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Homemade hydrogen gas
generators can be as simple as tying stainless steel plates
together and electrifying them and as advanaced as a
multi-cell stainless steel hydroxy generator that can produce
a liter or two of gas per minute. There are many options
available on the internet. The biggest question that
needs to be answered is what will you be using the hydrogen
generator for and how much gas is needed? One of the
best documents Umpua Energy, Inc. has seen on the internet is
the Tero cell - and we have actually built one. It is a
fun project and the cell produces nearly two liters per minute
of hydroxy gas. Note: To avoid a run away reaction, it
is recommended that you control the amperage to the hydrogen
generator by using a PWM circuit that you can buy from several
sources within Ebay.
Electrolyzer
The electrolyzer shown
in Figure 1 is based on the common-duct
series-cell electrolyzer concept originally developed and
patented by William Rhodes, Ernest Spirig, Yull Brown and
later refined by Bob Boyce, George Wiseman, etc… It uses an
alkaline (NaOH, KOH) electrolyte to split distilled water into
hydrogen and oxygen components very efficiently.
The produced hydrogen and
oxygen gasses are not separated to separate containers, but
kept mixed. The produced oxyhydrogen gas is a stoichiometric
mixture of hydrogen (2 parts vol.) and oxygen (1 part vol.)
and can be combusted in vacuum.
The combination of series-cell
topology is very efficient, because it allows the cells to
operate as close to their optimal cell voltage (1.47V) as
possible. The electrolyzer runs fairly cool, at about 30-50 C
depending on the current and electrolyte.
The electrolyzer shown in this
report has about 80-90% total efficiency when all things are
considered (ambient temperature, ambient pressure, accurate
measurement of gas volume and current) when powered by
straight DC. Pulsing (PWM) or modulation of the input voltage
waveform could increase the performance further, as it is
known that in the beginning of each pulse larger current flows
than in the steady state condition, thus lowering the cell
voltage needed to push thru a certain amount of current and
increasing the efficiency slightly. There are also claims of
various resonance phenomena (Boyce, Meyer, etc.) that
supposedly dramatically increase the gas production rate vs.
input current when the electrolyzer is driven with a certain
type of PWM rich in harmonics. However, this author has not
been able to replicate any resonance modes in any sort of
electrolyzer.
The electrolyzer has 7 cells
with a target input voltage of about 12.9-14.1Vdc depending on
temperature. This makes the cell voltage about 1.85-2.0V.
Electrolyte in each
compartment is practically isolated from other compartments,
but there are 3mm diameter electrolyte level equalization
holes drilled in the bottom corner of each plate (staggered)
Soft transparent PVC spacers
rings
Figure 1. Series cell
electrolyzer cross-section
Electrolyzer construction
The eight electrolyzer
plates (Figure 2) are about 0.8mm thick 160mm x
200 mm stainless steel (304 grade). A 10mm gas vent hole is
drilled in each plate. The electrolyte level is always about
25mm below the gas vent hole. There are 3mm diameter liquid
level equalization holes drilled in the bottom corner of each
plate (not shown) in such a way that adjacent plates have
holes in opposite corners. Staggering and using small holes
minimizes any efficiency loss due to current leakage between
cells, but makes electrolyte refilling and level equalization
significantly easier. The two end plates have a small SS piece
welded for electrical contact. After taking the picture the
plates were sanded with an orbital sander to expose clear
metal and then cross- hatch pattern was “engraved” on the
plates with a rough file attached to a wooden block. This is
to increase the active surface area of the plates and seems
necessary for ultra high efficiency. Other methods to increase
plate area exist as well.
Figure 2. Stainless steel
electrolyzer plates (8 total)
Nine spacers
(Figure 3) were cut out of 3mm thick soft and transparent PVC
sheet with a knife. The wall thickness is 12mm. The PVC sheet
is originally designed for door material for large room-size
refrigerators. The small square PVC blocks were meant to keep
proper distance between SS plate centers, but they turned out
to be unnecessary and were not used.
