X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Received: from qw-out-2122.google.com ([74.125.92.26] verified) by logan.com (CommuniGate Pro SMTP 5.2.14) with ESMTP id 3691213 for flyrotary@lancaironline.net; Mon, 22 Jun 2009 13:37:38 -0400 Received-SPF: pass receiver=logan.com; client-ip=74.125.92.26; envelope-from=wdleonard@gmail.com Received: by qw-out-2122.google.com with SMTP id 8so1544609qwh.25 for ; Mon, 22 Jun 2009 10:37:05 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=gamma; h=domainkey-signature:mime-version:received:in-reply-to:references :date:message-id:subject:from:to:content-type; bh=gWr0bBcn7lCCPoNoMYe/fTtkLpXgisIM6mGzjxTGqNo=; b=Oghwihr8n+ozKByMURAQVM37nrRTDr+R9F34ckYN2XBhfpWSEmQyOoRlpaicLJkRXN l5PyP8wDHQ45H/NoBj/VOu5kgR6Nd/lMPm8rx4J7HN14kerq2a1lqcuJSwyH752+82O+ tJ9+oYW5sOEnhba9hJAq3AcbCcMQzZbqeIMfU= DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :content-type; b=mm23v74DzC0PymsVOCpgM4VbvhqH+BPELmHrcVK25GpOqIXL8PZ0sCtIU3wa9M+eGK uhJKQXQYLVHZQVh3gDEpUFSd33+UDAMdpEQ7hq13pMPL0QVcKbO3/SnaXDxVX2lHu2u4 XzecN0mxpgYX9H6vY6KRjEkU5RV1FFnrMnHQ0= MIME-Version: 1.0 Received: by 10.220.90.209 with SMTP id j17mr4268404vcm.61.1245692224913; Mon, 22 Jun 2009 10:37:04 -0700 (PDT) In-Reply-To: References: Date: Mon, 22 Jun 2009 10:37:04 -0700 Message-ID: <1c23473f0906221037g2eb29dcfl8022517ccaf9976@mail.gmail.com> Subject: Re: [FlyRotary] Re: Duty Cycle for Injectors From: David Leonard To: Rotary motors in aircraft Content-Type: multipart/alternative; boundary=0016e6475d8890c104046cf3521d --0016e6475d8890c104046cf3521d Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Cool, thanks for the low down on that one Gary! It always seemed strange to me the the injectors would have a durability issue with duty cycle. Lets see at 5700 RPM (what I use for a tach - hour) that is 342k cycles per hour. Then a billion cycles is about 3000 tach hours. Cool. (wonder how many cycles the car put on it before I bought them). Man, a billion sure is a big number. If you earned $342,000/hr - you would be very rich fast, but... Working 40 hrs/ week and never taking a vacation, it would still take 164 years to earn $1B. Dave Leonard On Mon, Jun 22, 2009 at 4:44 AM, Gary Casey wrote: > 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) > > -- David Leonard Turbo Rotary RV-6 N4VY http://N4VY.RotaryRoster.net http://RotaryRoster.net --0016e6475d8890c104046cf3521d Content-Type: text/html; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable
Cool, thanks for the low down on that one Gary!=A0 It always seemed st= range to me the the injectors would have a durability issue with duty cycle= .
=A0
Lets see at 5700 RPM (what I use for a tach - hour) that is 342k cycle= s per hour.=A0 Then a billion cycles is about 3000 tach=A0hours.=A0 Cool.= =A0 (wonder how many cycles the car put on it before I bought them).
=A0
Man, a billion sure is a big number.=A0 If you earned $342,000/hr - yo= u would be very rich fast, but...=A0 Working 40 hrs/ week and never taking = a vacation, it would still=A0take 164 years to earn $1B.=A0
=A0
Dave Leonard

On Mon, Jun 22, 2009 at 4:44 AM, Gary Casey <casey.gary@yahoo.= com> wrote:
Just a little historical anecdote:=A0 When we at Bendix were developin= g the very first US production=A0fuel injection system (remember the Coswor= th Vega?) we sized the injectors for about 80% on-time at maximum manifold = pressure, minimum air temperature and full power.=A0 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.=A0 But if the injector approaches = 100%, there will be a=A0pulse width less than 100%=A0when the injector will= stay fully open, creating a step in fuel flow.=A0 This=A0is a normal=A0occ= urence=A0during cold engine operation when the enrichment algorithm command= s 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 prett= y much ignored.=A0 The idea of sizing the injectors for 80% duty cycle had = nothing to do with racing applications, but it applies there, too.=A0 The o= bvious 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.=A0 Not a good thing.
=A0
Inceidentally, there is no concern for injector relaibility or durabil= ity.=A0 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 cy= cles that wears the injector.=A0 As injectors wear the flow generally incre= ases and most modern injectors are rated for a billion cycles with a flow i= ncrease of less than 3%.=A0 The coil is cooled by the fuel itself, so overh= eating is not a concern.
=A0
Gary Casey

-----Inline Message Follows-----=20


Ed,
I remember reading that the 80% duty c= ycle rule (of thumb)was originally developed for the racing industry.
=A0
Given that probably 100% will never be= reached in the day to day vehicle use -=A0the 80 % duty cycle=A0most proba= bly 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.
=A0
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 c= ruise is for the most part only 6,000 rpm, do we really have to held to the= 80% DC rule, where perhaps 90% DC=A0(for short periods of time) may well g= ive sufficient safety margin to maintain longevity of the injectors.=
=A0
Not that there is a major benefit in h= aving borderline injector duty cycle, as you so rightly pointed out - =A0it= 's just that it would be interes= ting to know!
George (down under)
=




--
David Leonard

Turbo Rotary RV-6 N4VY
http://N4VY.RotaryRoster.net
http://RotaryRoster.net
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