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How does the mg in the Torque Based Fuel Map relate to Inj. Volume (mm3) in the Injection Quantity to Pulsewidth Map?
Tuning my 7.3L the PW Map was mg vs icp and is pretty simple. I'm just trying to figure out if I can adjust the PW's with the Torque Based Fuel Map. I've messed with the PW Map a little but it seems like it changed the torque calculations and Fuel Milage Readout in the dash.
So basically a pedal position is converted to a torque number using the pedal map. The torque value and rpms are used to come up with a fuel mass (mg). This along with the current fuel rail pressure (psi or kpa) goes into the pulse width map to come up with a desired IPW (us or ms)Quote:
Originally Posted by bstroked
I recommend if you want to add peak power, increase duration of the IPW map only at the highest fuel mass columns such as 120 and more. If you want more overall power at partial throttle, increase the pedal to torque map. This will also increase the boost, timing and shift pressure and keep everything in sync. If you just want to add more fuel, then try increasing the torque to fuel map. Keep in mind though, this may increase smoke levels or increase Regen frequency.
So the columns in the
Inj. Volume MAP are mg of mass fuel? I'm trying to tune more for MPG, so am wanting to make a little more torque in the midrange cruising area.... How I got it with my 7.3L was lengthen the PW out and lower Inj psi to keep the fire burning a little after TDC...
Not sure how that helped you before. Typically you will get more mpg by having as much fuel burn at tdc as possible. This is done by running a bit more injection pressure to shorten duration and keep the timing slightly advanced so combustion starts right before TDC
It uses leverage to create torque.... I've found that it's hard to tune the big bang way,because you have to get it about perfect... Plus there's all kinds of variables that effect when it actually combusts....
In my head this is what i picture, lol. The higher pressure shorter PW to be like a guy running up and jump kicking a shopping cart, and the lower pressure higher PW to be a guy running up and pushing the cart. I think timing plays a huge roll in how well each way works obviously but that's how i see it lol. I'm very new to all this but i'm curious if you'd add more timing to the longer PW compared to the shorter PW with higher pressure to get the same power? I'd think the higher PW would make more TQ and the shoter PW would make more HP. Or am i completely wrong on this? IDK but i like the idea of trying them both out and seeing. Anyone else have any good data on this topic?
You don't actually command a specified pulse width. That is decided by the ECU based on the current rail pressure and desired fuel mass. By commanding higher RP you will end up with lower PW to reach the same fuel mass. The reason higher pressure results in more power is the combustion can be centered around top dead center more precisely. It also results in a more complete fast burn so there is less time for the cylinder walls and piston to absorb the heat. No matter where the fuel combusts, if it is the same amount of fuel the pressure will be elevated similarly throughout the piston traveling down.Quote:
Originally Posted by JaegerWrenching
Ahh that makes sense, because in the gas world we have solid fuel pressure for the most part so we are allowed to control injector pw. So fuel mass is essentially the same as commanding a certain pw to get or maintain X Lambda but how do we know we are at X lambda in the diesel world? By monitoring EGT's?Quote:
Originally Posted by CKrueg
Since diesels are compression ignition the AFR is not critical for combustion. It can vary from over 50 under very low loads to less than 10 (this will result in smoke). Stoichiometric ratio is about 15 and peak power with a complete combustion will be made slightly leaner than this. Egt can be a good indicator or AFR along with smoke. High egts and smoke result from to much fuel. In a gasoline engine they are air throttled- that is driver demand results in a certain amount of air mass and the ECU will deliver the right fuel mass to meet a given AFR. In a diesel (at least the 6.7) the driver demands a certain torque value and it is converted to a fuel mass. The airflow is a result of the rpms, vgt, ambient air etc... I believe the 6.7 uses a MAF to estimate lambda and there is a few limiting tables that will cut the fuel back to prevent smoke until the air flow can increase.Quote:
Originally Posted by JaegerWrenching
[QUOTE=CKrueg;560553]Since diesels are compression ignition the AFR is not critical for combustion. It can vary from over 50 under very low loads to less than 10 (this will result in smoke). Stoichiometric ratio is about 15 and peak power with a complete combustion will be made slightly leaner than this. Egt can be a good indicator or AFR along with smoke. High egts and smoke result from to much fuel. In a gasoline engine they are air throttled- that is driver demand results in a certain amount of air mass and the ECU will deliver the right fuel mass to meet a given AFR. In a diesel (at least the 6.7) the driver demands a certain torque value and it is converted to a fuel mass. The airflow is a result of the rpms, vgt, ambient air etc... I believe the 6.7 uses a MAF to estimate lambda and there is a few limiting tables that will cut the fuel back to prevent smoke until the air flow can increase.[/QUOTE ]
Thank you, great explanation! I drive my truck and i can see it makes boost but doesn't always feel fast for the amount of boost it was making. This just now made sense as to why i can be cruising at 20psi, the truck is nice, tame and smooth. But i can tip in and it instantly rolls out! Like no boost delay! That's so weird to me because in the gas world boost or kpa is how we base all fueling. But in these diesels it only means the boost is there. We don't have to fuel for it if we don't want, i really like that idea lol!
[QUOTE=JaegerWrenching;560615]Yep that is why boost doesn't always correspond with your power output. However you are wasting energy pumping excess air. The only benefit to making boost like that is like you said, to increase response.Quote:
Originally Posted by CKrueg