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Old 03-24-2012, 09:51 PM   #66
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Location: Long Beach, CA
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Originally Posted by roger 04 rt View Post

The Wideband O2 project has taken the richer mixtures route so far. Although I'm considering getting a matched set of injectors and seeing how much the AFR can be pushed in the lean direction.
Injector balance does make a difference on aircraft motors. Far more so than on a road vehicle. As a pilot you certainly know much about what's explained below. But the injector issue that causes a surging problem on the 1100/1150 isn't really related to the injectors. It relates to batch injection verses sequential injection.

For a 'continuous flow' aircraft fuel injection system injector balance is very relevant. Injector flow rate makes a big difference in an aircraft continuous flow system because the injector is merely an orifice. Fuel is flowing 100% of the time, and at the same rate, for the full 720 of the combustion cycle. In an aircraft continuous injection system, all injectors are on, all the time. An electronic fuel injector is on only a small portion of the time.

In addition, the motor in an aircraft at cruise is operating at a very high 'percentage of full power' setting. Certainly a very high power setting compared to that of a road vehicle at highway speeds, which is closer to 15%.

Any injector imbalance on an aircraft motor is amplified by the the continuous flow rate, and the high power settings. Any imbalance error is multiplied 10 fold at least. It's a cumulative error, you know?

Injector imbalance on a road vehicle at highway speeds or lower doesn't make too much of a difference. The low power settings and intermittent injection period limits the accumulated error. Injector imbalance makes a little difference in smoothness, but it isn't a source of surging.

The oilhead boxer motor has 'batch injection'. Batch injection, especially on a two-cylinder motor, makes a significant contribution to surging.

It's a little hard to explain. To summarize it's caused by the fuel charge arriving in two pieces, not one. That's what 'batch injection' is, multiple cylinders are injected as a batch. The result is the fuel for one cylinder arrives in the intake port at a different part of the 4-stroke combustion cycle than for the other cylinder. Which means that at the moment the respective intake valve opens, the fuel for that cylinder will be at a different degree of vaporization than the other. Unvaporized fuel does not combust. The difference in available combustible fuel radically changes the power level for that cycle.

A pretty good explanation of the fuel vaporization topic is in this Wall-Adhered Fuel patent.

How did this happen? Because the Motronic ECU on the 1100/1150 is a single cylinder device. Bosch called it Monotronic. Here's how the 'mono cylinder ECU' works on a two cylinder motor. As far as the ECU is concerned it is operating a single-cylinder motor, but one that's one-fourth the total displacement of the two cylinders, and turning at twice the RPM.

But all of the above aside, and as you've experienced, if the fuel mixture is increased a little it cures a lot of ills.


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Poolside screwed with this post 03-24-2012 at 09:57 PM
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