Thunderchine starting problems

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Re: Thunderchine starting problems

Post by HPSCL » Fri Mar 13, 2009 12:11 am

milisavljevic wrote:Oh my, where to begin...
HPSCL wrote: Fluidity (for lack of a better word) is defined as the physical property of a substance that enables it to flow.
I believe the word you were looking for is "viscosity"; however, its definition stems from a different perspective.
Actually, neither of those two words can correctly convey my thoughts. I do agree, however, that my choice of the word "fluidity" was simply idiotic.

I had many problems getting my first homemade thermojet to start. The area of the injector opening was too large and the injector "spray patterns", were not even close to identical. The burning fuel that came out of my homemade "rosscojector" was flowing at many different angles; Against the intake tube walls, mostly. I tried filing the ends flat and making the hole uniform, but nothing worked The burrs that were left on the inside of the hole, along with an irregular shape, would always cause one side to flame-out.

I pinched one of the injector openings shut, and the engine started to rumble and with a little bit of air, it seemed to almost self-sustain. Well, no PhD was required to assume that the engine was simply getting too much fuel, even at a low line pressure...

However, I hypothesized that IF the orifice hole were indeed smaller... and the inlet pressure higher, the intake tube would draw in more air???

Years ago, on yet another forum , we were discussing how to get a 1/4" diameter stream of water to shoot well over 50 feet.
A young girl from England?, added that the nozzle shape - as well as an uninterrputed flow of water, would be the best approach.

My thought was that IF I were to have laminar flow of propane gas in the intake tube, instead of the turbulent flow, the intake tubes would draw in more air and at a higher velocity? I started with a clean end on the injector and hammered it to a long tapered point. The tip was peened over until it was closed, and then an awl was used to gradually open a hole in the center.

The engine fired and self-sustained on the first try.

HPSCL wrote: The Thunderchine has two injectors, each "a 3 point style", with three 1.5mm holes drilled in each one.
milisavljevic wrote: This is simply not true.
I beg to differ - and only because of what I read, in THIS topic:
Re: Thunderchine starting problems

Postby GRIM on Wed Mar 11, 2009 9:03 pm
Hi Zohrke , welcome ,
I am very pleased to hear there is another Thunderchine in existence...

The injectors (3 point style 5/16” od ) had 3 x 1.5mm holes drilled in each one , (total of 6 x1.5mm holes)...

milisavljevic wrote: The specification for Thunderchine contains no fuel injection system, at all. The Thunderchine that GRIM
built has the injectors you have described...the difference between generalisation and specific instance.
I realize that you included no specification of a fuel-injection system, in your design of the Thunderchine, but the need to correct me for generalisation was warranted because... I forget to include a direct quote of that statement?

HPSCL wrote: I read on this forum...that any disturbance in the flow of the incoming air, OR the exhaust, could cause a flame-out.
milisavljevic wrote: Even if someone did post this here, it is pure FUD. If any disturbance could cause a flameout to occur, then
we could never hope to start pulsejets, much less run them. Disturbance is intrinsic to pulsed combustion.
Again, I apologize for miquoting / misunderstanding that statement. It was pure FUD. (Thanks, I learned a new slang-word, today!)

It came from misreading this post, by Eric:
Eric wrote: by Eric on Fri Mar 03, 2006 8:47 pm :

Its best to not go behind the engine when it is running at full throttle or a low idle, because these are the most likely times of flameout.
..Duh! - Again, sorry!
milisavljevic wrote: We do not want laminar flow injectors. Pulsejets are not cutting torches or bunsen burners. The plume of
fuel vapour introduced into each intake must be thoroughly (and to the extent possible, homogeneously)
mixed with the fresh air "charges" transferred into the combustor during each cycle (approx. 170-180 Hz).
Propane gas, ("the plume of fuel vapour") expands to 270 times its volume, as it exits into the open air. I would agree with you that a liquid hydrocarbon (such as gasoline for example) "must be thoroughly (and to the extent possible, homogeneously)
mixed with the fresh air "charges" transferred into the combustor during each cycle".

Without a buttload of incoming air, a turbulent plume of fuel vapour results in a overly-rich fuel/air mixture in the combustion chamber. The result of which, will cause a 3 foot flame coming out of the end of the tailpipe, as the excess of propane vapour finally exits to the open air.

The exiting propane molecules are moving from a high concentration (in the fuel line) to a lower concentration (in the intake tube). A "low momentum mass transfer" of these molecules in the intake tube, is what results in turbulent flow. (The rapid variation of pressure and velocity in space and time).

If the pressure and velocity (of the exiting propane molecules) are independent from time (maintaining a higher pressure and higher velocity throughout the entire length of the intake tube, this would draw in a larger quantity of air into the intake tubes. This larger quantity of air is what is needed to thoroughly (and to the extent possible, homogeneously) mix with the propane vapour.

As you well know, propane is heavier than air (1.5 times as dense). At a low momentum mass transfer, the propane (most of it) will sink to the lowest level of the combustion chamber... Especially in a large one, such as the Thunderchine. I believe that this may just be why some large valveless pulsejet engines require a leaf blower to start. The turbulence should occur within the combustion chamber itself, much more so than in the intake tubes. The intake tubes primary function, is to suck in mass quantities of air.

My thoughts are merely an observance. My sole intention is to get a "thermojet" to transition from a low-idle, to a high/self-sustaining roar... without the need of additional compressed air. (coming out of a blow-nozzle or leaf-blower).

I feel as though I've somehow aggravated you... As though it was my sole intention to contradict an extremely well designed thermojet and propane fueling system. As I've stated numerous times, I am NEW to all of this and did not mean to step on anyone's toes.

I've been tinkering around with ignition location, fuel-delivery and fuel/air suspension for well over 5 years now, as my OTHER hobby was designing and fabricating PVC-based combustion launchers. I'm just tryin' to be a part of the thought process, on how to improve the efficiency, the power (and most importantly) the "ease-of-use" with these type of engines.

... Don't wanna change your meaning of FUD, from British to Scottish!

You rock!

Mike Everman
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Re: Thunderchine starting problems

Post by Mike Everman » Fri Mar 13, 2009 3:14 am

HPSCL wrote:snip> My sole intention is to get a "thermojet" to transition from a low-idle, to a high/self-sustaining roar... without the need of additional compressed air. (coming out of a blow-nozzle or leaf-blower).
Most thermojets start airless that way with simple tube injectors of the right size in the right place. They are the most forgiving to scale whilly-nilly, and probably the least efficient of them all. I can get most linear engines to start airless with the right size of rosscojector, but can be done with a simple hole, again, right size and location. The only ones I've not gotten to go airless are Chinese layout. Don't know why.
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Post by milisavljevic » Wed Mar 31, 2010 10:48 am


No maintenance for the original Thunderchine plans thread, or any subsequent threads, will be forthcoming.

As I am no longer a member or a participant in this forum, existing builds will be supported via email only.
If you have not already received a valid email address from me, one will be forwarded to you in due course.

Prospective builders are advised to look elsewhere for plans. If you are NOT a novice builder, I recommend
you search for pulsejet plans from that most excellent, mild-mannered of active, on-forum builders, Metiz.

no safe haven for merchant scum

for ye merchants who do the prop'r t'ing only if
ye be haul'd-up on charges b'fore ye ship-mates
an' threat'nd wit' forfeiture of all ye precious loot
hear this - so-called stand-up guys YE BE NOT

Cap'n M.

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