Figure 3. Soft PVC spacers
rings
The end plates
(Figure 4) were cut out of 12mm thick PVC plate. The size of
the plates was 200mm x 240mm. Eight 8mm holes were drilled for
M8 size stainless steel through-bolts. A ¼” pipe thread was
tapped in a 11.8mm gas vent hole. A valve and gas hose
connector was epoxy glued to the ¼” tapped hole in both
plates. Other thread sealants may not be compatible with the
electrolyte so it’s best to use epoxy or teflon tape. The
valve was lined up with gas vent hole in SS plates. NOTE: When
the electrolyzer stack is tightened up the PVC end plates tend
to bend and bulge. Some form of metallic bracing should be
used to prevent bending or the end plates made out of thick
stainless steel plate.
Figure 4. PVC end plates with
gas valves attached
The first stainless steel
plate and one PVC spacer ring are shown in Figure
5. There is a PVC spacer ring also between the PVC end plate
and first SS plate. A 35mm piece of 8mm ID 12mm OD rubber hose
is slid over the bolts to isolate the bolts from the plates
and hold the plates in place. Note that it would have made
more sense to drill the gas vent hole to the upper left corner
of the plates, so that draining the all of the electrolyte out
of the electrolyzer would have been easier.
Figure 5. First SS plate in
place with the PVC spacer shown
A side view of the cell stack
with several SS plates and PVC spacer rings in place is shown
in Figure 6. Note the soft PVC sheet material in
the background with the cut outline drawn with a permanent
overhead transparent marker pen.
Figure 6. Partly assembled
cell stack
The finished electrolyzer is
shown in Figure 7. The two PVC end plates are
clamped together with 70mm long M8 stainless steel bolts with
Nyloc nuts. After initial tightening the electrolyzer was
submerged in hot tap water (about 60 C) with the gas vent
valves closed. This softened the PVC gaskets and allowed the
stack to be tightened up even further to provide an excellent
seal. Note that the 12mm PVC plates are quite soft and some
bulging is visible. Two additional bolts would have been
useful to equalize the bolt forces more evenly around the
plates.
Figure 7. Assembled stack
The finished electrolyzer
equipped with a bubbler is shown in Figure 8. The
bubbler is absolutely essential to prevent backfires from
blowing up the electrolyzer. The electrolyzer may be filled
with slightly acidic water (use vinegar) to neutralize any
residual NaOH vapors in the output gas. It would be wise to
use a non-return valve between the electrolyzer and bubbler to
prevent bubbler water being pushed back into the electrolyzer
in case of backfire.
Figure 8. Finished
electrolyzer with bubbler
Figure 9 shows the electrode
plates after the electrolyzer had been used for some time. The
chemical reactions occurring in the electrolyzer have slightly
darkened the electrolyte. The use of 316 SS electrodes would
probably have prevented this. Note how the other side of the
plate is relatively clean, while the other side has a darker
deposit. Note also the sanded and crosshatched electrode
surface.
Figure 9. Electrode
discoloration due to chemical reactions (NaOH & 304 SS)
Electrolyzer tips
1) Gas
production is directly proportional to the current draw only.
At STP conditions (0 deg C, 1
atm) you need approximately 1.594 Amps for each LPH per one
cell, while you need less if you measure the gas volume at
room temperature.
2) The ideal
cell voltage would be about 1.48V, and anything above it is
wasted efficiency. The lowest practical cell voltage seems to
be around 1.8V-2.0V. The voltage is only needed to push the
current thru the cell, it has no relation on the amount of gas
produced. The cell overvoltage (above 1.48V) is determined by
electrode materials, current density, electrode spacing and
conductivity of electrolyte.
3) Power or
total efficiency is defined as the amount of watts needed to
produce one LPH. Series-cell designs seem to have the best
efficiency in the range of 2.5-3 Watts per LPH. The most
efficient electrolyzer would have a large number (100) of
cells in series with narrow cell spacing (3mm) at a low
current (10A).
4) Many
people build simple single-cell car hydro-booster type
electrolyzers and control the amperage by using weak
electrolyte. The cell voltage is often around 13V, and they
put just enough electrolyte to pass 5A or so. 5A creates only
3.5 LPH of gas, so the efficiency is very bad at 18.5 Watts
per LPH. Properly designed 7-cell series electrolyzer would
produce 7 times that amount or
24.5 LPH gas at the same input power.
5) The cell
voltage is also dependent on the current density (current /
electrode area). Smaller cell area is less efficient because
it requires higher voltage to pass the same amount of amps.
Good practical current density is around 0.5A/Sq.inch or
0.1A/cm^2. The electrolyzer shown in this report had an
effective plate area of about 170cm^2, with a target current
of about 20A.
