X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Received: from imr-mb02.mx.aol.com ([64.12.207.163] verified) by logan.com (CommuniGate Pro SMTP 5.3.8) with ESMTP id 4431484 for flyrotary@lancaironline.net; Sun, 15 Aug 2010 10:17:02 -0400 Received-SPF: pass receiver=logan.com; client-ip=64.12.207.163; envelope-from=Lehanover@aol.com Received: from imo-ma03.mx.aol.com (imo-ma03.mx.aol.com [64.12.78.138]) by imr-mb02.mx.aol.com (8.14.1/8.14.1) with ESMTP id o7FEGPr0027446 for ; Sun, 15 Aug 2010 10:16:25 -0400 Received: from Lehanover@aol.com by imo-ma03.mx.aol.com (mail_out_v42.9.) id q.cfd.7b04d95a (43957) for ; Sun, 15 Aug 2010 10:16:23 -0400 (EDT) Received: from magic-d26.mail.aol.com (magic-d26.mail.aol.com [172.19.146.160]) by cia-dd01.mx.aol.com (v129.4) with ESMTP id MAILCIADD016-abb54c67f6b737b; Sun, 15 Aug 2010 10:16:23 -0400 From: Lehanover@aol.com Message-ID: Date: Sun, 15 Aug 2010 10:16:23 EDT Subject: Re: [FlyRotary] Re: Turbo Questions To: flyrotary@lancaironline.net MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="part1_d996a.548c0dcb.399950b7_boundary" X-Mailer: AOL 9.5 sub 185 X-AOL-IP: 173.88.9.178 X-Spam-Flag:NO X-AOL-SENDER: Lehanover@aol.com --part1_d996a.548c0dcb.399950b7_boundary Content-Type: text/plain; charset="US-ASCII" Content-Transfer-Encoding: 7bit My driver could detonate a NA race engine at will. We had a 70 MPH first gear, so slipping the clutch was required to move the car up to speed for the pace lap. The proper procedure is to rev the engine to 3,000 RPM, release the throttle to zero and the clutch, so the car lunges using only the stored energy in the rotating assembly. Then repeat until the car is rolling along at a near zero throttle setting and the clutch is fully engaged. We had either a crank triggered ignition or an electronic distributor with no advance curve and about 25 degrees of advance. So with the clutch engaged the engine could not rev up to reduce cylinder filling, and 25 degrees of advance is way too much for 800 RPM. This is the same exact thing as too much ignition advance. Detonation is an ignition event remote from the spark plug(s) after the planned ignition event. Detonation is charge temperature dependant. Period. Think of turning a gasoline engine into a diesel engine. So for some reason the fuel air mixture (charge) has been overheated, and the pressure increase caused by the plug lighting part of the charge has raised the temperature of the remaining charge too high. Then part of the charge auto-ignites. Detonation. Heat of compression. Like a diesel engine, compressing a mass of air makes it hot. It matters not at all how it is compressed. It only matters how much. In the diesel perhaps an 18:1 ratio can raise the air temperature to above the flash point of the fuel to be injected. So no ignition system is required. The diesel injection period keeps the stresses low. In the gasoline engine detonating, the fuel is already in the chamber, so when the auto-ignition takes place the pressure rise is uncontrolled and may cause damage after only a few cycles, or in a boosted engine just one event. The greater the time difference in the split timing, the more pronounced the collision of the two flame fronts. In piston engines an attempt is made to keep the plugs firing together. Usually half of the plugs on top and half on the bottom of each cylinder are fired together. So a split timing would have assymetrical results. In the rotary there is little difference in performance of split over identical timing except at low RPM and for pollution control. The longer the split period, the more the second event looks like a detonation event. In high boost engines you want no split at all, and under high boost very little advance, maybe only 10 degrees of less. Charge temperatures are affected by chamber temps. So low oil temps (rotor cooling) and low water temps (the outer half of the combustion chamber) help resist detonation. Sudden throttle advances from low RPM (if no retard programming is available) can cause a problem. Cold heat range plugs and controlled engine temps eliminate nearly all problems. Lynn E. Hanover In a message dated 8/15/2010 