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Stupid fuel injection question

1001001

Well Known Member
I think I understand that in an electronic fuel injection system (with direct injection at each cylinder), the fuel charge is determined by the pressure at the fuel "rail" and the duration of the opening pulse of the fuel injector. This should ensure that fuel only enters the cylinder during the appropriate part of the cycle (intake).

In a mechanical fuel injection system, such as the Airflow Performance system (which I have on the engine package for my -10), the fuel spider is pressurized at all times, but at varying pressures as determined by the fuel servo, so that the flow is determined by the differential pressure across the injector and its orifice.

What (if anything) prevents fuel from flowing during the other parts of the cycle for a given cylinder? Just differential pressure? Does this mean that fuel can flow during all cycle stages, essentially wasting fuel, even in a direct injection system?

For instance, if the fuel pressure is 20 psig (34.7 psia at sea level) (just to pull a number out of lean air) and the intake stroke pressure is, let's say, 20 inches of mercury(about 9.8 psia), we can calculate the flow of fuel through a given orifice. During the compression and power strokes, the pressure will rise well above the fuel pressure, and fuel flow through a direct injector should stop (in fact, cylinder gases should back up through the injector briefly). But when the exhaust stroke occurs, and the cylinder is essentially open to atmosphere again, we would expect a pressure of, let's say at sea level, 14.7 psia. So this would be a 20 psi differential again, and we would expect fuel to flow into the exhausting cylinder.

Does this happen? Am I missing something? Does this kind of system really waste fuel like this?

Forgive my ignorance of fuel injection for I am but a grasshopper.
 
The intake valve is there in the equation. Fuel sits in the port until the valve opens. Nothing is wasted.

EFI may or may not be timed to valve opening and the same thing applies- no fuel flows into the chamber until the valve opens.

Direct injection implies the injector is in the combustion chamber and this type involves pressure of thousands of psi generally. Fuel flow into the cylinder is independent of valve opening in this case.
 
Aircraft (gasoline) fuel injection systems are "port" injection designs. The fuel is injected into the intake tract.
Direct fuel injection systems used in some of today's cars inject fuel directly into the cylinder in a timed fashion at pressures over 2000 psi.

Cheers, David
KBTF A&P
 
Thanks for the clarification of port injection vs. direct injection. It makes sense now!

Does a mechanical fuel injection system inject at a lower rate continously, and an EFI in one big burst during the intake stroke?
 
Thanks for the clarification of port injection vs. direct injection. It makes sense now!

Does a mechanical fuel injection system inject at a lower rate continously, and an EFI in one big burst during the intake stroke?

"Constant flow" is precisely correct for Bendix style and Continental type systems; the nozzle squirts a constant stream of fuel (mixed with a small volume of air) into each intake port. The SDS and EFII brands vary pulse width (i.e. nozzle open time) to regulate fuel delivery, but that pulsed flow is also delivered continuously into each port throughout the entire four stroke cycle. Put another way, both kinds of injection flow fuel all the time, including when the intake valve is closed.
 
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"Constant flow" is precisely correct for Bendix style and Continental type systems; the nozzle squirts a constant stream of fuel (mixed with a small volume of air) into each intake port. The SDS and EFII brands vary pulse width (i.e. nozzle open time) to regulate fuel delivery, but that pulsed flow is also delivered continuously into each port throughout the entire four stroke cycle. Put another way, both kinds of injection flow fuel all the time, including when the intake valve is closed.

I might mention that port EFI systems termed "sequential" ( a misnomer IMO) may start to inject on a closed valve or open valve as the designers see fit to meet emissions, cold start or throttle response targets.
 
Dave,

Don Rivera hosts a fuel injection class at the AirFlow Performance shop twice a year, usually in November and March. I highly recommend the class. Not only does Don present the academic side of fuel injection, you spend some time in his labs with pertinent demonstrations.

It's also a good time to get your injectors balanced while you are there.

bob
 
The common terms for what Dan & Ross are describing are 'sequential', for electronic systems that time each injector's firing relative to its respective valve timing, and 'batch fire', for electronic systems that fire all (or a bank) of injectors at the same time, regardless of respective valve timing. (Not saying those are the best terms; just the common parlance.) AFAIK, all the 'off the shelf' electronic systems being marketed for homebuilt a/c are 'batch fire'.

Systems like the Megasquirt can be set up to do either method, but you'd be on your own setting one up. It has been done by individuals, though. Dan and a few others are running Megajolt systems, the ignition-only variation.
 
The intake valve is there in the equation. Fuel sits in the port until the valve opens. Nothing is wasted.

Well, 'wasted' in this case means a stoichometric mixture richer than what is required for the engine to run at the operators requirements. So yes, as we all know, mechanical systems, like carb systems, provide fuel at a "onesize fits all" ratio, with an open loop system design. EFI, allows that flow to be tuned better reducing over rich ie wasted fuel conditions mostly because of its a closed loop system. Which is why we get better fuel economy from EFI...... at the expense of introducing an electrical "component" into the system and its associated complexities......

