Help Support Homebuilt Aircraft & Kit Plane Forum:
Why do you think Avgas is ending? GAMI and Swift are both producing UL avgas now to replace 100LL with STCs for hundreds of engine types.
Last edited:
In EU we have closed our latest plant which produces that lead additive to fuel.
PMD
Well-Known Member
In defense of CI vs SI: EVERY diesel now certified has a dismal power/weight ratio. Once someone comes up with Rotax power density (that is IMHO the benchmark) things will change.
Numbers on 912 ul/uls / 914 /dv6
Uls/Ul - 88kg firewallforward,
914 - 104kg
Dv6 - 107kg.
SI/CI shows 25% of better bsf. For Cl. So we want to save 19kg of fuel per you mission to be on pair with SI.
And it looks like if our mission needs 76kg of fuel - CI will be on par with it.
And, yes it will hurt us on shorter trips..
Uls/Ul - 88kg firewallforward,
914 - 104kg
Dv6 - 107kg.
SI/CI shows 25% of better bsf. For Cl. So we want to save 19kg of fuel per you mission to be on pair with SI.
And it looks like if our mission needs 76kg of fuel - CI will be on par with it.
And, yes it will hurt us on shorter trips..
Rotax 912 iS Efficiency: Better than Claimed - Aviation Consumer
When Rotax surprised us last year with the rollout of its new 912 iS engine, we were skeptical of a claimed 20 percent improvement in fuel economy against the old standby 912 ULS. In a four-cylinder, high-RPM geared engine, that sounded like an overpromise.
www.aviationconsumer.com
That's some very good performance from the fuel injected Rotax. From the article:
+++++++++++++
"The 912 iS ECU is programmed to run in eco mode at 77 percent power or less, at which point the engine will operate at what European engineers know as Lambda 1, or a stoichiometric air-to-fuel ratio of 14 to 1. Without providing much detail, Rotax said the 912 iS is also capable Lambda 1.3 or lean-of-peak operation. In power mode, it runs at about Lambda 0.8 or 0.9."
++++++++++++++++
From the operator manual, the ECU depends on the following sensors:
"Throttle valve position, engine speed, intake air temp, ambient pressure, manifold pressure, exhaust temperature."
So, in keeping with their discussion of lean-of-peak operations and Lambda, how does the system determine the AFR without using an O2 sensor? Is it operating in a closed loop mode, but using EGT as the feedback sensor (just as a pilot might adjust mixture manually by reference to EGT)?
The Rotax redundant ECU setup seems very sophisticated (aka a thicket of complexity to troubleshoot). The CANBUS system can help, I guess, or it can introduce another batch of complexity.
+++++++++++++
"The 912 iS ECU is programmed to run in eco mode at 77 percent power or less, at which point the engine will operate at what European engineers know as Lambda 1, or a stoichiometric air-to-fuel ratio of 14 to 1. Without providing much detail, Rotax said the 912 iS is also capable Lambda 1.3 or lean-of-peak operation. In power mode, it runs at about Lambda 0.8 or 0.9."
++++++++++++++++
From the operator manual, the ECU depends on the following sensors:
"Throttle valve position, engine speed, intake air temp, ambient pressure, manifold pressure, exhaust temperature."
So, in keeping with their discussion of lean-of-peak operations and Lambda, how does the system determine the AFR without using an O2 sensor? Is it operating in a closed loop mode, but using EGT as the feedback sensor (just as a pilot might adjust mixture manually by reference to EGT)?
The Rotax redundant ECU setup seems very sophisticated (aka a thicket of complexity to troubleshoot). The CANBUS system can help, I guess, or it can introduce another batch of complexity.
Last edited:
Open loop. Alpha-N alhorithm. Less precise than lambda one, but more robust.
They would have to know at least MAP or MAF and/or possibly baro to do this. Throttle angle doesn't tell you much on an airplane engine since it operates at vastly different altitudes.
I would not use Alpha-N, and I would be surprised if many do.