6) The
higher the current thru the cell (higher current density) the
higher the cell voltage. Power efficiency decreases as the
current increases if the plate area is kept the same. To keep
the power efficiency the same increase the plate area in
proportion with the current (keep current density the same).
7) The
smaller the electrode spacing the lower the cell voltage. In
practice 3mm electrode spacing is good up to about 10A. At
higher currents the electrolyte starts foaming and crawling up
the plates (reduces efficiency) and the electrolyzer starts
spitting electrolyte foam out. For 10-40A use 5mm-8mm spacing.
8) Best
electrolyte is NaOH (1 part NaOH 4 parts water by weight) or
KOH (28% by wt). These give the lowest practical cell voltage.
9) The best
electrode material would be nickel, but nickel plates are very
expensive. Nickel plated steel plates would also work. The
most practical electrode material is stainless steel. The
electrode surface conditioning is very important at minimizing
the cell voltage. Best to sand (crosshatch pattern) the
electrode plates to create lots of fine sharp points.
10) Bubbler is absolutely
essential to prevent backfires from blowing up the
electrolyzer. Bubbling the gas thru a water bath is the only
safe way to prevent backfires, provided that the bubbler is
strong enough to contain any backfires and that the water
level in the bubbler is high enough. Alternatively the bubbler
can have a pop-off lid or a rupture disk.
11) The electrolyzer as shown
will not be able to take any pressure without leaking. For
pressurized operation use a pressure-proof shell (metallic).
If you need to store oxyhydrogen gas for a short period of
time, put a large balloon on the bubbler lid. The balloon will
store the gas at atmospheric pressure and will not be very
dangerous if it explodes due to a backfire. Remember to wear
hearing and eye protection.
It is impossible for an
electrolyzer to be anything else than 100% Faraday efficient,
unless there are significant leakage currents between cells.
Passing one Amp thru a single cell will always produce gas at
a rate of 0.627LPH when reduced to STP conditions, no matter
how the one electrolyzer cell is constructed.
This however applies only at
STP (0 deg C and 1 atm ambient pressure). At room temperature
(25 deg C) the same amount of gas has higher apparent volume.
Substituting T= 25 deg C gives the efficiency as 0.684 LPH/A.
Stated the other way the Faraday efficiency would appear to be
about 109.5% if the gas volume was measured at room
temperature, unless the correct efficiency value for room
temperature (0.684LPH/Amp per cell) was used.
The thermoneutral cell voltage
is ~1.48 V, which means the voltage at which all input energy
for the electrolysis process comes from the electrical input
energy. At 1.23 V (reversible cell potential) part of the
energy comes from ambient heat and electrolyzer is about 120%
voltage efficient. Note that 100% efficient hydrogen oxygen
fuel cell would produce 1.23V. The thermoneutral voltage of
~1.48V is considered to be the 100% voltage and power
efficient electrolysis. Combusting the produced gas will
release exactly the same amount of energy that was used in
making the gas.
The 100% power or wattage
efficient electrolyzer would consume 1.48 V * 1.594 Ah/l =
2.36 W/LPH when gas volume is measured at STP. At room
temperature the 100% efficiency is 2.16W/LPH.
In the literature the
electrolyzer efficiency is usually defined as the ratio of the
thermoneutral voltage (1.48V) to the cell voltage. At 2.0V
cell voltage it would imply a total efficiency of 74%. This
also shows the inefficiency of single-cell hydro-booster type
electrolyzers operating at automotive voltages (~12-14V),
leading to a total efficiency of about 10%.
Series-cell electrolyzer
voltage and current measurements
The current thru the
series-cell electrolyzer is extremely sensitive to the voltage
across it. This is because the electrolyzer acts as a very
non-linear resistance, with pn-junction like characteristics.
It takes a certain cell voltage until the current starts
flowing (“knee voltage”) and increasing the cell voltage above
this voltage will increase the current
exponentially. Figure 10 shows measured and
modelled electrolyzer current vs. voltage graph for the 7-cell
series electrolyzer. Note how increasing the electrolyzer
voltage from 13.2V to 13.9V (5%) will cause a five-fold (500%)
increase in current (from 2A to 10A).
