A very incomplete history of gas turbines is added.
Heating a flammable liquid to its boiling point and using the
heat of the burning vapour to evaporate even more of the liquid
can obviously lead to a chainreaction.
We give the values for ethanol (85%).
In first appoximation Q(t)=Q(0) for t
t0 and for t
Where t0 is the moment the boiling sets in
is the efficiency of heat transfer, C is the calorific value
and E the heat of evaporation
(approx. 260 cal/g)
So with only 9 % feedback we have an exponentially growing heat output
tE/C) on a time scale of ½ second.
In other words a spectacular flame leaping from the chimney.
As with every exponential growth, non-linear effects restrict the chainreaction.
Very soon the internal flame get choked. Despite the chimney effect, not enough air can reach
the outpouring vapour and most of the action is outside the apparatus.
This is however a temporary effect and after a few seconds the next
blast will emerge.
It may take upto 5 minutes before the show starts, but in a couple of seconds
all fuel is consumed and the apparatus is left to cool down.
Spectacular as a demonstration is, there have been half a dozen public demo's,
it is not dangerous provided a few safety precautions are taken into account.
Perform the demo outdoors on a free and flat stone platform.
Keep a safe distance once the preheater is ignited and the chimney is placed.
look into the chimney, for instance when you think the apparatus is failing.
Wind may extinguish the preheater, but a windscreen can prevent that.
Do not use other fuel than 85% vacuum distilled ethanol (*).
This will burn safely and leave no residue.
Do not scale it up.
I use 60 ml ethanol and the same amount in the optional afterburner.
Soft solder can not be used in the construction.
I used stainless steel and hardsoldered brass.
Tin cans for the chimney can be reused.
The internal diameter of the C-shaped pipe should be large enough to prevent
pressure building up in the fueltank.
(*) Approximate values for other fuels:
The design of the apparatus is modular. This allows easy variation
of aeration and chimney height.
An ethanol flame is barely visible in daylight. Applying a bit of grease
to the inside of the chimney solved that "problem".
Note the blue flame from the afterburner.
Using a fan
With an electric fan we can more or less prevent the choking effect.
The result is a hissing flame and a shorter burning time.
NAC 2011 festivities
To celebrate the 90th birthday of Prof. Kees de Jager
the chainreaction was, after a short explanation, demonstrated during
the 'Nederlandse Astronomen Conferentie 2011' on the island of Texel
on May 19 2011.
To celebrate the 65th birthday of Els Wegdam
the chainreaction was, after a short explanation, demonstrated
in front of
in Utrecht on June 22 2014.
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The V1 was a flying bomb powered by a pulse jet engine.
The fuel in flight was gasoline.
Click in the picture for the full resolution version (2096x1156).
As the construction of the pulse jet engine is simple and well known, a number
of people or groups have rebuild the engine for fun.
However the original design was intended to bomb London and other cities in Southeast England.
The lifetime of the inlet valves is limited to less than an hour (~100000 movements @ 45 Hz).
V1 on YouTube
There are numerous videos on YouTube about the V1, historical footage as well as post-WWII reconstructions.
Before and during WWII gas turbines were developed in the USA, Germany and the UK
which could be used for turbo-prop and jet-airplanes.
The most elegant design is the Rolls-Royce Derwent gas turbine
which powered the twin-engine Gloster-Meteor.
Click in the picture for the full resolution version (8512x4896).
A drawing of the thermodynamics of the Derwent from
A.J.C. De Lang & L.Suetens,
Toegepaste technische warmteleer. Click in the picture for the full resolution version (2476x1292).
A: 4 inlet ducts
B: impeller of compressor
C: 9 diffusor channels
D: 9 combustion chambers
E: turbine, 48 fixed and 54 moving blades
F: jet exhaust duct
G: connection shaft
H: cooling fan
from G. Geoffrey Smith M.B.E.,
Gas Turbines and Jet Propulsion for Aircraft,
can be read
Hear the sound of the Derwent (wav).
the clutch of the auxilary engine
rotating at low speed by the auxilary engine
first fuel injection
speed up to full power
the second half (17.6 s) is the reverse of the first half.
On 7 November 1945, the official
air speed record by a jet aircraft was set by a Meteor F.3 at 975 km/h (606 miles
per hour). In 1946, this record was broken when a Meteor F.4
reached a speed of 991 km/h (616 mph). This record was again broken by
testpilot Roland Beaumont in 1946 with a speed of 1047 km/h.
In 1947 the Soviet Union bought (with approval of the British government!)
Derwent and Nene engines from Rolls-Royce. They were copied for the
(Mikoyan-Gurevich) jet fighter aircraft
Stalin and the Bomb