lml@lancaironline.net Mailing List Archive

<<<<<<<<<<<<<<<<--->>>>>>>>>>>>>>>> << Lancair Builders' Mail List >> <<<<<<<<<<<<<<<<--->>>>>>>>>>>>>>>> Had an interesting conversation this last friday. Was on a long flight side by side with a long time A&P, that performs all maintenance on piston engines and PT-6 turbines for over 10 years. I approached him about lean of peak operations, asking his opinion on the matter. He told me he performed testing that showed lean of peak operations to cause holes on piston heads and to burn valves. I asked if he had any data on the quality of fuel distribution between cylinders on those engines. He wasn't aware of that concept. They just started doing testing on Gamijectors recently and he doesn't have firm data yet. He agreed that their lean of peak operations never involved leaning beyond 50 degrees lean of peak, nor that they had all cylinder engine monitoring packages to see what was happening on the other cylinders except for the one that has the EGT/CHT probe. Umm, this reinforces the fact that people (understandably) keep bad situations in mind. It's normal for people to be scared of damaging very expensive engines. However, as those people aren't scientists, they don't qualify all details around the issue, they just mentally label it a no-no zone... And that's all they normally pass ahead, namely their impressions on the subject. If I understand the stuff behind CHT/EGT probes, they're installed on the hottest cylinder for rich of peak operations. This means that other cylinders are likely to be running richer (on the rich of peak side, richer=cooler). Now when you go lean of peak (where richer=hotter, leaner=cooler), and you got one cylinder lean of peak, and the others are richer, hence HOTTER. Humm, wouldn't that explain why people get burned valves when operating only 50 degrees lean of peak without good fuel distribution ??? If they only went 100 or more degrees lean of peak (if the engine doesn't go rough before that), now they should have all cylinders lean of peak. Of course there are other variables like the uneven cooling airflow through the engine, which makes those conclusions questionable I grant. I showed him the articles on lean of peak on engines with gamijectors, he was definitely shaken by the stuff in those articles. He said he'll look those up to get a better opinion on the subject. Another very interesting finding from the articles is that the leaner the mixture, the longer it takes to burn. Visualize the fact that the pistons are cyclical movement. If you had combustion pressures at it's max right when the piston are at its top position, you wouldn't have any useful power being generated, while the best position to capture the mechanical force of combustion is at 90 degrees past TDC (top dead center). Because today we're stuck with a fixed combustion point (usually 18 degrees before TDC), the leaner the engine runs, the more mechanical power of the combustion is going towards generated power. LML website: http://www.olsusa.com/Users/Mkaye/maillist.html LML Builders' Bookstore: http://www.buildersbooks.com/lancair Please send your photos and drawings to marvkaye@olsusa.com.