Elektra II First Test Run

[larry cottrill]

Gentlemen –

Well, last night after dark, with my son Jonathan on the camcorder, I was finally able to try her out. Using the shop vac as my air source, I was not able to get sustaining operation; however, I did get lots of good roaring pulse combustion and several interesting observations that I think are worth noting.

GENERAL OBSERVATIONS

It is possible to get pulsating combustion over a very wide range of forced air input levels and fuel settings; seemingly, the widest range of variations I have yet observed, although this is obviously subjective. Though the engine did not self-sustain, the slightest trickle of air is sufficient for good combustion. On the other hand, good roaring was also attainable at the maximum air volume, without ‘blowing out’. So, the design is at least capable of handling a wide range of conditions [if we can extrapolate this observation over into sustaining operation].

The frequency of operation is definitely higher than observed on the Elektra I, and does not vary appreciably with changes in air input or engine temperature. This apparent high stability of frequency was noted in testing the Elektra I, but was not true of the Fo Mi Chin engine [where the intake impedance is significantly higher]. It sounds to me to be somewhat higher than the Dynajet when that engine gets good and hot, but this is just a subjective judgment, not verified. The pipe of that engine is about ten inches [254mm] shorter than the Elektra II, of course.

It was easy to get pulsing combustion either by aiming the air straight down the intake or by aiming at the intake flare from slightly above or to one side. The principle difference observed is that when you’re attacking it straight down the chute, you get a heck of a kick back from the intake, both in the case of individual bangs and in strong pulsing operation. So, this “pressure waveâ€

[Bruno Ogorelec]

Well, congratulations are in order first of all. You seem to be going places with this engine type. It is obviously on the verge of self-sustaining.

All my comments are coming from a man with no practical experience and must be taken with a pound of salt.

So, for what it's worth...

I don't think throttleability will be easily achieved in this engine. An educated hunch tells me it will be an engine with a certain mode of operation all of its own. Why do I think that? Because there's no real leeway for the combustion zone to change. It is more or less set by the engine shape. In a conventional can-shaped chamber with ports at top and bottom, the combustion zone can move, stretch and shrink, and thus respond to varying inputs. In contrast, Elektra generates a kind of vortex in its flat drum that probably stays more or less the same whatever you do. The sharp transition to 'proper' mode is to me a strong indication of this.

While I am quite impressed with Elektra, I must confess to being slightly baffled by its disposition of the intake and exhaust ports. (But then, I am also baffled by the Chinese engine.) I can see no good reason for them to be where they are, even after reading your description. Usually, engine insides are shaped to conform to the expected (or desired) flow patterns. I can see no benefit to the particular flow pattern I imagine I can see within the engine, either during the intake or during the exhaust phases.

I think that -- at some point in the future, should you be disposed towards it, you should check whether the convergence of the intake and exhaust streams is beneficial or detrimental. Given that the proportions of the engine are proven to be conducive to self-sustained operation, I think it would be hugely educational to build an engine with the same components but with a different disposition of ports.

To my mind, the layout illustrated here make more sense. But then again, I have limited practical experience and it is easy enough to draw squiggles on paper...

[Ray(in England)]

Larry,
U deserve praise for building so many experimental designs.
Very few contributors do, I'm the worst offender for that!.
Hope u can get one self sustaining soon. Good luck.Ray.

[Graham C. Williams]

Dear Larry.
Congratulations once again.
My first thought would be to increase the air speed in the induction tube. Do a Kazoo and squash it a bit just behind the intake flair. Perhaps your idea of increasing the intake flair will achieve the same effect.
The overall length of the induction pipe may also be a bit short. A length of thin wall pipe pushed up the inside of the induction pipe might do the job.
My thinking? Injecting air does 2 things: increases the mass of charge and slightly increases the time it takes for the combustion-damping wave to return to the combustion chamber.
A longer induction pipe can reduce the charge density but increases the confinement and available combustion time.
What ever it is you cannot be far away.
Best regards
Graham.

[larry cottrill]

Gentlemen -

Thank you, thank you. Graham, a little pinching of the intake pipe actually fits in with my plans fairly well, a bit later on -- because if I get this thing running well on vapor, the next phase of the plan is to develop a venturi and needle valve carburetion geometry for liquid fueling!

So, maybe this is the time to try some tube flattening to see if that does anything for me. I need to think a while on making such a 'radical' change, though.

Thanks!

L Cottrill