But yes, wrt aviation systems, they all are flowing fuel constantly......just better mouse traps.
 
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Well, 'wasted' in this case means a stoichometric mixture richer than what is required for the engine to run at the operators requirements. So yes, as we all know, mechanical systems, like carb systems, provide fuel at a "onesize fits all" ratio, with an open loop system design. EFI, allows that flow to be tuned better reducing over rich ie wasted fuel conditions mostly because of its a closed loop system. Which is why we get better fuel economy from EFI...... at the expense of introducing an electrical "component" into the system and its associated complexities......

While all automotive EFI systems have used closed loop AFR control for about 30 years now, typically we are not using closed loop in aviation with leaded avgas. With a switch to unleaded, that's all possible. We already flew an RV10 back in 2007 with this technology.

The Bendix type injection works pretty well in cruise and high power with balanced nozzles actually. We see the majority of fuel savings using EFI in the start/ warmup/ taxi/ descent phases or at low power settings up high where the mechanical injection does not meter very accurately by comparison.
 
Thanks for the responses. Internal combustion engines are a bit of a hole in my thermo education.
 
Well, 'wasted' in this case means a stoichometric mixture richer than what is required for the engine to run at the operators requirements. So yes, as we all know, mechanical systems, like carb systems, provide fuel at a "onesize fits all" ratio, with an open loop system design. EFI, allows that flow to be tuned better reducing over rich ie wasted fuel conditions mostly because of its a closed loop system. Which is why we get better fuel economy from EFI...... at the expense of introducing an electrical "component" into the system and its associated complexities......

But yes, wrt aviation systems, they all are flowing fuel constantly......just better mouse traps.

My FM200 is closed loop. I have a large meat servo with its own CPU (apparently running DOS) monitoring exhaust temperature, with additional aural and tactile inputs.

Seriously, both Bendix style constant flow injection and the current electronic offerings are open loop, and there is no reason for any significant quantity of "wasted fuel" with either kind.

As Ross said, the typical constant flow system with .028" restrictors doesn't meter as well as an EFI system at low flow rates. At idle, the constant flow delivery is more dribble than squirt. Atomization is less than ideal, so vaporization is poor, thus cycle to cycle variation tends to be worse. In cruise, fuel divider accuracy drops off below roughly 6 GPH. That's not a big deal for most of us, as we tend to cruise above that, even LOP. Smaller engines can substitute .022" restrictors for an improvement. The EFI will generally deliver a smaller GAMI spread at very small fuel flows, as Dave Anders has demonstrated.

Dave, you should find all the basics in these two articles:

https://www.danhorton.net/Articles/Bendix-and-Beyond (1).pdf

https://www.danhorton.net/Articles/Fuel and Fire.pdf
 
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While all automotive EFI systems have used closed loop AFR control for about 30 years now, typically we are not using closed loop in aviation with leaded avgas. With a switch to unleaded, that's all possible. We already flew an RV10 back in 2007 with this technology.

The Bendix type injection works pretty well in cruise and high power with balanced nozzles actually. We see the majority of fuel savings using EFI in the start/ warmup/ taxi/ descent phases or at low power settings up high where the mechanical injection does not meter very accurately by comparison.

Hmm. I submit to your expert knowledge Ross, but your suby isnt O2 monitored? Guess I figured all the EFIs in aviation went the O2 route....why wouldnt they? Seems like without it, one is missing the easiest of the feedbacks available.

I yield to being schooled in aviation fuel mgmt as I'm mostly a car guy just thinking Im getting close to first flight...with Bendix inj!
 
Hmm. I submit to your expert knowledge Ross, but your suby isnt O2 monitored? Guess I figured all the EFIs in aviation went the O2 route....why wouldnt they? Seems like without it, one is missing the easiest of the feedbacks available.

I yield to being schooled in aviation fuel mgmt as I'm mostly a car guy just thinking Im getting close to first flight...with Bendix inj!

In aviation systems currently, we only monitor AFR for informational purposes to the pilot via the programmer in gauge mode, for data logging and auto mixture enrichment on some auto conversions to prevent meltdowns.

In our automotive systems, closed loop control is frequently used during cruise conditions to keep mixture near stoich automatically.

We'd love to be doing closed loop control with a wideband O2 sensor in our aviation offerings but don't feel it's reliable in the long term with leaded fuel as Mike pointed out. Hopefully Swift and Shell will change that soon with wider availability of unleaded avgas.
 
I guess this thread is sort of drifting off topic a bit, But I would love to see more development towards closed loop in the aviation ECU's. it's benefits are numerous, but I also understand the reasons it might not be a good idea.