Electrolyzer current vs voltage
7-cell
series-cell electrolyzer
Electrode area = ~170
cm^2, gap = ~3mm
Figure 10. 7-cell series
electrolyzer current vs. voltage
Note that even the insertion of a current
meter in series with the electrolyzer may cause high enough
voltage drop that significantly reduces the electrolyzer
current. Thus it is absolutely essential that the current
meter is in place when the electrolyzer gas output rate is
measured.
This extremely non-linear resistance of the
electrolyzer also causes the current thru the electrolyzer to
be modulated very strongly with any small changes in the
electrolyzer voltage. This is especially true if the
electrolyzer is powered by rectified AC, for example from a
transformer based battery charger or power supply.
The oscilloscope pictures of the 7 -cell
electrolyzer voltage and current waveforms are shown
in Figure 11. The power supply was a mains
transformer followed by a bridge rectifier and a large
filtering capacitor. Note how the electrolyzer voltage (trace
2) has a small ripple on top of it, which causes the
electrolyzer current to be modulated between zero and peak
current (trace 1), with appearance similar to half-wave
rectified AC. The current draw waveform may be easily measured
with oscilloscope by connecting the oscilloscope probe across
the multimeter terminals wired in series with the electrolyzer
in the current measuring mode. Thus the oscilloscope shows the
voltage drop across the multimeter current shunt resistor.
Figure 11. Series-cell electrolyzer voltage and
current waveforms
The pulsed current waveform causes significant
measurement inaccuracies if normal digital multimeters or
analog current meters are used. Normal current meters respond
to either straight DC or perfectly sinusoidal AC waveshapes
correctly, but show significantly lower current values for
pulsed DC type waveforms. True-RMS multimeter is required to
measure pulsed waveforms correctly (the RMS value represents
the equivalent “heating value” of any current or voltage
waveform). Figure 12 shows comparison between
current readings of an analog current meter and a Fluke
True-RMS multimeter, while measuring current draw of the
7-cell electrolyzer powered by a transformer -based power
supply (actual current waveform as shown in Figure
11). The analog current meter shows approximately 7A while the
correct RMS value is 10A, which would cause the electrolyzer
to appear 143% efficient based on the analog current meter
reading which is not true!
Figure 12. Comparison between current meter
readings for pulsed electrolyzer current
For the most accurate measurements straight DC
should be used, preferably from a battery which is not
connected to a battery charger. If any other power supply is
used, True-RMS measurement equipment is needed for accurate
results.
Series-cell electrolyzer current limiting
As the series-cell electrolyzer has very non-
linear voltage vs current characteristic, it is important that
some form of current limiting is used to prevent current
runaway. While the electrolyzer is operating it will get hot
and heat will decrease the required cell voltage to pass a
certain number of Amps, thus increasing the electrolyzer
current draw if the electrolyzer voltage remains the same.
This is likely to increase the current draw very
significantly, which may cause electrolyte boiling and other
problems.
PWM
current limiting
The best way to limit the current is to use PWM
or pulsed DC and to adjust the duty cycle to maintain the
average current. A fairly straight forward way is to use a
Hall effect current transducer (such as LEM LTS25-NP), which
outputs a voltage proportional to the current and use this as
a feedback to a PWM controller chip (TL494) to adjust the PWM
duty cycle. For the switch FET IRFZ44 (N-channel 17.5m? 49A,
placed between electrolyzer negative and ground, switched on
with positive voltage) or IRF9Z34 (P-channel 140m? 18A, placed
between electrolyzer positive and battery positive, switched
on with negative voltage) may be used.
For the PWM controller a ready
made DC motor speed control unit will do fine. It usually has
a potentiometer to adjust the duty cycle, which can be
replaced by circuitry to automatically adjust the duty cycle
based on measured current draw. If automatic set-and -forget
operation is not required, the PWM controller may be used to
control the electrolyzer current draw manually.
For most accurate current limiting the RMS
current value may be calculated with for example MX536A or
AD536A True RMS-to-DC converter chips.
For minimum parts count a microcontroller (e.g.
Atmel AVR series) may be used with the Hall effect transducer
output routed to the AD converter input and the duty cycle
adjustment and RMS current calculation performed in software.
The switch FET may be directly driven with the
microcontroller.
Capacitive current limiting
Capacitive current limiting (Figure
13) may be used for electrolyzers powered by rectified AC. It
is based on putting a capacitor in series between the AC
source and the bridge rectifier. The reactance of the
capacitor will limit the current to a certain value, but will
not dissipate any power like a current limiting resistor.
