There has been a lot of work recently on free piston engines. Cant point you in the right direction right now, but the Fluidyne was one of the most efficient and is still used from time to time. Engines using solid (non liquid) pistons seem less popular, but I have come across some references to them. Alan ----- Original Message ----- From: "R.L. Roebuck" <rlr20@xxxxxxxxxxxxxxxx> To: <modeleng@xxxxxxxxxxxxx> Sent: Wednesday, November 21, 2007 9:43 PM Subject: [modeleng] The wife, explanation of SWMBO, and free piston engines She Who Must Be Obeyed [if you want to want to keep the model engineering budget at it's optimum level]. Anyone know anything about free piston engines? I've got someone here asking about them. I've found a few things on the web... http://www.ee.kth.se/php/modules/publications/reports/2005/IR-EE-EME_2005_003.pdf ...but I'm curious as to whether it's an old concept rehashed with some modern kit fitted to it. Yours, Rich (31; wife, just turned 29. Wife says I have the bald head of someone who who is aged 131.) On Wed, 21 Nov 2007, Patrick Coppens wrote: SWMBO" ???? what the h#&& is that? MODEL ENGINEERING DISCUSSION LIST. To UNSUBSCRIBE from this list, send a blank email to, modeleng-request@xxxxxxxxxxxxx with the word "unsubscribe" in the subject line. -- No virus found in this incoming message. Checked by AVG Free Edition. Version: 7.5.503 / Virus Database: 269.16.2/1142 - Release Date: 20/11/2007 17:44 MODEL ENGINEERING DISCUSSION LIST. To UNSUBSCRIBE from this list, send a blank email to, modeleng-request@xxxxxxxxxxxxx with the word "unsubscribe" in the subject line.