My O2 sensor has lived for 210 hours so far on a pretty constant diet of avgas. I would like to think that it will keep going for some time ( I haven't noticed any change to its responsiveness).
My fuel map also is tuned quite lean up to 65% power or so which probably helps keep it from fouling.

Given its precision and ease of use compared to EGT, I'd be more than willing to replace a relatively cheap O2 sensor every 100 hours if necessary.


Caleb
 
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I guess this thread is sort of drifting off topic a bit, But I would love to see more development towards closed loop in the aviation ECU's. it's benefits are numerous, but I also understand the reasons it might not be a good idea.

My O2 sensor has lived for 210 hours so far on a pretty constant diet of avgas. I would like to think that it will keep going for some time ( I haven't noticed any change to its responsiveness).
My fuel map also is tuned quite lean up to 65% power or so which probably helps keep it from fouling.

Given its precision and ease of use compared to EGT, I'd be more than willing to replace a relatively cheap O2 sensor every 100 hours if necessary.


Caleb

Caleb, are you using a narrow or wide band sensor?

With W/Bs, we've seen some die in as little as 2 hours on 100LL. Conversely one long time user had over 350 on his and it was still working. All Bosch 4.9s.

We are not sure why the variation in lifespan and are talking to suppliers to see if some counterfeit ones may be leaking into the supply chain perhaps. If we can regularly get at least 150 reliably hours out of a WB, we'd implement closed loop control on aviation systems like we've offered on our automotive ones for a couple of decades now.
 
Dumb question, full of "what if's"... Keep in mind I burn a fair bit of 91 octane premium mogas (zero ethanol).

For engines like our O-360 where a 4-into-1 Cessna-style muffled exhaust is installed (with the goal of harvesting maximum cabin heat), where would a WB O2 sensor be installed? It would seem the only logical location for a summative measurement would be in the final exhaust stack, downstream from the muffler, but this is a long way from the exhaust ports on the cylinders. Just wondering, simply because when my one magneto bites the dust I'll likely end up with an SDS system of some sort replacing it.
 
Dumb question, full of "what if's"... Keep in mind I burn a fair bit of 91 octane premium mogas (zero ethanol).

For engines like our O-360 where a 4-into-1 Cessna-style muffled exhaust is installed (with the goal of harvesting maximum cabin heat), where would a WB O2 sensor be installed? It would seem the only logical location for a summative measurement would be in the final exhaust stack, downstream from the muffler, but this is a long way from the exhaust ports on the cylinders. Just wondering, simply because when my one magneto bites the dust I'll likely end up with an SDS system of some sort replacing it.

The O2 sensor needs to be at least 12 inches from atmosphere to avoid contamination from flow reversion between exhaust pulses. Hopefully that could be accomplished with your setup.
 
The O2 sensor needs to be at least 12 inches from atmosphere to avoid contamination from flow reversion between exhaust pulses. Hopefully that could be accomplished with your setup.

Hey Ross,

I've also heard conflicting stories that the O2 sensor needs to be placed fairly close to the head (within a few inches). I'm assuming that's to help keep the lead burned off. But on the other hand, I've heard that it's not healthy to have the O2 sensor subjected to a direct flame. Your thoughts?

Mark
 
Bosch says max intermittent use at 1880F and they like to see them sit below 1400F and control exact sensor temp via the internal heater.

Most naturally aspirated aircraft engines won't see 1400F down the pipe a bit so we recommend the sensors be mounted well back from the ports but more than 12 inches from the atmosphere end of the pipe.
 
Bosch says max intermittent use at 1880F and they like to see them sit below 1400F and control exact sensor temp via the internal heater.

Most naturally aspirated aircraft engines won't see 1400F down the pipe a bit so we recommend the sensors be mounted well back from the ports but more than 12 inches from the atmosphere end of the pipe.

Does the 12 inch rule also apply to junctions with other cylinders? I would imagine there would be significant backmixing between cylinders near the junctions.
 
Does the 12 inch rule also apply to junctions with other cylinders? I would imagine there would be significant backmixing between cylinders near the junctions.

No, we're mainly concerned with drawing in air from outside which makes the sensor give us a erroneous reading. Typically O2 sensors are reading an average AFR across all cylinders which is usually what we want so mixing of exhaust is encouraged.
 
The Bendix type injection works pretty well in cruise and high power with balanced nozzles actually. We see the majority of fuel savings using EFI in the start/ warmup/ taxi/ descent phases or at low power settings up high where the mechanical injection does not meter very accurately by comparison.

Ross,

I always appreciate your openness and honesty in discussing your EFI hardware and where it is beneficial relative to mechanical FI. It?s refreshing to see this honesty from a business owner in today?s marketing driven environment. :)

Skylor
 
Ross,

I always appreciate your openness and honesty in discussing your EFI hardware and where it is beneficial relative to mechanical FI. It?s refreshing to see this honesty from a business owner in today?s marketing driven environment. :)

Skylor

No point in BSing people out of their hard earned money as it will only come back at you down the road in some way. We pilots and RVers are a community of friends as far as I'm concerned and should be treated as such.

