X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Received: from cdptpa-omtalb.mail.rr.com ([75.180.132.123] verified) by logan.com (CommuniGate Pro SMTP 5.2.14) with ESMTP id 3690785 for flyrotary@lancaironline.net; Mon, 22 Jun 2009 08:51:20 -0400 Received-SPF: pass receiver=logan.com; client-ip=75.180.132.123; envelope-from=eanderson@carolina.rr.com Received: from computername ([75.191.186.236]) by cdptpa-omta04.mail.rr.com with ESMTP id <20090622125042772.RTVI4077@cdptpa-omta04.mail.rr.com> for ; Mon, 22 Jun 2009 12:50:42 +0000 From: "Ed Anderson" To: "'Rotary motors in aircraft'" Subject: RE: [FlyRotary] Re: Duty Cycle for Injectors Date: Mon, 22 Jun 2009 08:50:47 -0400 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_000F_01C9F316.89976400" X-Mailer: Microsoft Office Outlook, Build 11.0.5510 In-Reply-To: Thread-Index: AcnzLuAQtVxok3s4TEGx+v4leAdr8wACJIWQ X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.5579 Message-Id: <20090622125042772.RTVI4077@cdptpa-omta04.mail.rr.com> This is a multi-part message in MIME format. ------=_NextPart_000_000F_01C9F316.89976400 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Thanks Gary for the background on the 80% on-time. Seems to be the standard, but never knew where it came from. Clearly 100% provides no further control of the air/fuel ratio which as you point out can be particularly bad for piston engines (or any boosted engine) but less so for the rotary. Given your statement that the full open position could occur at some point before 100% pulse duration would expect to keep it fully open - then some "margin" is clearly desirable - so it appears that 80% provides that margin. Ed Ed Anderson Rv-6A N494BW Rotary Powered Matthews, NC eanderson@carolina.rr.com http://www.andersonee.com http://www.dmack.net/mazda/index.html http://www.flyrotary.com/ http://members.cox.net/rogersda/rotary/configs.htm#N494BW http://www.rotaryaviation.com/Rotorhead%20Truth.htm _____ From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] On Behalf Of Gary Casey Sent: Monday, June 22, 2009 7:44 AM To: Rotary motors in aircraft Subject: [FlyRotary] Re: Duty Cycle for Injectors Just a little historical anecdote: When we at Bendix were developing the very first US production fuel injection system (remember the Cosworth Vega?) we sized the injectors for about 80% on-time at maximum manifold pressure, minimum air temperature and full power. This is a compromise, of course - a low-flow injector is desireable to have the most accuracy at idle when the pulse width is very short. But if the injector approaches 100%, there will be a pulse width less than 100% when the injector will stay fully open, creating a step in fuel flow. This is a normal occurence during cold engine operation when the enrichment algorithm commands more flow, but it turns out that a max engine speed there is little or no need for cold enrichment regardless of temperature, so the effect is pretty much ignored. The idea of sizing the injectors for 80% duty cycle had nothing to do with racing applications, but it applies there, too. The obvious problem encountered when undersizing the injectors is that once 100 duty cycle is reached the flow is limited - the engine will lean out if the rpm or air flow goes higher. Not a good thing. Inceidentally, there is no concern for injector relaibility or durability. It is a simple solenoid valve and running at 100% duty cycle would theoretically make it last longer - it is the total number of open-close cycles that wears the injector. As injectors wear the flow generally increases and most modern injectors are rated for a billion cycles with a flow increase of less than 3%. The coil is cooled by the fuel itself, so overheating is not a concern. Gary Casey _____ -----Inline Message Follows----- Ed, I remember reading that the 80% duty cycle rule (of thumb)was originally developed for the racing industry. Given that probably 100% will never be reached in the day to day vehicle use - the 80 % duty cycle most probably doesn't apply for sizing. However bigger injectors are standard in vehicles where the RPM limit is much higher than what we may experience in our Aviation application, even if for only short periods of time. Given that our RPM is on the high end for climb and take-off, but not as high as it could be (not max RPM), and cruise is for the most part only 6,000 rpm, do we really have to held to the 80% DC rule, where perhaps 90% DC (for short periods of time) may well give sufficient safety margin to maintain longevity of the injectors. Not that there is a major benefit in having borderline injector duty cycle, as you so rightly pointed out - it's just that it would be interesting to know! George (down under) __________ Information from ESET NOD32 Antivirus, version of virus signature database 3267 (20080714) __________ The message was checked by ESET NOD32 Antivirus. http://www.eset.com ------=_NextPart_000_000F_01C9F316.89976400 Content-Type: text/html; charset="us-ascii" Content-Transfer-Encoding: quoted-printable

