---------------------------------------------------------- JabiruEngine-List Digest Archive --- Total Messages Posted Sat 10/23/10: 4 ---------------------------------------------------------- Today's Message Index: ---------------------- 1. 03:00 AM - Re: Temps (Lynn Matteson) 2. 06:09 AM - Re: Temps (BobsV35B@aol.com) 3. 02:40 PM - Re: Temps (Mark Hubelbank) 4. 04:47 PM - Re: Temps (BobsV35B@aol.com) ________________________________ Message 1 _____________________________________ Time: 03:00:57 AM PST US From: Lynn Matteson Subject: Re: JabiruEngine-List: Temps Bob- Just to clarify, when you said: " If you want to use more than seventy-five per cent power, you need to run at least 150, preferably 250 degrees F above peak EGT. At those higher power settings, we need the extra fuel to slow the burning rate so that we can avoid detonation," I'm sure you meant to say **150, preferable 250 degrees richer (or cooler) than peak EGT** didn't you? Mark, Bob, and others- Where are you getting the figures for the percentages of power? Everybody talks about these percentages, but I don't see the flows, the manifold pressure numbers, or whatever the criteria is for establishing these percentages written as it pertains to the Jabiru line of engines. Lynn Matteson Kitfox IV Speedster, taildragger Jabiru 2200, #2062 Sensenich 62"x46" Wood (summer) Electroair direct-fire ignition system Rotec TBI-40 injection Status: flying...1054 hrs (since 3-27-2006) ________________________________ Message 2 _____________________________________ Time: 06:09:05 AM PST US From: BobsV35B@aol.com Subject: Re: JabiruEngine-List: Temps Good Morning Lynn, Yes! Glad you caught that. I was thinking about needing more fuel, but I sure did not get it written that way! The reason we want to be that rich is so that the rate of burn (Actually it is a bit more complicated because the burn is just as fast but the fuel takes longer to get burning that fast).is slower. That moves the point of peak cylinder pressure further along on the stroke and reduces the peak cylinder pressure. The actual temperature of the EGT is immaterial. It is just that EGT is a good, low cost, and convenient, indicator of what is happening to the combustion process. They key is to control that peak cylinder pressure. The history of using EGT as an indicator is all about how Al Hundere brought us to using his ALCOR unit (Al's Corporation.) He was trying to figure out some way to add a torque meter to our small engines when he noted the variances of the EGT on his dynamometer. He noted that while the EGT gauges of the day were not extremely accurate, they did indicate the peak quite accurately. By advising us to run richer or leaner than peak EGT he gave us the same information as was used in those big round engines that were equipped with torquemeters. That is why ALCOR never used precise temperatures. The actual EGT temperature means nothing. It is it's relation to peak EGT that tells us where the compression process is going. What we really want to know is where the mixture is in relation to best power mixture! Does that help a bit or have I muddied the water again? As to where the numbers come from for the Jabiru, in my case it is a WAG based on the principle that all internal combustion engines run the same and are affected the same way, but our aircraft engines are all designed to run rich to cool properly at full power and to cool properly at cruise power using best power mixtures. That is why Continental says to run rich above sixty-five per cent power and Lycoming uses seventy-five percent. If you try to nail either's engineers down to something more precise, they will tell you it all depends and my WAG is that the JABIRU engineers went through the same process as did the others. Happy Skies, Old Bob In a message dated 10/23/2010 5:01:08 A.M. Central Daylight Time, lynnmatt@jps.net writes: --> JabiruEngine-List message posted by: Lynn Matteson Bob- Just to clarify, when you said: " If you want to use more than seventy-five per cent power, you need to run at least 150, preferably 250 degrees F above peak EGT. At those higher power settings, we need the extra fuel to slow the burning rate so that we can avoid detonation," I'm sure you meant to say **150, preferable 250 degrees richer (or cooler) than peak EGT** didn't you? Mark, Bob, and others- Where are you getting the figures for the percentages of power? Everybody talks about these percentages, but I don't see the flows, the manifold pressure numbers, or whatever the criteria is for establishing these percentages written as it pertains to the Jabiru line of engines. Lynn Matteson Kitfox IV Speedster, taildragger Jabiru 2200, #2062 Sensenich 62"x46" Wood (summer) Electroair direct-fire ignition system Rotec TBI-40 injection Status: flying...1054 hrs (since 3-27-2006) ________________________________ Message 3 _____________________________________ Time: 02:40:36 PM PST US From: Mark Hubelbank Subject: Re: JabiruEngine-List: Temps Lynn, I don't have a manifold pressure indicator yet so I am going by fuel burn. At best a spark ignition engine generates 15 HP per gal per hour so at 6 GPH one at best is generating 90 HP which is 75% of 120 HP (for a 3300). I am treating this as worst case and figure anytime it won't nicely lean to 6 GPH or under, it has to run at the rich settings. For a Jabiru, I then follow their recommendations and set the mixture for 1250 F max. Even that is a moving target as it changes as one gains altitude. On 10/23/2010 5:58 AM, Lynn Matteson wrote: > > Bob- > Just to clarify, when you said: " If you want to use more than > seventy-five per cent power, you need to run at least 150, preferably > 250 degrees F above peak EGT. At those higher power settings, we need > the extra fuel to slow the burning rate so that we can avoid > detonation," I'm sure you meant to say **150, preferable 250 degrees > richer (or cooler) than peak EGT** didn't you? > > Mark, Bob, and others- > > Where are you getting the figures for the percentages of power? > Everybody talks about these percentages, but I don't see the flows, > the manifold pressure numbers, or whatever the criteria is for > establishing these percentages written as it pertains to the Jabiru > line of engines. > > > Lynn Matteson > Kitfox IV Speedster, taildragger > Jabiru 2200, #2062 > Sensenich 62"x46" Wood (summer) > Electroair direct-fire ignition system > Rotec TBI-40 injection > Status: flying...1054 hrs (since 3-27-2006) > > -- Mark Hubelbank NorthEast Monitoring 2 Clock Tower Place Suite 555 Maynard, MA, 01754 - USA mhubel@nemon.com 978-443-3955 ________________________________ Message 4 _____________________________________ Time: 04:47:41 PM PST US From: BobsV35B@aol.com Subject: Re: JabiruEngine-List: Temps Good Evening Mark, I think your 15 HP per gal of fuel is a good number for an engine with a compression ratio of at least 8.5 to one if it also has very good fuel distribution to each cylinder. If there is any unbalance in the amount of fuel per cylinder, that ideal power per gallon of fuel cannot be reached. Lower compression ratios will mean substantially less horsepower for each gallon of fuel used. One simple way of checking for balanced fuel mixtures with a fixed pitch propellor is to lean for a drop in RPM. Starting at full rich and leaning the engine should result in a slight increase in RPM. once the peak RPM is reached, further leaning will cause a drop in RPM. For an engine the size and RPM range of the Jabiru, a drop of at least one hundred RPM before any roughness is noted signifies good distribution. With excellent distribution, the rpm drop could be a couple of hundred RPM. If you can discern no increase in RPM before roughness ensues, The distribution stinks and you will get way less than 15 HP per gallon of fuel. The Jabiru that I fly has a Bing carburetor and we have no way of manually adjusting the mixture. Any changes have to be done by changing out the fuel rods and jets. There is no easy way to analyze the Bing equipped Jabiru, but with careful analysis of a good six cylinder engine monitor, some conclusions can be reached. It is NOT a simple process. It would not be at all unusual for an engine equipped with a Bing to develop as little as ten HP per gallon of fuel. I envy Lynn's adjustable mixture capability! As Always, It All Depends. Happy Skies, Old Bob In a message dated 10/23/2010 4:40:43 P.M. Central Daylight Time, mhubel@nemon.com writes: --> JabiruEngine-List message posted by: Mark Hubelbank Lynn, I don't have a manifold pressure indicator yet so I am going by fuel burn. At best a spark ignition engine generates 15 HP per gal per hour so at 6 GPH one at best is generating 90 HP which is 75% of 120 HP (for a 3300). I am treating this as worst case and figure anytime it won't nicely lean to 6 GPH or under, it has to run at the rich settings. For a Jabiru, I then follow their recommendations and set the mixture for 1250 F max. Even that is a moving target as it changes as one gains altitude. On 10/23/2010 5:58 AM, Lynn Matteson wrote: > --> JabiruEngine-List message posted by: Lynn Matteson > > Bob- > Just to clarify, when you said: " If you want to use more than > seventy-five per cent power, you need to run at least 150, preferably > 250 degrees F above peak EGT. At those higher power settings, we need > the extra fuel to slow the burning rate so that we can avoid > detonation," I'm sure you meant to say **150, preferable 250 degrees > richer (or cooler) than peak EGT** didn't you? > > Mark, Bob, and others- > > Where are you getting the figures for the percentages of power? > Everybody talks about these percentages, but I don't see the flows, > the manifold pressure numbers, or whatever the criteria is for > establishing these percentages written as it pertains to the Jabiru > line of engines. > > > Lynn Matteson > Kitfox IV Speedster, taildragger > Jabiru 2200, #2062 > Sensenich 62"x46" Wood (summer) > Electroair direct-fire ignition system > Rotec TBI-40 injection > Status: flying...1054 hrs (since 3-27-2006) ------------------------------------------------------------------------------------- Other Matronics Email List Services ------------------------------------------------------------------------------------- Post A New Message jabiruengine-list@matronics.com UN/SUBSCRIBE http://www.matronics.com/subscription List FAQ http://www.matronics.com/FAQ/JabiruEngine-List.htm Web Forum Interface To Lists http://forums.matronics.com Matronics List Wiki http://wiki.matronics.com Full Archive Search Engine http://www.matronics.com/search 7-Day List Browse http://www.matronics.com/browse/jabiruengine-list Browse Digests http://www.matronics.com/digest/jabiruengine-list Browse Other Lists http://www.matronics.com/browse Live Online Chat! http://www.matronics.com/chat Archive Downloading http://www.matronics.com/archives Photo Share http://www.matronics.com/photoshare Other Email Lists http://www.matronics.com/emaillists Contributions http://www.matronics.com/contribution ------------------------------------------------------------------------------------- These Email List Services are sponsored solely by Matronics and through the generous Contributions of its members.