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Northwest727
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Posts: 379
Joined: Sat Jul 30, 2005 10:38 am

Exactly How Does RSA Fuel Injection Work?

Wed Mar 16, 2011 7:03 pm

Looking at Google, and even asking some A&Ps, I'm still confused.

I understand how the servo regulator works, so no explanation needed, but I have a few questions about what happens afterwords, more specifically, the flow distributor (spider valve, manifold valve) and the actual injectors.

1. First off, many sources say that the RSA system used in both Lycomings and Continentals is of the continuous-flow type. Does this mean that fuel is always spraying from the injectors, even if the injectors' associated cylinder is not in the intake cycle? i.e., instead of injecting the right amount of fuel into the cylinder the moment the intake valve opens, its always spraying, even when the valve is closed?

2. Two, do the injectors even deliver a "measured" amount of spray to the respective cylinder? Since there is no electronic computer doing calculations, is seems to me that the RSA system while simple, must be kind of "dumb."

3. Three, what is the purpose of the flow distributor? I understand its some kind of valve, but why? If it was measuring the amount of fuel to each of the cylinders, why not have the injectors do it, like on a car?

4. And finally, the prime procedure (at least on a Lycoming) calls to turn the auxiliary pump on, mixture full rich until a rise in fuel flow, and then mixture idle cut-off. Are we priming all the cylinders (like you would on a carbureted engine), or only those that are in the intake cycle (see question 1).

Thanks in advanced, and sorry for the bombardment of questions.
 
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jetmech
Posts: 2382
Joined: Wed Mar 29, 2006 2:14 am

RE: Exactly How Does RSA Fuel Injection Work?

Wed Mar 16, 2011 9:48 pm

Quoting Northwest727 (Thread starter):
1. First off, many sources say that the RSA system used in both Lycomings and Continentals is of the continuous-flow type. Does this mean that fuel is always spraying from the injectors, even if the injectors' associated cylinder is not in the intake cycle? i.e., instead of injecting the right amount of fuel into the cylinder the moment the intake valve opens, its always spraying, even when the valve is closed?

From what I can tell, yes. The RSA system sprays fuel onto the back of the intake valve at all times. The resulting fuel-air mixture is pulled into the cylinder when the intake valve opens.

Quoting Northwest727 (Thread starter):
2. Two, do the injectors even deliver a "measured" amount of spray to the respective cylinder? Since there is no electronic computer doing calculations, is seems to me that the RSA system while simple, must be kind of "dumb."

The required fuel for the entire engine (all cylinders) is metered via the venturi measuring device. This metered amount of fuel changes according to the flow rate of air through the venturi. As far as I can tell, the injectors themselves play no part in adjusting the amount of fuel delivered to the cylinders.

Quoting Northwest727 (Thread starter):

3. Three, what is the purpose of the flow distributor? I understand its some kind of valve, but why? If it was measuring the amount of fuel to each of the cylinders, why not have the injectors do it, like on a car?

The metering of fuel is a task that is centralised and carried out by the metering venturi. The total amount of fuel metered for all cylinders is divided evenly by the flow distributor, these smaller amounts of fuel being delivered to each injector.

Quoting Northwest727 (Thread starter):
but I have a few questions about what happens afterwords, more specifically, the flow distributor (spider valve, manifold valve) and the actual injectors.

Systems such as the RSA are not really considered to be "true" fuel injection systems. They are really more akin to an advanced carburetor. I suspect that the RSA system give you some of the benefits of a true fuel injection system without the complexity of developing all the associated software and hardware required by a true EFI system.

http://www.sacskyranch.com/rsaschematic.jpg
http://www.sacskyranch.com/rsaschematic.jpg

http://www.precisionairmotive.com/Publications/15-812_b.pdf
http://www.kellyaerospace.com/articles/ContinuousFlow.pdf

Regards, JetMech
JetMech split the back of his pants. He can feel the wind in his hair :shock: .
 
KELPkid
Posts: 5247
Joined: Wed Nov 02, 2005 5:33 am

RE: Exactly How Does RSA Fuel Injection Work?

Wed Mar 16, 2011 11:12 pm

Quoting jetmech (Reply 1):
Quoting Northwest727 (Thread starter):
1. First off, many sources say that the RSA system used in both Lycomings and Continentals is of the continuous-flow type. Does this mean that fuel is always spraying from the injectors, even if the injectors' associated cylinder is not in the intake cycle? i.e., instead of injecting the right amount of fuel into the cylinder the moment the intake valve opens, its always spraying, even when the valve is closed?

From what I can tell, yes. The RSA system sprays fuel onto the back of the intake valve at all times. The resulting fuel-air mixture is pulled into the cylinder when the intake valve opens.

Automotive fuel injection systems (especially the cheaper ones employed by US manufacturers through the mid-1980's) were like this. It would eventually lead to nasty intake valve carbon buildups. I didn't believe my mechanic on this until he pulled the cylinder heads off of the 3.8 litre V6 in my 1984 Thunderbird because I had a sticking intake valve. The car had about 130,000 miles at that point...Ford's CFI fuel injection system on that engine was a continuous spray type of system
Celebrating the birth of KELPkidJR on August 5, 2009 :-)
 
411A
Posts: 1788
Joined: Mon Nov 12, 2001 10:34 am

RE: Exactly How Does RSA Fuel Injection Work?

Thu Mar 17, 2011 2:41 am

Quoting jetmech (Reply 1):
They are really more akin to an advanced carburetor.

A pressure carbuertor, except that the fuel is delivered to each cylinder, instead of the carburetor body.
 
TSS
Posts: 3738
Joined: Fri Dec 29, 2006 3:52 pm

RE: Exactly How Does RSA Fuel Injection Work?

Sat Mar 19, 2011 8:14 am

Quoting 411A (Reply 3):
Quoting jetmech (Reply 1):
They are really more akin to an advanced carburetor.

A pressure carbuertor, except that the fuel is delivered to each cylinder, instead of the carburetor body.

Very much like the old Bosch K-Jetronic fuel injection system that was so common on European cars in the late 70s/early 80s-
http://en.wikipedia.org/wiki/Jetronic
Able to kill active threads stone dead with a single post!
 
Northwest727
Topic Author
Posts: 379
Joined: Sat Jul 30, 2005 10:38 am

RE: Exactly How Does RSA Fuel Injection Work?

Mon Mar 21, 2011 4:23 pm

As always jetmech, thanks for the detailed reply.

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