2 days ago I sent a guy over to Don at AFP because I thought mechanical injection would be a better fit for his skill set and mission.
 
Caleb, are you using a narrow or wide band sensor?

With W/Bs, we've seen some die in as little as 2 hours on 100LL. Conversely one long time user had over 350 on his and it was still working. All Bosch 4.9s.

We are not sure why the variation in lifespan and are talking to suppliers to see if some counterfeit ones may be leaking into the supply chain perhaps. If we can regularly get at least 150 reliably hours out of a WB, we'd implement closed loop control on aviation systems like we've offered on our automotive ones for a couple of decades now.

I have my Bosch wide band sensor mounted about very close to the cylinder on a single runner. I attribute its lifespan to staying in this hot and clean environment. This would be no more than a guess though. My EGT's which are measured an inch more down the stacks usually run in the 1300os or low 1400's. I also think that my tune has a lot to do with it. My engine runs very clean and lean at low power settings, and only runs rich when needed. borescope inspections show little lead build up inside the cylinders. I also would imagine the advanced timing and hotter spark at these lower settings produces a more complete burn as well.


Caleb

20170207_101436 by Caleb Lesher, on Flickr
 
There may be some correlation on the temperature and lead fouling. Maybe some other SDS users can comment on their sensor placement, EGTs and life span they've observed.
 
I have my Bosch wide band sensor mounted about very close to the cylinder on a single runner. I attribute its lifespan to staying in this hot and clean environment. This would be no more than a guess though. My EGT's which are measured an inch more down the stacks usually run in the 1300os or low 1400's. I also think that my tune has a lot to do with it. My engine runs very clean and lean at low power settings, and only runs rich when needed. borescope inspections show little lead build up inside the cylinders. I also would imagine the advanced timing and hotter spark at these lower settings produces a more complete burn as well.


Caleb

20170207_101436 by Caleb Lesher, on Flickr


Hey Caleb, I see that you have a fuel distribution block/logg mounted on your firewall and you?re not using an actual fuel rail. Have you experienced any hot fuel related issues such as vapor lock or hard starts due to not actually circulating the cold fresh fuel directly past the injectors as would be the case with a fuel rail?

Thanks,
Mark
 
O2 sensor

I mounted my O2 sensor in the junction of the four into 1 exhaust system supplied with my RV14 kit. That placed the sensor about 18? from the exit. My thought was that would average out the four cylinders for the AFR readings and comply with all the temperature requirements from the sensor manufacturer.

The sensor lasted about 100 hours. I never replaced it because once I had all the AFR?s set at 100 RPM increments I really don?t have any use for the information in the open loop configuration. I just use EGT to find peak and adjust accordingly.

Currently, my second ignition curve advances 5 degrees. I?m considering adding a -26% fuel flow increment to that advance because when I do LOP the knob position is pretty consistently -26. That would allow me to do all high power on curve one then at altitude simply switch to curve two and have no need to adjust the fuel. I believe I read that is possible with the SDS system.
 
Hey Caleb, I see that you have a fuel distribution block/logg mounted on your firewall and you?re not using an actual fuel rail. Have you experienced any hot fuel related issues such as vapor lock or hard starts due to not actually circulating the cold fresh fuel directly past the injectors as would be the case with a fuel rail?

Thanks,
Mark

Hi mark. No issues with this install that I am aware of. If I really start splitting hairs, the engine does need a little more fuel (5-10%) after a hot start for about 10 seconds. Just an observation though, definitely would not call it an issue. I'm not certain if this might be related to the longer small fuel lines I have run, or just a quirk. I choose to have my engine run and idle as lean as possible. (14:1 AFR) which It doesn't seem to like for the first 10 seconds as I described.

Caleb
 
I mounted my O2 sensor in the junction of the four into 1 exhaust system supplied with my RV14 kit. That placed the sensor about 18? from the exit. My thought was that would average out the four cylinders for the AFR readings and comply with all the temperature requirements from the sensor manufacturer.

The sensor lasted about 100 hours. I never replaced it because once I had all the AFR?s set at 100 RPM increments I really don?t have any use for the information in the open loop configuration. I just use EGT to find peak and adjust accordingly.

Currently, my second ignition curve advances 5 degrees. I?m considering adding a -26% fuel flow increment to that advance because when I do LOP the knob position is pretty consistently -26. That would allow me to do all high power on curve one then at altitude simply switch to curve two and have no need to adjust the fuel. I believe I read that is possible with the SDS system.

I took a slightly different approach. I used my EGT's to calibrate the difference in fuel flow to balance all of my cylinders. After that, I use my AFR from one cylinder as my primary mixture instrument.

