Re: [pop-pop-steamboats] Our new members
- Quoting Donald Qualls <silent1@...>:
> brian458666@... wrote:Yes, I had completely forgotten about the stovetop variety and was going
> >> There are actually a couple valveless pulse jets that are even closer to
> >> a pop-pop in operation;
> > Yes, and I had a moment of illumination just now as I was loading up
> > coffee maker...although it does use a check valve, and the older style
> > percolators used a restricted inlet to work.
> > Brian
> I've got a stovetop type percolator that has a very broad, flat funnel
> covering the base and feeding into the vertical pipe, with liquid flow
> under the funnel permitted only through a couple tiny openings or under
> the edge if a pressure pulse should lift the pipe and basket clear of
> the pot base. The electric percolator I used to own had a rather tiny
> boiler chamber, roughly hemispherical, under the base of the pipe, and
> again a couple small openings to admit liquid. To my eye, they depend
> on the bulk of liquid in the pot being fairly well below boiling, so it
> takes a few seconds (even when the pot has begun to perk) for inflowing
> liquid to boil, after which rising bubbles push liquid out the top of
> the pipe; as the coffee heats, bubbles push smaller and more frequent
> slugs of liquid into the dome to drip through the grounds until the pot
> stops working at all when the liquid is very close to boiling -- just
> steam comes up the pipe, because the liquid can't fill the working
> chamber, much less the pipe, before it boils.
> An automatic drip coffee machine (a la Mr. Coffee) works similarly but
> with a limited supply of water; mine seems to have an unrestricted
> intake from the tank, and depends on the temperature of the water supply
> to regulate the rate of boiling, which in turn regulates the temperature
> of the water that gets poured into the grounds basket. It's a little
> topsy-turvy, though; start with water that's too warm and you'll get
> mostly steam and poor flow through the pipe, while starting with icy
> cold water gives the best coffee because you get good slugs of water and
> they heat up just right before the hot spot boils and pushes them
> through. This pot, however (mine's a Melitta), seems to depend strongly
> on the inertia of water in the tank as well as on heating most strongly
> near the intake to produce a useful pumping action. I didn't see
> anything I could identify as a check valve when I had it apart for
> cleaning after a period of disuse...
with the electric ones only. Most of the electric percolators used a small
boiler of under an inch in diameter that was at the very bottom of the pot. I
haven't seen or used one of those in many years and further details are elusive
now, and my Mr. Coffee type devices get a lot of use. It seems that each
manufacturer incorporates their own flaws so my standard backup is a french
press. But all of mine have check valves molded into the bottom of the
- brian458666@... wrote:
> It seems that eachI'll have to go look at mine; I couldn't get some pieces apart (they
> manufacturer incorporates their own flaws so my standard backup is a french
> press. But all of mine have check valves molded into the bottom of the
seem to be assembled with one-time latch-in parts, you'd break them
before they'd fully disassemble), so it's very possible it has a check
valve I missed. That would make a lot more sense in terms of avoiding
bubbling back up through the tank, and it would only need a small
plastic ball trapped in the joint between two pieces.
If, through hard work and perseverance, you finally get what you want,
it's probably a sign you weren't dreaming big enough.
Donald Qualls, aka The Silent Observer http://silent1.home.netcom.com
Opinions expressed are my own -- take them for what they're worth
and don't expect them to be perfect.
- i was also looking into the possibility of using pulse-jet designs to improve on putt-putt engine work and was considering that it might allow for a faster engine cycle and quiet running from the lack of a diafram might allow more speed
--- In firstname.lastname@example.org, Donald Qualls <silent1@...> wrote:
> David Halfpenny wrote:
> > ----- Original Message -----
> > From: "Donald Qualls" <silent1@...>
> >>> There: the fundamentals of Mechanical Engineering on a postcard!
> >> Well, at least as it stood ca. 1900, when internal combustion wasn't yet
> >> a major player in the prime mover game.
> > OK then: An Infernal Confusion engine:
> > - compresses a lump of air,
> > - heats it up a lot
> > - expands it (providing a power stroke)
> > - lets it escape along with the products of combusion (which may also
> > provide a reaction thrust)
> Of course, this cycle, like the Rankine, can be used either in "batch"
> mode or in "continuous" mode. Common piston, rotary, and pulse-jet
> engines operate in pulsed or "batch" mode, where a discrete "lump" of
> working fluid goes through the entire cycle independent of other
> charges, while ramjets, turbojets and turbofans and at least one variant
> piston engine (an internal combustion version of an elbow engine)
> operate in continuous mode, where all parts of the cycle operate on a
> flowing stream of working fluid (rather like the difference between pot
> distillation and a distillation column, or lab synthesis vs. an
> industrial process).
> > The one closest to the pop-pop is the pulse-jet or doodelbug engine, which
> > also uses an oscillating column of fluid in a backwards-pointing tube. (My
> > parents weren't very fond of these as they were married in London in August
> > 1944.) In this case, the resonant pressure wave opens and closes the air
> > inlet valve, sucks in and atomises the liquid fuel and compresses the
> > ingested air. Ignition is usually by contact between the explosive mixture
> > and the hot walls of the combustion chamber.
> > The result is very simple and powerful model boat engine that is several
> > decibels noisier than a pop-pop
> The classic valved pulsejet actually has a front intake and almost
> entirely one-way flow, and model airplane versions have a venturi
> carburetor built into the intake at the forward end (the German design,
> too large to work well with a flat reed valve, incorporated the fuel
> delivery into the grid that held the valves, so didn't as much resemble
> a simple venturi carburetor).
> There are actually a couple valveless pulse jets that are even closer to
> a pop-pop in operation; all compression and flow control is due to
> pressure pulses in resonance with the pipe, and both pipe openings face
> backward and produce thrust (though the designs I've seen have them
> different lengths and the overall flow is from the shorter pipe to the
> longer; there has to be some directional flow to keep drawing in fresh
> air and fuel and removing combustion products, of course, but it could
> be worth testing to see if this would be the case with our kind of
> pop-pop, since tuning the tubes to product directional flow has the
> potential to greatly increase the efficiency of the engine). The
> resonance frequency in these, in hobbyist scales, tends to be in the
> mid-upper audible range, leading them to produce a very distinctive
> screaming sound in addition to the usual loud roar of any jet exhaust.
> > David 1/2d
> > There are one or two additional details, but the core science behind post
> > mediaeval Mechanical Engineering isn't mechanics, or mechanisms, or
> > materials, important as they all are: it's thermodynamics.
> Yep, pretty much anything invented since James Watt improved the pumping
> engine at the mine where he worked (by inventing, out of laziness, an
> automatic valve gear to replace the continuous attention of a boy)
> depends on thermodynamics, at least until you start getting into
> practical electricity in the late 19th century. At that point,
> Maxwell's laws of electromagnetism become the important ones...
> If, through hard work and perseverance, you finally get what you want,
> it's probably a sign you weren't dreaming big enough.
> Donald Qualls, aka The Silent Observer http://silent1.home.netcom.com
> Opinions expressed are my own -- take them for what they're worth
> and don't expect them to be perfect.