Design RPM, 0.090ci comp ignition

[kspringer80]

I'm designing a compression ignition from scratch and find myself working on the porting. I'm trying to hit some very specific time area values but find myself scratching my head when it comes to design speed. I'm going with a 0.48in bore and 0.50in stroke, initial port time area calculations have been done at 9000rpm. As I've never designed or built one of these before I'm looking for some input on what speed I should expect this engine to run at.

 

[Tin Falcon]

I read your intro. Thanks again for posting it. And I know you do not want to be lectured about building a proven design first . Hopefully some of the guys who have designed and built ICS will chime in and help.

learning to build engines and learning to design engines two different skill sets.
Learning's to two at the same time IMHO a challenge to say the least.
Tin

 

[mu38&Bg#]

1.5CC diesel in the model airplane world run anywhere from I'd guess 6k on the low end all the way up to 25k. A sport engine would probably run about 10-11kRPM with an 8x4 prop.

Greg

 

[kspringer80]

I've been building (not from scratch) and maintaining a full race Alpha 2000 engine circa 1974 with a "great" SPICA fi system for 7 years. Also a pretty decent machinist and took an IC engine design concentration in school 10 years ago. I thought I was keeping things simple by keeping the ignition system out of this one

 

[kspringer80]

Thanks Greg, I may bump the calculations to 9.5k and see where that leads. I've got some freedom with the exhaust and intake, but trying to keep the transfer to 0.00095 sec-cc/cm3 is proving to be a challenge. My thought was to design for 9k, get it broken in then play with prop size to get the engine running at the design speed.

 

[mu38&Bg#]

If you fly models and intend to fly this engine keep in mind that RPM increases substantially in the air. Start with a 7x4 run it rich and undercompressed for break-in. Then switch to to the larger prop and slowly lean and increase compression until it holds peak settings without sagging. Do you have experience with model diesels?

Greg

 

[kspringer80]

I really have no intention of flying this one, but it might happen. This is more a technical exercise in design and fabrication. I need another hobby like I need another hole in my head! I've seen some small diesels run, but have never done it myself. I could have started out by building an existing design, but that takes a lot of the fun out of it for me.