Although I am comfortable with tuning via EGT, My background of tuning cars has made me a AFR fan. In my opinion it' is easier to interpret at a glance. EGT value can be effected by so many non fuel related things (ignition timing for one) that I find it too much of a moving target to work with. I was able to interface the 0-5v signal from my wideband with my GRT EFIS to display the AFR on as a gauge. This is especially useful information for data logging a flight!
 
There may be some correlation on the temperature and lead fouling. Maybe some other SDS users can comment on their sensor placement, EGTs and life span they've observed.

I mounted my O2 sensor downstream of the muffler on one side of my Vetterman crossover exhaust, so it's sampling two cylinders mixed. My peak 75% power EGT indication is ~1380*, but the exhaust stream is likely much cooler that far down the pipe. The sensor is 16" or so from the end of the pipe, IIRC.

The original sensor didn't last long at all, maybe 30 hours before it gave up. I replaced the sensor at annual last November, and added a threaded "bung extender". The new sensor is still kicking ~100 hours later, though I do feel like it's losing sensitivity in the far-rich and far-lean ranges. I'm typically running 50-80* LOP in cruise which indicates 16.3-16.7 AFR on the programmer.

I'd be interested in seeing some other users' fuel and timing maps for comparison, as I've not tweaked mine much since the initial setup. For full-power ops, I'm twisting the mixture about +15% to get 200* ROP; I think I need to do some more tweaking to the fuel maps in that regime.
 
We've been selling the extended O2 boss for about 10 months now. I can't be sure if that's helping though. One fellow had a very quick sensor failure using one but could have been other factors involved.
 
Hi mark. No issues with this install that I am aware of. If I really start splitting hairs, the engine does need a little more fuel (5-10%) after a hot start for about 10 seconds. Just an observation though, definitely would not call it an issue. I'm not certain if this might be related to the longer small fuel lines I have run, or just a quirk. I choose to have my engine run and idle as lean as possible. (14:1 AFR) which It doesn't seem to like for the first 10 seconds as I described.

Caleb

Thanks for the reply Caleb! I'm planning on setting mine up "kind of" the same....but different. LOL I'm going to design mine with an actual fuel rail on each side of the motor, but not have a full circulating system. Basically, I'm planning on having one fuel feed line that I split with a "T" or a "Y" that will then feed each rail on each side of the engine. The two injectors on each side of the engine will be tied together via one fuel line (unlike yours with individual lines) just exactly as you'd see in a fully flow through setup, except the front injector fuel line fitting on each rail will just 90* into the front injector and deadhead right there and not flow to the opposite side of the engine and then back around to the return. I want to do it this way for a couple of different reasons. The first, primarily to simplify and cleanup the plumbing. Both the fuel pumps and the fuel pressure regulator will be mounted inside the cockpit, so I'll only have one fuel line exiting the cockpit/firewall. Secondly, the type of fuel pressure regulator that I'm going to use actually has its own built in/internal fuel return port outlet. It's a three port design in that it has in/out/return ports. So, my plan is to come right out of the fuel pumps and directly into the the fuel pressure regulator, then out of the regulator to feed the the one line which will feed the two fuel rails, and then the third return line port on the regulator will then go right back to the return port on the Andair fuel selector. So this fuel pressure regulator is a little bit different in the sense that the fuel pressure is regulated as the fuel leaves regulator instead of bleeding off excess pressure as fuel returns to the regulator from the rail...or in your case the fuel distribution block/logg. So hopefully I've described my planned setup where you can visualize it and can see that mine is going to "kind of" be like yours...but different.

Mark
 
AFR

I took a slightly different approach. I used my EGT's to calibrate the difference in fuel flow to balance all of my cylinders. After that, I use my AFR from one cylinder as my primary mixture instrument.

Although I am comfortable with tuning via EGT, My background of tuning cars has made me a AFR fan. In my opinion it' is easier to interpret at a glance. EGT value can be effected by so many non fuel related things (ignition timing for one) that I find it too much of a moving target to work with. I was able to interface the 0-5v signal from my wideband with my GRT EFIS to display the AFR on as a gauge. This is especially useful information for data logging a flight!

I can see why you would go this route.

My engine from the factory had a GAMI spread of about 0.5 gallons per hour. I have been using the individual fuel trim feature to reduce that spread for each long flight. What I do is find peak EGT then go either ROP or LOP and use the cylinder trim to adjust the delta of the other three cylinders. In other words, for ROP I use the first cylinder to peak as the reference for 100ROP and then adjust the other three cylinders for 100. For LOP I use the last cylinder to peak then adjust to -25LOP (or any value I want for the day) then use the cylinder trim to adjust the other three. The engine runs extremely smooth this way; however, the percent change per cylinder does vary for ROP and LOP. At this point I?m uncertain that the variance is significant or should I simply use an average number. The mechanical injection systems must use an average adjustment.

