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Sugar water as a fuel?

Sugar water as a fuel? - Chemistry Forum

Sugar water as a fuel? - Chemistry Forum. Discuss chemical reactions, chemistry.


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  #1  
Old 07-30-2003, 08:47 PM
Roland Paterson-Jones
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Default Sugar water as a fuel?



Hi all

It's a well known urban myth that you can destroy an engine by dumping sugar
in the fuel tank. In fact, sugar (sucrose) doesn't dissolve in gasoline, and
the worst you can do is clog up your fuel filter.

Now, to turn the myth on its head, why are sugars (sucrose, glucose,
fructose) so useless as fuels in internal combustion engines? They are
soluble in both water and ethanol (sherry, anyone?), so are easily delivered
to the combustion chamber.

I guess this is a chemistry question, and my gut feel is that they 'char'
too easily. In other words, the combustion reaction is too prone to
producing raw carbon, without oxidising the carbon to CO2.

On the other hand, perhaps the problem is pragmatic, in that that sugar
solutions tend to crystalise and adhere to the fuel supply. You'd get toffee
as a daily bi-product of your engine, in other words.

I'm interested in any further wisdom (and wise-cracks) in this vein.

Thanks
Roland

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Roland and Lisa Paterson-Jones
Forest Lodge, Stirrup Lane, Hout Bay
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mobile: +27 72 386 8045
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  #2  
Old 07-30-2003, 11:07 PM
Roland Paterson-Jones
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Default Sugar water as a fuel?

"Steve Turner" <[Only registered users see links. ].net> wrote in message
news:[Only registered users see links. ]...
delivered

OK, C12H22O11, saccharose, has enthalpy of formation of 5166.2 kJ/mol. By
comparison, C12H26, n-Dodecane has enthalpy of 7518.8 kJ/mol. Of course,
C12H26 has molar mass of 170kg/kmol, whereas C12H22O11 has molar mass of
342kg/mol.

Add to that, the solvent, water, at 50% per weight, and saccarose/water
solution has 1/4 the energy/mass of dodecane.

Latent heat of vaporization of water is 2257kJ/kg. Molar mass of water is 18
kg/kmol. Latent heat of vaporization is 2257kJ/kg * 18kg/kmol = 40.6kJ/mol.

Solution of 50% by weight is 1 mol C12H22O11 to 342/18 mol H2O = 19 mol H2O.

So, we waste 40.6kJ/mol * 19 mol = 771 kJ in vapourising the H2O solvent,
while burning 5166.2 kJ of C12H22O11.

Is my arithmetic correct?

I guess a 50% by weight solution of sucrose is a little viscous to use as a
fuel. However, even a 25% by weight solution looks good according to the
above figures.

Comments?

Roland
--
Roland and Lisa Paterson-Jones
Forest Lodge, Stirrup Lane, Hout Bay
[Only registered users see links. ]
mobile: +27 72 386 8045
e-mail: [Only registered users see links. ]



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  #3  
Old 07-30-2003, 11:09 PM
Bruce Hamilton
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Default Sugar water as a fuel?

On Wed, 30 Jul 2003 22:47:07 +0200, "Roland Paterson-Jones"
<[Only registered users see links. ]> wrote:


In the old days ( before emissions were a problem ), many vehicle fuel
tanks freely vented to the air, so some water was always slopping
around the bottom. Adding sugar dissolved into the undissolved water
and then formed an immiscible layer on the filter. Modern fuel systems
aren't freely venting, and often have oxygenated fuels that scavenge
the water, so it's no longer a problem.


Water is useless as a fuel, but it can be used to improve combustion
conditions once there is sufficent fuel to overcomne the quenching
effects. The basic requirement of a fuel for modern SI engine is that
it vaporises ( only gaseous fuels combust ). Sugars don't.

Yes, diesels do work with powered and emulsified fuels ,and you could
grind sugar into a fine dust so it would combust or explode, but there
are a whole heap of other hadling and combustion performance issues.
Dissolving the sugar into a solvent, ( 200g into 100ml H2O or 0.5g
into 100ml EtOH at 20C ) isn't viable. You would have to aerosol the
syrup in the case of water, and the quenching effect of the water
would be huge, and there is no benefit in adding 0.5% of sugar to
ethanol.

Engine performance on any sugar will be inferior to a clean
hydrocarbon liquid ( which is just C and H doesn't have the O from
sugars' CHO ), so why bother?.


No - they just aren't worth the hassle, either economically or
performance wise. They don't vaporise and form a flammable mixture
that can burn easily and consistently. Brazil chose to convert
sugar/carbohydrate materials to ethanol, which at least can burn in
engines with minimal modfications.


No there are diesels that run on pulverised coal, and finely ground
sugar, properly aspirated into a CI engine would work, but it's not
worth the hassle. Liquid hydrocarbons are a wonderful transport fuel,
with the hydrogen forming water and the carbon forming CO2, without
any additional oxygen being carried around unnessarily, given that
it's conveniently available from the air.

Bruce Hamilton

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  #4  
Old 07-31-2003, 12:49 AM
Roland Paterson-Jones
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Default Sugar water as a fuel?

"Bruce Hamilton" <[Only registered users see links. ].nz> wrote in message
news:[Only registered users see links. ].nz...


I struggle to believe your explanation, since water 'slopping around the
bottom' would cause immediate failure to start. Either the fuel line is
above the water 'slopping around the bottom' or it isn't.