The capacitor must be suitable for AC use (not
an electrolytic capacitor). For mains-powered operation power
-factor correction capacitors are the best. This is best
suited for welders operating on mains power (no heavy
transformer needed) or hydroboosters running on modified
alternators (diodes removed). You can use any number of cells
(even one), but you need to figure about 2.0V per cell
minimum. For 230VAC 50Hz you need about 14uF for each Amp.
Figure 13. Capacitive current limiting
Output measurements:
Run #7: (3rd Aug 2005)
Electrolyte drain-cleaner grade 93% pure
Potassium Hydroxide or KOH pellets in medical grade purified
water. Concentration 28% KOH and 72% water by weight. 500
grams of electrolyte (about 450ml volume) was mixed and poured
into the electrolyzer. The electrolyzer was allowed to run
without collecting gasses for a few hours. During this time
the electrolyte temperature stabilized at 45C while the
ambient temperature was 17C.
The gas production rate was measured by
collecting the gas in a 0.5L coke bottle filled with water.
The weight of the bottle with water was measured. The bottle
filled with water was turned upside down while partly
submerged in a cold water bath. The gas was allowed to bubble
through the water bath to the bottle and the time was
measured. After removing the gas hose and stopping the timer
the cap of the bottle was screwed on while still under water
and the weight of the bottle filled partly with water and
partly with gas was measured. The weight difference between
start and end weights was recorded, as the weight difference
in grams corresponds to the volume of produced gas in
milliliters. The production rate was found to be 475ml in 30
seconds, which corresponds to 57 LPH (liters per hour).
The cell was powered by a current limited (11A
limit) battery charger. The voltage and current across the
electrolyzer were measured to be 12.9 V and 11 A during the
gas collection. Thus the input power was 141.9 W.
At room temperature the Faraday efficiency would
be 0.684 LPH/A per cell. This electrolyzer should produce
about 0.684LPH/A*11A*7 = 52.6 LPH, but it produces about
57LPH. This difference is most likely explained by the gas
volume or current measurement inaccuracy.
The power efficiency was determined by dividing
the total power consumption by the amount of gas produced.
This is 141.9W / 57 LPH = ~2.49 W/LPH. The 100% efficient
electrolyzer (gas volume measured at room temperature) would
be about 1.48V/0.684LPH/A = 2.16W/LPH. Thus this electrolyzer
has about 86.7% efficiency.
However, the cell voltage was 12.9V/7 = 1.84V.
Thus the actual total efficiency is 1.48V/1.84V = ~80%.
Running internal combustion engines on
oxyhydrogen
The amount of oxyhydrogen needed to run an
internal combustion engine is spectacular. Idling a small
engine (e.g. 5hp) would require 500 -1000 LPH (liters per
hour), while idling a car engine would probably consume about
3000LPH of oxyhydrogen. Driving down the highway would
probably consume 20000-30000 LPH of oxyhydrogen. The
electrolyzer shown in this report produced approximately 57LPH
at 11A, which is not enough to idle even the smallest 4-stroke
engine (at least 300-400LPH would be required to idle a small
1hp brush cutter 4-stroke).
One liter of gasoline contains approximately
30MJ of energy, while oxyhydrogen gas would contain
approximately 7- 8kJ per liter. This means that you would need
approximately 4000 liters oxyhydrogen for each liter of
gasoline your engine currently uses, assuming the engine
efficiencies are approximately the same on oxyhydrogen than on
gasoline.
Thus if your car uses 6 liters of gasoline per
hour while driving down the highway, prepare for 24000 LPH
oxyhydrogen consumption. Assuming a super-efficient series
cell electrolyzer (2.5 W per LPH) you would need 60kW of
electrical energy to run the electrolyzer. This corresponds to
about 80hp, which is significantly more than the amount of
engine power used at highway speeds (~20hp) . Figuring in the
alternator efficiency (~50%) you would actually need 160hp on
the engine shaft to produce 24000LPH of oxyhydrogen gas.