Here is where your method may be more intuitive. When I set LOP and then advance the ignition the delta LOP number calculated on my G3X change significantly. I decided that since my fuel flow was constant the numbers were inacurate due to the ignition change. With your method of using AFR I would have a better understanding.

Would you be willing to run a simple test flight?

1) Set a particular LOP cruise condition, say 25LOP. Write down your ignition BTDC, LOP, fuel flow, and AFR.
2) Advance your ignition to your normal LOP advance. Write down your ignition BTDC, LOP, fuel flow, and AFR.

My guess is that the fuel flow and AFR will remain relatively constant, but the LOP numbers with change and will be invalid. That appears to be what I see on my system. If you do not have time to run this test, I could just reinstall my O2 sensor.
 
I can see why you would go this route.

My engine from the factory had a GAMI spread of about 0.5 gallons per hour. I have been using the individual fuel trim feature to reduce that spread for each long flight. What I do is find peak EGT then go either ROP or LOP and use the cylinder trim to adjust the delta of the other three cylinders. In other words, for ROP I use the first cylinder to peak as the reference for 100ROP and then adjust the other three cylinders for 100. For LOP I use the last cylinder to peak then adjust to -25LOP (or any value I want for the day) then use the cylinder trim to adjust the other three. The engine runs extremely smooth this way; however, the percent change per cylinder does vary for ROP and LOP. At this point I?m uncertain that the variance is significant or should I simply use an average number. The mechanical injection systems must use an average adjustment.

Here is where your method may be more intuitive. When I set LOP and then advance the ignition the delta LOP number calculated on my G3X change significantly. I decided that since my fuel flow was constant the numbers were inacurate due to the ignition change. With your method of using AFR I would have a better understanding.

Would you be willing to run a simple test flight?

1) Set a particular LOP cruise condition, say 25LOP. Write down your ignition BTDC, LOP, fuel flow, and AFR.
2) Advance your ignition to your normal LOP advance. Write down your ignition BTDC, LOP, fuel flow, and AFR.

My guess is that the fuel flow and AFR will remain relatively constant, but the LOP numbers with change and will be invalid. That appears to be what I see on my system. If you do not have time to run this test, I could just reinstall my O2 sensor.


I'd be happy to do some test flying and comparisons... just as soon as the weather will allow. The smoke from all the wildfires here in northern CA has been pretty bad lately. I have a feeling that the garmin efis is accounting for the change in % power based on being ROP vs LOP. My GRT system only accounts for altitude, MP, and RPM. This would lead my "65%" cruise to actually being much lower when I pull to LOP.

Caleb
 
Here is where your method may be more intuitive. When I set LOP and then advance the ignition the delta LOP number calculated on my G3X change significantly. I decided that since my fuel flow was constant the numbers were inacurate due to the ignition change. With your method of using AFR I would have a better understanding.

Would you be willing to run a simple test flight?

I run a megasquirt based EI in my 6 and also have two switchable ignition maps. I also see the change in EGT that correlates with the table switch.

When you change your ignition advance, you are moving the timing of peak pressure in your cylinders. As you move towards your engine's optimal peak pressure timing, your CHTs will rise and your EGTs will fall (more heat is remaining in the cylinder and used to create torque). As you move away from optimal, the opposite happens.

Whenever you change timing, you need to re-find your peak EGT if you are looking to be a specific # of degrees LOP.

This is loose definition and optimal isn't necessarily safe or recommended.

Larry
 
I run a megasquirt based EI in my 6 and also have two switchable ignition maps. I also see the change in EGT that correlates with the table switch.

When you change your ignition advance, you are moving the timing of peak pressure in your cylinders. As you move towards your engine's optimal peak pressure timing, your CHTs will rise and your EGTs will fall (more heat is remaining in the cylinder and used to create torque). As you move away from optimal, the opposite happens.

Whenever you change timing, you need to re-find your peak EGT if you are looking to be a specific # of degrees LOP.

This is loose definition and optimal isn't necessarily safe or recommended.

Larry

Larry, I'm very interested in your setup! I've built 3+ Megasquirt units for fuel injected cars and trucks and really like the software. Is there a place with more information or photos?

Also, completely agree with you on EGT/CHT relationships

Caleb
 
+1! I've thought about using a mega/micro squirt for years, but I've been too lazy to install the injectors and a bit leery about dialing in the fuel & ignition maps for a Lyc. I'd be grateful for any info, pics, etc you can share.

Charlie
 
Larry, I'm very interested in your setup! I've built 3+ Megasquirt units for fuel injected cars and trucks and really like the software. Is there a place with more information or photos?

Also, completely agree with you on EGT/CHT relationships

Caleb

I am not sure I have any interesting photos. I built a MS EFII for my porsche 911 when I added the turbo and I really liked it. At this time, I am only using it for ignition in the 320. I had considered going to full EFII, but didn't want the risk and hassle of putting a second one in for redundancy, as well as another battery.