Thanks Gary for the background on the 80% = on-time.

 

  Seems to be the standard, = but never knew where it came from.  Clearly 100% provides no further control of = the air/fuel ratio which as you point out can be particularly bad for piston engines = (or any boosted engine) but less so for the rotary.  Given your statement = that the full open position could occur at some point before 100% pulse duration would = expect to keep it fully open – then some “margin” is clearly desirable – so it appears that 80% provides that = margin.

 

 

 

Ed

 

From: = Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] On Behalf Of Gary Casey
Sent: Monday, June 22, = 2009 7:44 AM
To: Rotary motors in aircraft
Subject: [FlyRotary] Re: = Duty Cycle for Injectors

 

Just a little historical anecdote:  When we at Bendix were developing the very first US production fuel injection system (remember the Cosworth Vega?) we = sized the injectors for about 80% on-time at maximum manifold pressure, = minimum air temperature and full power.  This is a compromise, of course - a = low-flow injector is desireable to have the most accuracy at idle when the pulse = width is very short.  But if the injector approaches 100%, there will be a pulse width less than 100% when the injector will stay fully = open, creating a step in fuel flow.  This is a normal occurence during cold engine operation when the = enrichment algorithm commands more flow, but it turns out that a max engine speed = there is little or no need for cold enrichment regardless of temperature, so the = effect is pretty much ignored.  The idea of sizing the injectors for 80% = duty cycle had nothing to do with racing applications, but it applies there, too.  The obvious problem encountered when undersizing the = injectors is that once 100 duty cycle is reached the flow is limited - the engine = will lean out if the rpm or air flow goes higher.  Not a good = thing.

 

Inceidentally, there is no concern for injector relaibility or durability.  It is a simple solenoid valve and running at 100% duty = cycle would theoretically make it last longer - it is the total number of = open-close cycles that wears the injector.  As injectors wear the flow = generally increases and most modern injectors are rated for a billion cycles with = a flow increase of less than 3%.  The coil is cooled by the fuel itself, = so overheating is not a concern.

 

Gary Casey

 

-----Inline = Message Follows-----

Ed,

I remember reading that the 80% duty cycle rule (of thumb)was originally developed for the racing = industry.

 

Given that probably 100% will never be reached in the = day to day vehicle use - the 80 % duty cycle most probably doesn't = apply for sizing. However bigger injectors are standard in vehicles where the RPM = limit is much higher than what we may experience in our Aviation application, = even if for only short periods of time.

 

Given that our RPM is on the high end for climb and take-off, but not as high as it could be (not max RPM), and cruise is = for the most part only 6,000 rpm, do we really have to held to the 80% DC rule, = where perhaps 90% DC (for short periods of time) may well give sufficient = safety margin to maintain longevity of the = injectors.

 

Not that there is a major benefit in having = borderline injector duty cycle, as you so rightly pointed out -  it's just = that it would be interesting to know!

George (down under)




__________ Information from ESET NOD32 Antivirus, version of virus = signature database 3267 (20080714) __________

The message was checked by ESET NOD32 Antivirus.

http://www.eset.com

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