9:03:56 A.M. Eastern Standard Time, eanderson@carolina.rr.com writes: Anytime you increase the internal compression pressure (either by increasing the compression ratio or through forced induction - which in effect increases the compression ratio) - the more efficiency and power you gain AND the closer you move to the detonation regime. The engine doesn't know or care how this increase in pressure comes about - well, actually it does. If you use a turbo or supercharger you are also heating the air through their compression process (which is why you need an intercooler in many cases) thereby moving closer to detonation. Lower compression engine are further away from the detonation regime to start with and therefore can safely take a higher boost level (and benefits more from it) than a high compression engine. So as has been mentioned, you will see a higher performance enhancement by boosting a low compression engine than an high compression engine already running closer to the detonation regime. You can certainly boost high compression engine, but to do it safely you generally need some fairly sophisticated "Knock" sensing and ignition/boost control to keep it out of detonation. Naturally the more boost you run the less margin for any error in controlling the onset of detonation. Contrary to what you may have read, it is possible to get an N/A rotary engine to detonate - I managed to do that in early flight (1998) by inadvertently over-advancing my ignition timing. I mistakenly set the static timing to 45Deg BTDC. I took off and after getting airborne noticed that if I opened the throttle wide open (more combustion pressure), the exhaust sound changed to a staccato, popping sound. Retard the throttle and it went away, never liking it when the engine did anything abnormal I returned and landed. Upon pulling the spark plugs I found I had destroyed them (presumably through detonation). The leading plugs had the ceramic cones completely missing and the electrodes were almost completely eroded away so that the spark gap was over 3/16", The trailing plugs had not suffer quite as badly although the ceramic cone was cracked on both and their electrodes also eroded. So my personal opinion is that unless there is some flight regime that requires it (you fly out of mountain valleys, you normally cruise above 12000 MSL, etc), you need to assess whether the extra weight, complexity and cost are worth it. If it is then go for it. In my case, after thinking about how I normally fly, I came to the conclusion that for me a turbo would not be worthwhile - which is why I still have two sitting on my work bench - well, the other reason is that they are stock Mazda turbos and really not suited for aircraft use (unless perhaps used very modestly) as I think John Slade has demonstrated for us all. Turbocharging an aircraft is a very interesting challenge and I sometimes wish I had talked myself into it - but, the numbers just didn't work for me and my typical flying. Fortunately for those of you who are going to turbocharge the rotary, you have some pioneers who are providing you with knowledge that was gained at some expense (money, underwear, seat cusions, etc) {:>). So make use of it and good luck. Ed --part1_d996a.548c0dcb.399950b7_boundary Content-Type: text/html; charset="US-ASCII" Content-Transfer-Encoding: quoted-printable
My driver could detonate a NA race engine at will. We had a 70 MP= H=20 first gear, so slipping the clutch was required to move the car up to spee= d for=20 the pace lap. The proper procedure is to rev the engine to 3,000 RPM, rele= ase=20 the throttle to zero and the clutch, so the car lunges using only the stor= ed=20 energy in the rotating assembly. Then repeat until the car is rolling alon= g at a=20 near zero throttle setting and the clutch is fully engaged. We had either= a=20 crank triggered ignition or an electronic distributor with no advance curv= e and=20 about 25 degrees of advance. So with the clutch engaged the engine could= not rev=20 up to reduce cylinder filling, and 25 degrees of advance is way too much= for 800=20 RPM. This is the same exact thing as too much ignition advance.
 