I made a custom pickup device that goes in the mag hole and uses a standard mag gear and leverages a hall effect sensor. I actually made two of them and planned to sell the other, but didn't get any interest. I have the old generator flywheel with the small pulley and there is just not enough room to shoe horn in a pickup for magnets on the flywheel.

The MS has two ignition maps that are switchable with a toggle. I also wired a second switch into the knock sensor circuit. This switch allows me to drop 5* (programmable) from either map by flipping the toggle. I use this in climb to help control CHTs in summer, as they run higher since installing the cowl exit fairing.

I have around 500 hours on this setup and never had a hiccup. I use autolite 386 (can't remember the number at the moment - 18mm w/resistor plug.

I plan to put two MS units in the 540 I am building for my 10 (It will have redundant electrical system). I wanted to play with the megajolt (I REALLY like their ability to move the advance with a rheostat), but don't know where to mount a toothed wheel (the EDIS requires a VR sensor). It will be much harder to make mag pickups, as the mags on the 540 turn at 1.5:1 instead of 1:1 like the 320.

I had considered doing the fuel with the MS on the 10, but there just isn't enough advantage over the bendix to make it worthwhile. Possibly it is a step backwards, as there is no individual injector fuel trim like the SDS has. These Lycomings have such poor air distribution that this is required for maximum fuel efficiency in cruise.

I'll PM you my number. Feel free to call me to discuss further.

Larry
 
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+1! I've thought about using a mega/micro squirt for years, but I've been too lazy to install the injectors and a bit leery about dialing in the fuel & ignition maps for a Lyc. I'd be grateful for any info, pics, etc you can share.

Charlie

There is a lot to getting the fuel map dialed in Charlie. It took me quite a while to get it right on the porsche, especially for cold starts (you only get one or two chances per day to test it) and the jumps get very sharp at the lower temps. That said, the Lyc should be a lot simpler as you don't have to worry as much about acceleration profiles and the usable profile on the map is smaller. They have a tool to give you the initial basic map based upon displacement and it is close enough to get the engine started. You need a WB O2 sensor and gauge to do this.

The ignition map was very simple to dial in on the 320. Porsche was a bit tougher, but that was because of the 10#'s of boost.

You would need IAT sensor plumbed in and possibly at throttle body. However, I believe the MS will work without a TPS, though I don't know how much performance or throttle response suffers as I didn't try it.
 
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Thanks for the reply Caleb! I'm planning on setting mine up "kind of" the same....but different. LOL I'm going to design mine with an actual fuel rail on each side of the motor, but not have a full circulating system. Basically, I'm planning on having one fuel feed line that I split with a "T" or a "Y" that will then feed each rail on each side of the engine. The two injectors on each side of the engine will be tied together via one fuel line (unlike yours with individual lines) just exactly as you'd see in a fully flow through setup, except the front injector fuel line fitting on each rail will just 90* into the front injector and deadhead right there and not flow to the opposite side of the engine and then back around to the return. I want to do it this way for a couple of different reasons. The first, primarily to simplify and cleanup the plumbing. Both the fuel pumps and the fuel pressure regulator will be mounted inside the cockpit, so I'll only have one fuel line exiting the cockpit/firewall. Secondly, the type of fuel pressure regulator that I'm going to use actually has its own built in/internal fuel return port outlet. It's a three port design in that it has in/out/return ports. So, my plan is to come right out of the fuel pumps and directly into the the fuel pressure regulator, then out of the regulator to feed the the one line which will feed the two fuel rails, and then the third return line port on the regulator will then go right back to the return port on the Andair fuel selector. So this fuel pressure regulator is a little bit different in the sense that the fuel pressure is regulated as the fuel leaves regulator instead of bleeding off excess pressure as fuel returns to the regulator from the rail...or in your case the fuel distribution block/logg. So hopefully I've described my planned setup where you can visualize it and can see that mine is going to "kind of" be like yours...but different.

Mark

Mark33;
I saw something like that in another post months ago and looked it up on Summit racing. What FP regulator are you using?
 
Hey John,

I?m using the MagnaFuel (part number MP-9925-B). I think Jegs or Summet has the best price on them. Oh, one other thing, there?s no vacuum control line needed for these. I actually called MagnaFuel and spoke with them about this. I told them that the only fuel pressure regulators that I?d ever dealt with had a vacuum line port on it so that proper fuel pressure could be maintained in relation to MAP. They said that this particular regulator is designed with an internal spring and diaphragm mechanism that maintains the desired fuel pressure and they assured me that a vacuum line wasn't needed to maintain the constant desired pressure regardless of throttle position.

