David Billington wrote:

Ed Huntress wrote:
"jeff_wisnia" wrote in message
eonecommunications...

Ed Huntress wrote:


"Ignoramus10802" wrote in message
...


On 2009-10-29, ATP* wrote:


True. Yet I still hear this type of "reasoning" all the time. Should be
a
simple concept even for the technically challenged, for example, people
who
argued here that you can compress air and allow it to expand (while
doing no
useful work) with no loss of energy.

That would be almost possible if compressing and expanding was done
very quickly, before compressed air cools.

i

But it has to be done *awfully* quickly. That's why there's a minimum
cylinder size for diesel engines -- something like 300 cc. Below 3,000
rpm or so, the compressed air cools too quickly to ignite the fuel. And
heat transfer gets worse as compression goes up.


That statement may not be entirely correct, Ed.

Remembering waaaay back to my childhood playing around with control line
model aircraft. before the glow plug engine was developed we had but two
choices, conventional spark plug engines and diesel engines.


g I had one of those. They weren't really diesels (technically, they're
"homogeneous charge, compression-ignition engines), but that isn't the
issue, because they ignite from compression, the same as a true diesel. The
issue is that they use ether for fuel, or an ether-diesel mix in the larger
ones, and ether has a cetane rating of 86. Diesel fuel runs around 40 - 45
cetane. Those little engines can't produce enough heat from compression to
ignite diesel fuel.


The diesels were never very popular, but they are still being made for
thos who want to add a bit of "authenticity" to replicas of vintage model
aircraft. Those are surely far below 300 cc, but the fuel they burn may
not be quite the same as what cars and trucks use. G

http://www.eifflaender.com/enginepics.htm

I also remember my not terribly successful efforts at flying RC models
back then. My ham ticket let me do that legally on 28 Mhz (the 10 meter
ham band) using a one tube receiver in the plane which triggered a rubber
band energized "escapement" that moved a combination rudder-stabilizer at
the rear of the plane.


A tail-wagger. I built one of those, a Cessna Birddog from a kit, with an
.049 Babe Bee engine. I used a salvaged CB walkie-talkie for a transmitter
and a homebrew superregen receiver. The signal was CW. I made the escapement
from a tin can, with bits of HSS hacksaw blade soldered onto the tips of the
arms. It flew pretty well, but I was not much of a pilot. Fortunately, if
you just tossed the transmitter aside, it would land by itself.


How the heck I just remembered that the tube used in those receivers was
an RK61, a gas filled triode, I'll never understand.


For the same reason that I remember that my first homebrew regen receiver, a
battery-powered rig that I built in 1957, used a 1T4. Our memories of old
stuff tend to hang in there while we forget what we had for breakfast. d8-)


http://tubedata.milbert.com/sheets/138/r/RK61.pdf

Thaks for the mammaries though.

Jeff


sigh That's most of what I'm good for these days. Sometimes I feel like an
antique. d8-(


A small diesel here
http://www.model-engineer.co.uk/albu...=6778&p=123122
, about 28cc, not sure about the relation of lamp oil to pump diesel but
it sounds less volatile than the small "diesel" aircraft engines I used
on occasions which were a blend of ether, caster oil and amyl nitrate.
Last time I used one was about 1981 and on returning to the US from the
UK I asked my chemistry teacher about getting some ether to blend my
own and she almost had a fit, then gave me a lecture about the dangerous
nature of ether. Didn't know then that engine start spray is mostly
ether and have seen a thread elsewhere where a chap detailed using it to
refill a capillary temperature gauge, Lucas IIRC.

I believe "lamp oil" is deodorized kerosene K1, pretty much like
"winter" diesel D1.