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  #11  
Old 01-15-2016, 08:51 PM
vluvelin vluvelin is offline
 
Join Date: Dec 2013
Location: Montreal
Posts: 205
Default BOSCH CIS injectors and RSA servo

Thank you Don.
Yes CIS metering unit is different but injectors have variable orifice design
it is changing with input pressure. more pressure compress spring and opens orifice.

it looks like same principle would work on RSA with higher pressure in injector line at idle. the only problem i see is operating pressures of RSA Servo and BOSCH injectors

injectors are starting to open at around 50psi depending on part number
and servo max input pressure is maxes at 50psi
as i understand atomization of fuel by injector is depending on high pressure
and it cant operate at lower pressure.

i am coming back to same question
Why RSA servo can not operate at higher pressure????? like 100 psi input
50-80 output?
I never take a part any RSA servo but from what i could find online it operates on deferential pressures and input pressure should not really make difference
Is there possibility to ajust size of main metering jet and diaphragm valve????
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  #12  
Old 01-16-2016, 08:11 AM
Don at Airflow Don at Airflow is offline
 
Join Date: Jun 2006
Posts: 316
Default Bosch CIS and RSA injection systems

You do not understand the principle of operation of the RSA injection system, thus my comment on the first reply. In reality we have operated RSA and our fuel injection systems up to 150 PSI inlet fuel pressure. This does not change the nozzle back pressure (which is dependent on orifice size and fuel flow). And again the CIS injector nozzles are nothing more than a pintle valve design with a cracking pressure of 50 PSI. The pressure drop probably stays fairly constant with flow depending on the spring rate and area of the pintle valve with fuel flow change. And yes the high pressure against the pintle valve is what atomizes the fuel. The fuel metering is done at the Fuel Distributer where an accurate pressure drop (4.5 bar) is held across the precisely sized metering slits that the valve plunger opens and closes. Since you are running a higher pressure drop across the metering slits (65 PSI) than the opening pressure of the pintle valve (50 PSI), it doesn?t matter if one pintle valve nozzle cracking pressure is slightly higher than another (within reason), all nozzles will get equal fuel at any fuel flow. You cannot do this with the current set up of a Bendix system. But there are other solutions to the problem that I will not divulge here.
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  #13  
Old 01-16-2016, 08:28 AM
Rupester Rupester is offline
 
Join Date: Dec 2005
Location: Mahomet, Illinois
Posts: 2,195
Default

Lest the earlier post slip by unnoticed, this is a shout-out for Don's Fuel Injection 101 class. For anyone running FI, or pondering running FI, the knowledge gained in Don's class is invaluable. You'll learn things that will benefit you and your airplane for years to come. ... Not to mention Don and his lovely bride will feed you well, and you'll likely get to meet and work with other RVers!
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