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User avatar
By bruceme
#37318
I'm going to try to use the speeduino on the homebuilt RV-4 two person light aircraft I built.

Image

Before you hit reply to say "! DO NOT USE THIS ON AN AIRCRAFT !" I have a fully redundant ignition and fuel system. Aircraft engines already have two electrically independent ignition systems (they have always been unreliable, that's not a new thing) I will not remove one of the existing magnetos. The fuel backup is a 3-gallon-gravity-fed TBI from a manual valve in the cockpit. So this engine will continue to run (a little rougher), even with the electrical master switch off.

The engine that currently powers this aircraft is a mechanically injected Lycoming IO-320 of 160 rated horse power at 2700 RPM. It is air-cooled, horizontally opposed, 4-cylinder, normally aspirated of 320 cubic inch displacement. I am running a dual Garmin G3X Electronic Flight Instrumentation System (EFIS) with integrated Engine Monitoring System (EMS). That means all four cylinders are monitoring exhaust and cylinder head temp and I also have oil temperature (think H20 for air cooled), oil pressure, MAP, outside air temp, fuel pressure, fuel flow and tach.

Image

I'm doing this project to achieve two goals;

- Efficiency; Far better dynamic fuel balancing from mass-flow-trimmed sequential fuel injection. The induction system is very imbalanced, and it is difficult to statically trim injectors. Also, dynamic spark advance is another 5% improvement in BSFC.
- Better and safer starts (especially hot)
- Simpler pilot operation (no mixture knob to manage or leave too lean/rich by accident)
- Better, cleaner, correctly-operating (detonation/pre-ignition) as the engine will always operating at ideal fuel/air mixture for the requested MAF/HP.

Non-goals:
- Speed/Power (it is what it is, I'm not a power wonk)
- Science project... not the place for it. Needs to just work
- Save money

My background... I'm a software engineer by trade. I have built a lot of cool stuff (like airplanes) and I enjoy DIY electronics. Not affraid of a transistor or a solder iron.

All that said... I've done a lot of research and I have questions....

1 - I need way to trim the injectors sequences in flight. Something really simple, maybe bluetooth to my phone even. I won't have to do this very often, but testing and long X/C, I'll want to tweak it while I'm flying.

2 - From clicking around Tune Studio, I have little confidence I can do an adequate job of getting a reasonable base map. Is there anyone here that might be able to help?

I have started a github on this project for me to collect my thoughts as well...

https://github.com/bruceme/aerosquirt/wiki

Thank you and I do look forward to feedback,

-Bruce
User avatar
By PSIG
#37326
Welcome, Bruce. You are not the first aviation application by a few here. ;)
bruceme wrote:
Sat Aug 24, 2019 5:56 pm
1 - I need way to trim the injectors sequences in flight. Something really simple, maybe bluetooth to my phone even. I won't have to do this very often, but testing and long X/C, I'll want to tweak it while I'm flying.
Clarify for us - are you after actual injection sequence changes (1-2-3-4 vs 1-3-4-2, etc), or individual cylinder fuel flow trim (ICFT) changes, or injection end-point angle changes, or … ?
bruceme wrote:
Sat Aug 24, 2019 5:56 pm
2 - From clicking around Tune Studio, I have little confidence I can do an adequate job of getting a reasonable base map. Is there anyone here that might be able to help?
The general VE Table generators are designed for more typical automotive applications, and will likely have an aneurysm creating a starting table for your application. Alternatives are some calculated or well-guessed "wedge" tables, or seed a table with reasonable calculated VE values using accepted methods such as this, or an online calculator such as this. Then use the tools in TunerStudio to interpolate and blend to get a starting table that is close enough to get it running. Tune from there. You have the benefit of lots of published data and a running engine to pull data from.

David

I don't know your engine's spec's, but this would be a random example of finding a value for one of the VE cells in your starting table:
ATG_VE_calc.png
ATG_VE_calc.png (55.19 KiB) Viewed 2564 times
User avatar
By bruceme
#37336
That was an awesome response! Thanks David.

I am entirely focus on trimming. Shaping and exact sequencing are irrelevant. Today, the mechanical injector does a great job just dumping raw fuel with no real spray or pattern 100% of the time into the intake plenum right behind the valve. I get very nearly ideal lean-of-peak specific fuel consumption from that, if it was balanced. The balancing bit is the whole game.

the EFI injectors I intend to use are Harley or Mercruiser injectors, which are suggested for up to 86hp / cylinder.

Mercruiser 861260T Mallory 9-33101

Image

They produce about 300-550cc, depending on PSI, and they not shaped. I have a local shop CnC'g the custom injector bosses from aluminum which will screw into the top of the jug like to the current injectors.

