn't something that I want to put out 2000 hp, I think it could be done, and work, for a reasonable cost.
Turbochargers might be a VVT like off a dodge cummins, and a bigger 2nd turbo, whatever I can find that will work. I plan on running the VVT turbo from an electronic actuator that will be purely RPM based. Should allow spooling at any RPM, but not push for more boost based from throttle.
The plan is to see how the dt360 will hold up running at stock 2700 RPM, with more fuel and boost.
If the injection timing is significantly different, will it even need different injectors?
Thats why I was asking about the check valves, wondering if 1 pump will push fuel past the "T" on the injector, and push fuel into the other pump. Maybe a simple "T" won't work, maybe it needs check valves also.
#6
08-01-2014, 11:39 AM
I'm also thinking; with 2 inline pumps, and "T"'s at the injector, the pressure pulses would travel back to the other pump, thus making it run as if it has oversized injection lines. So I guess even if the fuel can't flow backwards to a pump, check valves will be needed anyways, otherwise it will lope like it has big injector lines on it.
#7
08-01-2014, 11:45 AM
BTW, I bought a running dt360 bus. It's a 1993. Was hit on the side by a car, but was in service until that, so everything works and runs 100%.
I wasn't planning to start this project right now, as I'm pretty busy at work, but the right deal came along, so I jumped at it. Drove the bus 4 hours home, thing runs like brand new. Exhaust crystal clear, no haze, all fluids look great. 1100$. Other option was 3500$ down the highway for just the engine.
I know you can get 500$ junkyard dt360's sometimes, but I'll be able to harvest so many parts from the bus. Air pump is coming with the DT to the super duty lol.
I wasn't planning to start this project right now, as I'm pretty busy at work, but the right deal came along, so I jumped at it. Drove the bus 4 hours home, thing runs like brand new. Exhaust crystal clear, no haze, all fluids look great. 1100$. Other option was 3500$ down the highway for just the engine.
I know you can get 500$ junkyard dt360's sometimes, but I'll be able to harvest so many parts from the bus. Air pump is coming with the DT to the super duty lol.
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#8
08-06-2014, 07:16 PM
I'll just toss this in, for anyone else browsing...
Delivery valve concept:
Anti-dribble valve - Wikipedia, the free encyclopedia
I didn't really know what a delivery valve did before.
It's a check valve, but also upon closing, takes up a tiny bit of volume out of the high pressure line, so the injector doesn't leak.
Delivery valve concept:
Anti-dribble valve - Wikipedia, the free encyclopedia
I didn't really know what a delivery valve did before.
It's a check valve, but also upon closing, takes up a tiny bit of volume out of the high pressure line, so the injector doesn't leak.
#9
08-06-2014, 07:18 PM
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