Detonation is an ignition event remote from the spark plug(s) aft= er the=20 planned ignition event. Detonation is charge temperature=20 dependant. Period. Think of turning a gasoline engine into a dies= el=20 engine. So for some reason the fuel air mixture (charge) has been overheat= ed,=20 and the pressure increase caused by the plug lighting part of the charge= has=20 raised the temperature of the remaining charge too high. Then part of the= charge=20 auto-ignites. Detonation.
 
Heat of compression. Like a diesel engine, compressing a mass of= air=20 makes it hot. It matters not at all how it is compressed. It only matters= how=20 much. In the diesel perhaps an 18:1 ratio can raise the air temperature to= above=20 the flash point of the fuel to be injected. So no ignition system is requi= red.=20 The diesel injection period keeps the stresses low. 
 
In the gasoline engine detonating, the fuel is already in the cha= mber,=20 so when the auto-ignition takes place 
the pressure rise is uncontrolled and may cause damage after only= a few=20 cycles, or in a boosted engine just one event.
 
The greater the time difference in the split timing, the more=20 pronounced the collision of the two flame fronts. In piston engines an att= empt=20 is made to keep the plugs firing together. Usually half of the plugs on to= p and=20 half on the bottom of each cylinder are fired together. So a split timing= would=20 have assymetrical results.
 
In the rotary there is little difference in performance of split= over=20 identical timing except at low RPM and for pollution control. The longer= the=20 split period, the more the second event looks like a detonation event.=20
 
In high boost engines you want no split at all, and under high bo= ost=20 very little advance, maybe only 10 degrees of less.
 
Charge temperatures are affected by chamber temps. So low oil tem= ps=20 (rotor cooling) and low water temps
(the outer half of the combustion chamber) help resist detonation= .=20
 
Sudden throttle advances from low RPM (if no retard programming= is=20 available) can cause a problem.
 
Cold heat range plugs and controlled engine temps eliminate nearl= y all=20 problems.
 
Lynn E. Hanover
 
 
 
 
 
 
In a message dated 8/15/2010 9:03:56 A.M. Eastern Standard Time,=20 eanderson@carolina.rr.com writes:
Anytime=20 you increase the internal compression pressure (either by increasing the=20 compression ratio or through forced induction - which in effect
incr= eases=20 the compression ratio)  - the more efficiency and power you gain AND=20 the closer you move to the  detonation regime.  The engine doe= sn't=20 know
or care how this increase in pressure comes about - well, actua= lly it=20 does.
If you use a turbo or supercharger you are also heating the ai= r=20 through
their compression process (which is why you need an intercoo= ler in=20 many
cases) thereby moving closer to detonation.

Lower compre= ssion=20 engine are further away from the detonation regime to
start with and= =20 therefore can safely take a higher boost level (and benefits
more fr= om it)=20 than a high compression engine.  So as has been mentioned, you
= will=20 see a higher performance enhancement by boosting a low compression
e= ngine=20 than an high compression engine already running closer to the
detona= tion=20 regime.

You can certainly boost high compression engine, but to= do it=20 safely you
generally need some fairly sophisticated "Knock" sensing= and=20 ignition/boost
control to keep it out of detonation.  Naturally= the=20 more boost you run the
less margin for any error in controlling the= onset=20 of detonation.

Contrary to what you may have read, it is possible= to=20 get an N/A rotary
engine to detonate - I managed to do that in early= =20 flight (1998) by
inadvertently over-advancing my ignition timing.&nb= sp; I=20 mistakenly set the
static timing to 45Deg BTDC.  I took off and= after=20 getting airborne noticed
that if I opened the throttle wide open (mo= re=20 combustion pressure), the
exhaust sound changed to a staccato, poppi= ng=20 sound.  Retard the throttle and
it went away, never liking it= when=20 the engine did anything abnormal I
returned and landed.

Upon= =20 pulling the spark plugs I found I had destroyed them (presumably
thr= ough=20 detonation).  The leading plugs had the ceramic cones completely=20
missing and the electrodes were almost completely eroded away so tha= t the=20
spark gap was over 3/16",  The trailing plugs had not suffer qu= ite as=20 badly
although the ceramic cone was cracked on both and their electr= odes=20 also
eroded.

So my personal opinion is that unless there is= some=20 flight regime that
requires it (you fly out of mountain valleys, you= =20 normally cruise above
12000 MSL, etc), you need to assess whether th= e=20 extra weight, complexity and
cost are worth it.  If it is then= go for=20 it.

In my case, after thinking about how I normally fly, I came= to the=20
conclusion that for me a turbo would not be worthwhile - which is wh= y I=20
still have two sitting on my work bench - well, the other reason is= that=20
they are stock Mazda turbos and really not suited for aircraft use= (unless=20
perhaps used very modestly) as I think John Slade has demonstrated= for us=20
all.  Turbocharging an aircraft is a very interesting challenge= and I=20
sometimes wish I had talked myself into it - but, the numbers just= didn't=20
work for me and my typical flying.

Fortunately for those of= you who=20 are going to turbocharge the rotary, you
have some pioneers who are= =20 providing you with knowledge that was gained at
some expense (money,= =20 underwear, seat cusions, etc) {:>).  So make use of it
and= good=20 luck.

Ed

--part1_d996a.548c0dcb.399950b7_boundary--