How about a 100cc scooter powered by a 60-cell
series electrolyzer running of an 120V inverter and bridge
rectifier powered by the 12V battery? Estimated gasoline
consumption while riding at 70km/h would be about 1LPH
gasoline, which would convert to about 4000LPH of oxyhydrogen
consumption. Idling the same scooter would probably take
500-1000LPH. The 60 -cell electrolyzer would produce about 40
LPH per Amp measured at room temperature. Thus you would need
100Amps thru the 60-cell to produce 4000LPH. Because the
electrolyzer has 60 cells, you need to power it with about
120Vdc (assuming 2.0V cell voltage) from the inverter.
Assuming 100% efficient inverter, it would draw 1000 Amps from
the 12V battery to produce 120Vdc 100A. If the scooter had a
fully charged 5Ah battery it would last for 18 seconds at
1000A until it would run out. The scooters “alternator” would
produce probably about 5A maximum.
A common misconception is to think that you can
dilute oxyhydrogen gas with air and run the engine with very
small amounts of gas. Oxyhydrogen gas is in itself a perfectly
proportioned mixture of hydrogen and oxygen gasses, which
combusts perfectly leaving no hydrogen or oxygen but only
water vapor and heat. Adding any air will make it combust
imperfectly and release less energy for same volume of
gas.
An often quoted air:fuel ratio for hydrogen
combustion in air is 34:1, but this is a MASS ratio. This
means that you need 34 grams (=27.76 liters) of air for each
gram of hydrogen (=11.1 liters). Converted to VOLUME ratio
this is 2.5:1, which makes perfect sense because air contains
approximately 20% of oxygen by volume and you need 0.5 liters
of oxygen for each liter of hydrogen. Thus you need 2.5 liters
of air for each liter of hydrogen for perfect combustion
(leaving nitrogen and other atmospheric trace elements).
Assuming the engine has 100% volumetric
efficiency, a 2.0L auto engine running at 2500RPM would have
have a total air intake flow of 150000LPH. Running this engine
fully unthrottled at 2500RPM to produce the maximum power
would take about 43000LPH of hydrogen gas and 107000LPH of air
for stoichiometric operation. The 43000LPH of hydrogen
contains about 43m^3/h*2.8kWh/m^3 = ~120kW of power. Assuming
25% engine efficiency you would get about 30kW or 37hp shaft
horsepower.
Figure 14 shows the experimental setup that was
used for idling a 6.5hp 200cc 4- stroke Honda copy on
oxyhydrogen gas. The electrolyzer did not produce enough
oxyhydrogen to run the engine continuously, but the
oxyhydrogen gas was first collected in a balloon and then used
to run the engine. The 7-cell unit was used, powered by a
current limited welding transformer running at about 40A
producing approximately 200 LPH of gas. The gas was collected
for 1-2 minutes which later ran the engine for some 20
seconds. Approximately 600-800LPH of gas would have been
needed to idle the engine continuously. The engine timing was
not changed in any way. The electrolyzer gas output tube was
routed to a propane adapter bolted at the intake of the carb.
The oxyhydrogen was admitted thru a narrow (1-2mm) orifice to
the intake of the carburetor. The engine ran fully choked,
with no outside air used at all. The engine would not run
without the narrow orifice or without being fully choked.
Figure 14. 6.5hp 200cc 4-stroke running on
electrolytic gas
Implosion
There is a common misconception that when the
engine runs on oxyhydrogen it operates by imploding the
oxyhydrogen gas in the cylinders supposedly creating a vacuum
that pulls the cylinders up, thus requiring altered engine
timing.
One mole of water (~18ml) turns into 33.6 liters
of oxyhydrogen gas. Thus you get about 1860 liters of
oxyhydrogen for each liter of water, and correspondingly one
liter of oxyhydrogen turns into 1/1860 = 0.53 milliliters of
water.
But you only get a vacuum if the produced water
vapor (steam) can condense, and you only get condensation if
the combustion chamber is very cold. Steam will not condense
on the hot cylinder walls of the engine and you won’t get a
vacuum in the cylinders as a result of oxyhydrogen
combustion.
One mole of water (~18ml) will turn into 33.6
liters of oxyhydrogen at 0 deg C, but when the oxyhydrogen is
combusted it will turn into 100 deg C steam. Assuming the
steam is at 1 atm pressure, it will occupy a volume of about
30.6 liters (one mole of 100 deg C steam).
In reality the oxyhydrogen gas combusts in the
engine just as any gas (even though the flame front proceeds
quite fast), creating a rapid pressure/heat increase which
then runs the engine.
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