Mark
 
Hey John,

I?m using the MagnaFuel (part number MP-9925-B). I think Jegs or Summet has the best price on them. Oh, one other thing, there?s no vacuum control line needed for these. I actually called MagnaFuel and spoke with them about this. I told them that the only fuel pressure regulators that I?d ever dealt with had a vacuum line port on it so that proper fuel pressure could be maintained in relation to MAP. They said that this particular regulator is designed with an internal spring and diaphragm mechanism that maintains the desired fuel pressure and they assured me that a vacuum line wasn't needed to maintain the constant desired pressure regardless of throttle position.

Mark

On a mechanical regulator, you must have MAP reference to maintain a constant pressure differential above MAP. You could run without map reference but it will make programming the system more time consuming as that variable is not constant.

Pretty much all the auto OEMs used MAP reference on their mechanical regulators.
 
On a mechanical regulator, you must have MAP reference to maintain a constant pressure differential above MAP. You could run without map reference but it will make programming the system more time consuming as that variable is not constant.

Pretty much all the auto OEMs used MAP reference on their mechanical regulators.

Ross,

Yeah, that's exactly what I thought, but according to MagnaFuel a vacuum reference isn't necessary. There is port on the side of the regulator that can be used as either a "boost" port or just a filter port. I guess the boost port could be tied into the MAP vacuum source. The only thing I can think of is that the way it's designed with its internal return and the return port on the regulator being the actual return going back to the tank rather than being the return from the fuel rail back into the regulator. Where am I going wrong here?

Mark
 
Ross,

Yeah, that's exactly what I thought, but according to MagnaFuel a vacuum reference isn't necessary. There is port on the side of the regulator that can be used as either a "boost" port or just a filter port. I guess the boost port could be tied into the MAP vacuum source. The only thing I can think of is that the way it's designed with its internal return and the return port on the regulator being the actual return going back to the tank rather than being the return from the fuel rail back into the regulator. Where am I going wrong here?

Mark

The manufacturer is talking about gauge pressure with respect to atmosphere. Ross is talking about gauge pressure with respect to the manifold. The electronic SDS/EFII style injectors are seeing the pressure delta from the fuel side to the manifold, and need that pressure delta to be constant. For that to happen, you must supply a MAP reference to the regulator. If you are using mechanical servo injection, then it doesn't matter.

Example - if you have 40 psig delta at idle with the electronic injectors, then when you open the throttle fully you will only have about 30 psig unless the fuel pressure rises the same amount as the MAP rises. The electronic injectors operate only by pulse width and number of pulses - which requires a constant delta across the injector face - which requires the fuel pressure (with respect to atmosphere) to change so that the fuel pressure (with respect to MAP) does not change.
 
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Ross,

Yeah, that's exactly what I thought, but according to MagnaFuel a vacuum reference isn't necessary. There is port on the side of the regulator that can be used as either a "boost" port or just a filter port. I guess the boost port could be tied into the MAP vacuum source. The only thing I can think of is that the way it's designed with its internal return and the return port on the regulator being the actual return going back to the tank rather than being the return from the fuel rail back into the regulator. Where am I going wrong here?

Mark

The way fuel is returned from the regulator has no impact on whether it provides a constant differential above MAP. I haven't seen a reg which has a port for boost reference that doubles as a filter location since these should be separated by the diaphragm.

Virtually any reg I've worked with that has a "vacuum" port can also use that port as boost reference. In other words, fuel pressure is reduced below spring pressure when vacuum is on the port and raised above spring pressure when boost is applied there.

I'm thinking the guys telling you this stuff don't understand how these things work perhaps or don't understand how not using MAP reference would impact tuning an EFI system.
 
The manufacturer is talking about gauge pressure with respect to atmosphere. Ross is talking about gauge pressure with respect to the manifold. The electronic SDS/EFII style injectors are seeing the pressure delta from the fuel side to the manifold, and need that pressure delta to be constant. For that to happen, you must supply a MAP reference to the regulator. If you are using mechanical servo injection, then it doesn't matter.

Example - if you have 40 psig delta at idle with the electronic injectors, then when you open the throttle fully you will only have about 30 psig unless the fuel pressure rises the same amount as the MAP rises. The electronic injectors operate only by pulse width and number of pulses - which requires a constant delta across the injector face - which requires the fuel pressure (with respect to atmosphere) to change so that the fuel pressure (with respect to MAP) does not change.

That would make sense. With there being a "vent" port on the regulator I can see where it would be sensing atmospheric pressures and not MAP. I guess the way I understood it as the manufacturer was explaining it to me is that the regulator would maintain the desired/dialed in rail pressure based on internal regulator spring pressure rather than on a diaphragm that required MAP to keep the rail pressures constant. So, I guess it's back to the drawing board with regards to my plumbing plan. LOL!!

This next question may be aimed a little more at Ross and the Borla regulator he uses. In the Borla reference material it specifically says to install the regulator on the downstream/return side of the fuel rail. So, the question is, is it acceptable to have everything (fuel supply from pumps, fuel rail distribution lines, and fuel pressure regulator) all plumbed into a single fuel log/distribution block?

Mark
 
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