Got e from Zoche, near production

[rv6ejguy]

Originally Posted by Garth

But like I say, Kirk Creelman says he has checked them out extensively and they are solid....HE says. But time for telling is very near. They have several flying now and more every week.

We supplied Kirk with some EFI systems for Jabirus many years ago now if my memory serves me. These were a disaster at the time with multiple short term valve and head failures. He ditched these pretty quickly. I hope the Crossflow engines do the job for him and he gets good service from them. The Subaru EG33 base is a wonderful piece of engineering IMO if you don't screw with the thing very much.

[David-aviator]

Originally Posted by rv6ejguy

...... The Subaru EG33 base is a wonderful piece of engineering IMO if you don't screw with the thing very much.

I have been wondering since day one about the efforts of Jan Eggenfellner and Robert Paisley to reduce fuel consumption with the 3.0 H6 by reducing fuel pressure. I am running at about 32 psi as per the recommendation but no one has ever answered the question, why was the engine designed to run at 43.5 psi by Subaru and why is the mixture so rich at high power settings at this pressure?

A/F flow ratios have been confirmed at the lower pressure but is the assumption, that 12:1 to 15:1 is normal for a gasoline engine, valid with this engine? Only time will tell.

The ECU your company has developed obviously controls fuel flow differently than by reducing pressure. My engine has three O2 sensors, at least one of which does measure A/F ratio but this information is only used at low power, like going down the highway at 55 mph. Why does the ECU insist on running the engine so rich at high power? It reverts to computer tables (open loop) for fuel flow ignoring the sensors at relatively low power going up. Could it mean the engine needs a ratio of 11 or 10:1 to develop rated power or to protect it from excessive combustion heat? The compression ratio of this beast is 10.7:1 and perhaps the internal dynamics are quite different than running at say, 8:1, with older technology.

[rv6ejguy]

Originally Posted by David-aviator

I have been wondering since day one about the efforts of Jan Eggenfellner and Robert Paisley to reduce fuel consumption with the 3.0 H6 by reducing fuel pressure. I am running at about 32 psi as per the recommendation but no one has ever answered the question, why was the engine designed to run at 43.5 psi by Subaru and why is the mixture so rich at high power settings at this pressure?

A/F flow ratios have been confirmed at the lower pressure but is the assumption, that 12:1 to 15:1 is normal for a gasoline engine, valid with this engine? Only time will tell.

The ECU your company has developed obviously controls fuel flow differently than by reducing pressure. My engine has three O2 sensors, at least one of which does measure A/F ratio but this information is only used at low power, like going down the highway at 55 mph. Why does the ECU insist on running the engine so rich at high power? It reverts to computer tables (open loop) for fuel flow ignoring the sensors at relatively low power going up. Could it mean the engine needs a ratio of 11 or 10:1 to develop rated power or to protect it from excessive combustion heat? The compression ratio of this beast is 10.7:1 and perhaps the internal dynamics are quite different than running at say, 8:1, with older technology.

The issue with the OE ECU is that to protect the engine at high power settings and make max power, the ECU does not operate in closed loop (around 14.7 AFR) under these conditions, generally defaulting to open loop tables and an AFR of around 12.8 to 13.1 to 1. Because aircraft applications generally operate above this rpm and load point, they are almost always in open loop.

In order to reduce fuel flow then, the easiest way is to reduce fuel pressure. Closed loop is not affected by this change as the ECU re-trims injector pulse width to compensate. The question is, what is a safe AFR to run at high power settings? That can really only be answered by getting a lot of flight time on engines running leaner than what the factory did and seeing how long they last.

With a programmable ECU many more possibilities are open for AFR vs. HP including targeted AFRs vs. HP using a wideband O2 sensor.

In my view, there is rarely if ever a need to be richer than 13 to 1 AFR.

I lean my turbo EJ22 out to around 13.8 to 1 in cruise and use about 13 to 1 for takeoff and climb. This results in an EGT of around 1400F.

[mgomez]

Originally Posted by David-aviator

why was the engine designed to run at 43.5 psi by Subaru and why is the mixture so rich at high power settings at this pressure?

Probably because in a car, high-power operation is usually brief. Nobody cares what mileage a car gets during highway overtaking or climbing a hill because those operations don't last long enough to notice at the pump.

Therefore, it's safest to operate very rich during those brief periods to avoid knocking. It probably also makes the engine control system more tolerant of faulty sensors.

Airplanes engines, of course, spend most of their lives operating at those high power settings, so we care very much how close to stoichiometric mixture they operate. Conversely, the fuel economy at 20-30 HP (typical highway load in a Subaru car) is much less important in an airplane...that's descent power.