EFI for small industrial engine--aircraft use
Posted: Sun May 17, 2020 12:14 am
Greetings. I've just started pawing through the materials in this forum and the DIYEFI.org site, lots of great material, much of it over my head. I'm hoping to get opinions on whether FREE EMS may be right for my application.
I'm hoping to find/build an EFI system suitable for fitting to small (25-35 HP) V-twin industrial engines that are increasing popular in very small experimental aircraft. Most folks flying them are using carburetors, often the inexpensive ones from the OEMs. These can be fussy, and I think we can maybe do better.
The single most important attribute is reliability. Next is reliability. Ease of use and in setting it up will also be important. Fuel efficiency would be very welcome, but is less critical than remaining airborne. Low cost is desirable (the engines themselves cost approx $1000 new)
Megasquirt/Microsquirt could surely be made to work, but my impression is that the code is immense, not entirely transparent, and the cost isn't especially low. The problem (IMO) with huge software, which probably does a lot of great things across a wide variety of users, is that in this application it makes it hard to anticipate failure modes. I (think) I'd do best with the minimal number of sensors and rock-solid defaults that can be put in for any of them so the engine continues to chug along at sufficient output to remain safely airborne.
Attributes of this application:
-- Open loop is desirable, but closed loop might be acceptable if it proves best for other reasons. The most common fuel for general aviation in much of the world ("100LL") still contains tetraethyl lead. Lambda sensors don't like it. Still, users of these engines might be willing to take their own unleaded gasoline to the airport for local flying, if this proves to be the best way.
-- The uneven induction pattern of the V-twin engines requires separate induction and exhaust circuits for each cylinder. So, two injectors.
-- Contrary to automobile use, a smooth idle isn't very important, power settings are fairly constant and generally high. Air temperature and density will vary. Any "limp home" mode must prioritize adequate power output over preservation of the engine.
-- Users are generally willing to make adjustments in flight. They are used to carburetors requiring manual mixture adjustments, etc. CHT and EGT readouts for each cylinder will be available in the cockpit.
-- Power available: These engines generally have 16A alternators for the 12V electrical system, so about 200 watts produced. If we subtract other required power uses and a desire to avoid overtaxing the charging system, it would be best if we could limit the EFI to about 100 watts, if that is feasible.
-- Injection timing: not especially critical, especially if we can do away with an RPM input in the bargain (one less failure point). Squirt the fuel into the runner at the right rate and it'll get into the jug when air flows. Too cavalier?
-- The engines are air cooled, so there's no coolant temperature to monitor (though CHT is available).
Maybe down the road I'd be interested in electronic ignition, but the very simple "Magnetron" system used by these engines is free and quite reliable (negatives: fixed advance). For now, EFI is the priority.
My very naive/uninformed thoughts:
1) Can we run the engine acceptably with just a throttle and a MAF input and run everything from that? No TPS, no temperatures, no RPM, etc. Bias a little bit to the rich side so the engine can increase RPM with increases in throttle, and the new (higher) MAF will drive the increase in injector "on" time? Would this method be self-compensating for altitude? A "mixture" knob in the cockpit for each cylinder could be used for fine-tuning (based on displayed EGT).
2) Similarly, could we get by with just RPM and absolute manifold pressure?
3) Just lambda? (aside from the reservations described above regarding leaded fuel). Sounds primitive, but if the engine is running, we can get the mixture right using lambda alone, and we bias the mixture to allow acceleration if the throttle is opened--would it work?
Or, can Free EMS accommodate some sort of graceful backup to any of the above (or other--better-- degraded operation modes) in the case of sensor failures? I don't think the sensor failures need to be detected automatically, our pilot can flip the switch to alternate modes if the engine starts running poorly.
Sorry for the too-lengthy first post. Thanks for any assistance.
I'm hoping to find/build an EFI system suitable for fitting to small (25-35 HP) V-twin industrial engines that are increasing popular in very small experimental aircraft. Most folks flying them are using carburetors, often the inexpensive ones from the OEMs. These can be fussy, and I think we can maybe do better.
The single most important attribute is reliability. Next is reliability. Ease of use and in setting it up will also be important. Fuel efficiency would be very welcome, but is less critical than remaining airborne. Low cost is desirable (the engines themselves cost approx $1000 new)
Megasquirt/Microsquirt could surely be made to work, but my impression is that the code is immense, not entirely transparent, and the cost isn't especially low. The problem (IMO) with huge software, which probably does a lot of great things across a wide variety of users, is that in this application it makes it hard to anticipate failure modes. I (think) I'd do best with the minimal number of sensors and rock-solid defaults that can be put in for any of them so the engine continues to chug along at sufficient output to remain safely airborne.
Attributes of this application:
-- Open loop is desirable, but closed loop might be acceptable if it proves best for other reasons. The most common fuel for general aviation in much of the world ("100LL") still contains tetraethyl lead. Lambda sensors don't like it. Still, users of these engines might be willing to take their own unleaded gasoline to the airport for local flying, if this proves to be the best way.
-- The uneven induction pattern of the V-twin engines requires separate induction and exhaust circuits for each cylinder. So, two injectors.
-- Contrary to automobile use, a smooth idle isn't very important, power settings are fairly constant and generally high. Air temperature and density will vary. Any "limp home" mode must prioritize adequate power output over preservation of the engine.
-- Users are generally willing to make adjustments in flight. They are used to carburetors requiring manual mixture adjustments, etc. CHT and EGT readouts for each cylinder will be available in the cockpit.
-- Power available: These engines generally have 16A alternators for the 12V electrical system, so about 200 watts produced. If we subtract other required power uses and a desire to avoid overtaxing the charging system, it would be best if we could limit the EFI to about 100 watts, if that is feasible.
-- Injection timing: not especially critical, especially if we can do away with an RPM input in the bargain (one less failure point). Squirt the fuel into the runner at the right rate and it'll get into the jug when air flows. Too cavalier?
-- The engines are air cooled, so there's no coolant temperature to monitor (though CHT is available).
Maybe down the road I'd be interested in electronic ignition, but the very simple "Magnetron" system used by these engines is free and quite reliable (negatives: fixed advance). For now, EFI is the priority.
My very naive/uninformed thoughts:
1) Can we run the engine acceptably with just a throttle and a MAF input and run everything from that? No TPS, no temperatures, no RPM, etc. Bias a little bit to the rich side so the engine can increase RPM with increases in throttle, and the new (higher) MAF will drive the increase in injector "on" time? Would this method be self-compensating for altitude? A "mixture" knob in the cockpit for each cylinder could be used for fine-tuning (based on displayed EGT).
2) Similarly, could we get by with just RPM and absolute manifold pressure?
3) Just lambda? (aside from the reservations described above regarding leaded fuel). Sounds primitive, but if the engine is running, we can get the mixture right using lambda alone, and we bias the mixture to allow acceleration if the throttle is opened--would it work?
Or, can Free EMS accommodate some sort of graceful backup to any of the above (or other--better-- degraded operation modes) in the case of sensor failures? I don't think the sensor failures need to be detected automatically, our pilot can flip the switch to alternate modes if the engine starts running poorly.
Sorry for the too-lengthy first post. Thanks for any assistance.