This is a cylinder before the injector port was drilled and tapped... it's the flat spot behind the fuel tube going nowhere.

Image

... On the starting front and VE table side. Yeah, I really hope someone has a table I can start from :) The engine is very similar in RPM/jug to a Harley... but timing is way way different. As for starting; right now it's pilots discretion... which means we squirt and pray. I think there's a lot of room for improvement there. These engines (with their current accessories) are dinosaurs; but the bones are solid and for powering a a light airplane, you just can't do any better.
User avatar
By bruceme
#37337
Some more background on traditional aircraft starting...

The magnetos on aircraft use an "impulse coupler" to both retard and "snap" the magneto coil to give a "more powerful" (still very weak by any standard) and retarded starting spark. Once the engine goes above about 500rpm, the retarding arm centrifugally retracts and it turns into a normal magneto with 25 degrees of advance.

In general these engines start very easily and predictably (1 or 2 blades) when you do it right. These are my "best practice" manual procedure for starting any aircraft engine.

Normal first start (70F) - You need about 40cc (2 tablespoons) of priming fuel. My engine is injected, so this means you turn the electric pump on and open the mixture for 3-6 seconds... I can hear the "girgle" when the fuel hits the port, that's perfect! Carburetor engines have both an accelerator pump (pump the throttle) and a manual priming pump (syringe-style) that dumps raw fuel to the same place my injectors go, but only on one cylinder, not all four. Typically you'd do 2 squirts of the prime pump to get the same effect.

So now there's fuel in the port, I like to (with the mags grounded/off) hand-prop so I can gauge compression on all four cylinders and mix the fuel into the cylinders so they're loaded and ready to go. Then I get in the plane, unground the mags hot, then engage the starter. If you do this, it will start on the very first blade every time, garenteed.

Colder starts... bellow 40F, the engine must be pre-heated, you need more priming fuel up to 160cc or 6 squirts of prime. Same procedure and it may take a few blade rotations to get the cold air to mix with the fuel.

Hot starts... the reality of a hotstart for all mechanically fuel injected engines is nightmarish because gravity dumps all that fuel into intakes and you have a flooded engine start, which is awful. I'll skip that and instead talk about a carburated hot-start technique I use on airplanes that frequently shut-down like tow-planes. Go up... come down, 20 min, shut down and wait 20 minutes to go again.... repeat x15 in a day. This is the technique I use for this aircraft.

The key to a good hot-start is actually the shut down... Leave the engine at a good idle (1100 rpm) don't touch any knobs, ground the mags/off to turn the engine off. Now the engine stopped with a good charge of fuel/air hanging out in all four cylinders... it's a loaded gun ready to fire. Un-ground the mags/hot and you can take that blade through the next impulse-coupler [click] and BANG! It _WILL_ start every time like a sewing machine.

So EFI hot starts... normal warm-engine fuel/air mixture, crank the prop fire the ignition.

Maybe this helps... It's basically are really big lawn mower engine :)
By LAV1000
#37340
Those injectors are magneti marelli ones and there is mostly an iwp number on the connector.
At least over here in Europe.
User avatar
By PSIG
#37343
Contemplating for a moment; an equivalent of each of your starting scenarios may be accomplished with Speeduino. Note your method of priming/hand-propping/cranking also provides a longer dwell period for the fuel to additionally vaporize in the cold engine. Without that fuel dwell time more priming would generally be required — and there are limits. Sometimes a few moments of patience is much more effective than more fuel and a quick crank.

I recall one Kitfox with a Subaru (electronic) where the owner developed a starting technique for a failed starter after needing it, and had no locking brakes. :shock: What he did was to prime and hand-prop 3-blades to the center of compression (just past ignition point), with a blade at about 10 o'clock. Then he would get in the cockpit and while holding brakes in a very awkward way would switch-on ignition, and stretch out the open door to just brush the prop backwards with his fingertips. It would hit ignition point, fire spark, and light-off in correct direction every time. Necessity is the Mother …

+1 to LAV1000, as those appear to be the stubby little MM/Weber injectors commonly known as "Pico".

David
User avatar
By bruceme
#37368
At peak power, these engines traditionally used excessive fuel to cool the heads. We call it "rich of peak". We intentionally run it on the rich side. So let's say I take-off at a 9:1 air/fuel ratio... Then once you level off in cruise, you reduce power to 75% and leans the mixture control until you hit the first cylinder that "peaks" EGT. Here a pilot has two choices;

1 - Turn the mixture knob back in and go "Rich of peak" by 50F as a rule of thumb. Let's say this AR is 11:1. It is considered by most pilots to be "safest" as you are running the engine with ample fuel and no one cylinder is falling off the "lean" peak which causes the engine to run rough. Carbureted engines are so imbalanced, they only have this option.