Almost all efficient motors use a speed/density or a MAF system with 02 feedback. In the case of using Leaded fuel- which I have no idea why anyone would want to do that in a modern engine- the wideband 02 would be used for initial and perhaps periodic calibration- say every hundred hours or so- and then removed from the system and plugged.
Now in aircooled engines, I think the challenge in an EFI, turbocharged, flight engine would be the predictable high CHT at full throttle and boost. Aerovee limits full power use to I think 3 minutes? There are a couple of things that can be done to help. Right out of the gate a water/alcohol injection system would allow for higher boost levels with greatly reduced detonation risk with the side benefit of cleaning the combustion chambers. Yeah, I know, its one more thing to check, like fuel and oil, but with modern ECUs the boost level simply cannot be reached if there is no water to inject. Aerovee is not intercooling the compressed charge, and I think that is a huge mistake on an aircooled engine. Regardless of what the intake air temp is the act of compressing it heats that air up and that is all bad when you are trying to limit risk of detonation. A very simple air/air intercooler would go a long way. Lastly, in an aircooled engine, E85 fuel instead of 100LL will likely offer a lot of benefits over 100LL. With the E85 the engine can be run very lean without overheating the cyl heads. The risk of detonation is almost non-existent in high boost modes, and of course, it keeps the engine very clean and removes carbon buildup which in itself helps lower the risk of detonation. Yes, I am very well aware of the propensity to need to burn more of it- roughly 1/3 more in some situations- however with careful tuning in high compression engines the fuel usage was very comparable to "pump gas".
I like the idea of small and powerfull diesel engines, and the Mazda skyactiv diesel is really cool.
Maybe Rotax is getting these BSFC numbers using relatively good open loop logic (MAP, baro, RPM and temp) and they've just built their fuel tables to appropriately lean the injection when the engine isn't being asked to make much power (e.g low MAP relative to RPM). I dunno. But they aren't warning against leaded fuel (except as it affects valves), and they apparently aren't using an O2 sensor in normal ops.
Exactly. Sad that it is not available in 1.4-1.6 liter size. Coolnes due to its lower compression ratio...
On maf or map - agree. But is still a game of how much we need sensor to run it in high efficiency, and how much for limp home mode.
That is exactly how it works.
In the engines that ran on leaded fuel (few and far between these days) if the wideband dies it simply defaults to open loop and runs off of "hopefully" well done calibrations. In general the engine will not run as lean as it might in closed loop, but with good base calibration and trim tables it should be close.
In most modern EFI, the only sensors 100% necessary for the engine to run are the crank and cam sensors. The other sensors have default values that, if they fail the ECU uses that value and trim tables in thier place.
Of all the things I think about when considering EFI system failure sensor issues are pretty far down the list.
But we all want drip carburator as our fadec unit. With magnetos..
Not me. Not even a little bit.
In a plane that can accommodate gravity feed from the fuel tank, I'd think a floatless carburetor (e.g. Lake, POSA, RevFlow, AeroInjector, etc) could make an easy, light, reliable backup to an EFI system. It's little more than a calibrated fuel leak (tapered needle that admits more fuel as the slide throttle is opened) that varies mostly by throttle position, a little bit due to airflow rate past the needle. Since the EFI needs a throttle body anyway, these carbs can serve that purpose. No venturi (so little chance of icing), no fuel pump (so no electricity needed). If the EFI crumps out, just open the mixture knob to the carb and let that fuel start flowing.
With a well designed and installed EFI, it would probably never be needed.
Last edited:
Dual ECUs with dual sensor suites as Rotax does on their iS engines and we do on Lyconentals. No limp mode in aircraft ECUs since you need relatively high power to maintain flight compared to automotive applications where you only need 20-30 hp to limp home. Most sensors outside of crank sensors are not needed to keep the engine running to get you home safely if you mitigate with defaults.
Latest posts
-
-
-
-
Low cost vibration sensing for analysis
- Latest: crusty old aviator
-
-
-