2 - Turn the mixture knob even leaner by 50F. This can only be done if you very tight AR balance and it's likely very close to 14. On a well balanced engine, you can lean and lean and it just makes less and less power. It doesn't run rough. Running lean of peak (LoP) is a significant fuel savings for cross-country. It means the difference between 7gph and 5gph at cruise speeds.

So my question is this... How should I handle these fuel modes? Should there be a hard split at some arbitrary RPM like 2550 (2700 rpm is full power) where it dramatically knotches from rich of peak to lean of peak?

- You don't want to "hang out" at peak EGT, it generates heat... Air cooled engines don't like heat. Increases ware and effects time to overhaul.
- Detonation or pre-ignition at power settings below 75% will not damage these engines (they're built like brick shitters). 2500rpm is about where that is at sea-level (it's higher at higher altitudes, less MAP).
- I want to avoid anything pilot switches for "go lean" as we tend to forget them and shove the throttle forward not paying attention.

How is this handled in efficient cars? Is a knock sensor the missing ingredient here? So just use a good AR and let the knock sensor detect detonation/pre-ignition and "knock it off" even at high power settings?


Thanks!
User avatar
By PSIG
#37372
bruceme wrote:
Tue Aug 27, 2019 11:58 am
At peak power, these engines traditionally used excessive fuel to cool the heads. We call it "rich of peak". We intentionally run it on the rich side. So let's say I take-off at a 9:1 air/fuel ratio... Then once you level off in cruise, you reduce power to 75% and leans the mixture control until you hit the first cylinder that "peaks" EGT. Here a pilot has two choices;

So my question is this... How should I handle these fuel modes? Should there be a hard split at some arbitrary RPM like 2550 (2700 rpm is full power) where it dramatically knotches from rich of peak to lean of peak?
This would generally be handled in basic tuning, in order to see the typical effects at the usual rpm and MAP. If you can (and want) lean at <2500, and the engine tolerates that well (including with optimized ignition timing, which relatively reduces heat), then tune to do that. While it may be possible to be configured for some compensations of hot 'n high effects or the alternatives, a "mixture and timing" knob of sorts could perhaps be implemented to give the PIC a means of altering for unusual conditions. One example could be using the Flex Fuel input, which can alter both fueling and ignition timing as a variable. Perhaps also using a (slightly) irritating green LED to remind you to set it back when appropriate.
bruceme wrote:
Tue Aug 27, 2019 11:58 am
How is this handled in efficient cars? Is a knock sensor the missing ingredient here? So just use a good AR and let the knock sensor detect detonation/pre-ignition and "knock it off" even at high power settings?
How do you detect or avoid detonation or pre-ignition now? Generally, detonation and the pre-ignition it promotes are avoided in other engine types by using sufficient fuel grade and tuning to simply not permit favorable conditions for det and pre-ig. Again, for unusual conditions, a knob could be employed to extract it from those conditions. This is all founded on good theory, but is only that, and is entirely up to you and your choices to use, apply or not apply any information or crazy ideas. These are not suggestions for you and only theories and hypotheses of how certain actions could perhaps be performed if anyone was crazy enough to actually try it.

David
By LPG2CV
#37373
WUE could be attached to a variable resistor (takes the place of the coolant temp sensor). The WUE slope could be used to do what ever you want (add or subtract fuel). The adjustment would be across the MAP/REVS range. Plus the irritating led of course. A clever person could have green/red for rich/lean. And/Or a range on the dash board
User avatar
By bruceme
#37518
PSIG wrote:
Tue Aug 27, 2019 8:22 pm
How do you detect or avoid detonation or pre-ignition now? Generally, detonation and the pre-ignition it promotes are avoided in other engine types by using sufficient fuel grade and tuning to simply not permit favorable conditions for det and pre-ig.
Exactly how it's done. General aviation's go-to fuel is 100-LowLead (100LL), it's usually 2-3x more $/g(it's 4-6 right now), pre-stabalized, 100 octain and the "low lead" is relative term to 1940's fuel which was loaded. It's something like 3x the lead of 1980's unleaded. So yes, we generally run too rich and too high an octain for it to happen. Traditional aircraft engines are fixed ignition, so overloading it with high octain high lead fuel was the only option. The high mixture rates and high levels of lead mean spark plug and valve fowling... another reason I want to go EFI.
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