Hydrocarbon fuels in ICE engines are supplied as a mist of small droplets.
These droplets combust in the cylinder outside-in (heat of combustion
evaporates the fuel, leading to further combustion). Sure, some of the fuel
is vaporised by the time it ignites, but almost all of it is in the form of
fine droplets.

Sugars don't vaporise (they are solids), but they can be carried to the
combustion chamber in the same droplet form (in solution) as the standard
hydrocarbon fuels.


I have done the quenching calculations in another post, here is the summary

"So, we waste 40.6kJ/mol * 19 mol = 771 kJ in vapourising the H2O solvent,
while burning 5166.2 kJ of C12H22O11"


Well, I might have access to cheap sugar, for example. I have to agree that
performance is likely to vastly inferior to that of the standard fuel.


In fact ethanol allows higher compression ratio's than gasoline.

toffee

Yep, you can't beat hydrocarbons, unless you don't have them. There's no
need to grind sugar, brownian motion in solution will suffice.

I am more interested in any real experience with sugar solution combustion.

Thanks for your help
Roland



--
Roland and Lisa Paterson-Jones
Forest Lodge, Stirrup Lane, Hout Bay
[Only registered users see links. ]
mobile: +27 72 386 8045
e-mail: [Only registered users see links. ]




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  #5  
Old 07-31-2003, 01:41 AM
Roland Paterson-Jones
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Default Sugar water as a fuel?

Dear Ian

Enthalpy of formation is a closed system. In other words, _formation_ is
simply a by-word, indicating that some of us know what we mean. Similarly,
the zero point is adopted according to custom. You might be Ian, and you
might well be Gay, but you should understand that energy of formation is
equal to energy released by 'combustion', or, in other words, energy
released when the chemical is rendered to the zero point, in this case CO2
and H2O.

Thanks for your valuable contribution to my understanding.

I am 6'4 and black. I have a good build. Would you like to see me privately?

Roland

--
Roland and Lisa Paterson-Jones
Forest Lodge, Stirrup Lane, Hout Bay
[Only registered users see links. ]
mobile: +27 72 386 8045
e-mail: [Only registered users see links. ]

"Ian Gay" <[Only registered users see links. ]> wrote in message news:bg9qhp$dbr$[Only registered users see links. ].ca...


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  #6  
Old 07-31-2003, 02:27 AM
Bob
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Default Sugar water as a fuel?

On Thu, 31 Jul 2003 04:11:04 +0200, "Roland Paterson-Jones"
<[Only registered users see links. ]> wrote:


Thanks for explaining what you mean by heat of formation, as that
seems to be at the root of misunderstanding.

But that is certainly not the standard meaning of heat of formation
taught in US, or found in US reference books. I believe that European
usage is the same, but someone else will need to verify that. The heat
of formation is a hypothetical value, based on formation from the
elements (in their standard states).

Heat of combustion would be the heat of formation of one mole of the
sugar minus the heats of formation of the appropriate moles of CO2 and
H2O. No need to consider the O2, because that is its standard state.
(Hm, if you have CO2 and H2O at zero, then you cannot also have O2 at
zero??? Fishy.)

bob
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  #7  
Old 07-31-2003, 02:47 AM
Roland Paterson-Jones
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Default Sugar water as a fuel?

"Joćo Antonio" <[Only registered users see links. ].br> wrote in message
news:bg9vjl$8ie$[Only registered users see links. ].ntu.edu.tw...


Joćo, my point is that enthalpy of formation and enthalpy of combustion are
one and the same.

Look it up in your handy chemical text. Do you find separate entries for
enthalpy of formation and enthalpy of combustion? No! it's one and the same.

Listen, I am a 6'4 black man, and I can handle myself. I like hispanics, but
I think Ian is my man. He was short (maybe tiny?) and to the point.

Roland

--
Roland and Lisa Paterson-Jones
Forest Lodge, Stirrup Lane, Hout Bay
[Only registered users see links. ]
mobile: +27 72 386 8045
e-mail: [Only registered users see links. ]

Similarly,
CO2


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  #8  
Old 07-31-2003, 03:04 AM
Roland Paterson-Jones
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Default Sugar water as a fuel?

"Bob" <xyzbbruner@uclink4.berkeley.edu> wrote in message
newshvgivsis3t2k8ln7c5bhetdq1jg270ktq@4ax.com...

Yep, such is the state of our current thermodynamic texts. All of H2O, CO2
and O2 are considered to hover at 0 enthalpy of formation. I am taking this
from standard tables.

Of course, if you can find a way of breaking the standard tables, you have
found a way to produce unlimited energy.

No-one has done so up til now.

roland

--
Roland and Lisa Paterson-Jones
Forest Lodge, Stirrup Lane, Hout Bay
[Only registered users see links. ]
mobile: +27 72 386 8045
e-mail: [Only registered users see links. ]



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  #9  
Old 07-31-2003, 04:10 AM
G. R. L. Cowan
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Default Sugar water as a fuel?



Roland Paterson-Jones wrote:

Yes.


No.


--- Graham Cowan
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how cars gain nuclear cachet
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  #10  
Old 07-31-2003, 06:32 AM
Bruce Hamilton
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Default Sugar water as a fuel?

On Thu, 31 Jul 2003 02:49:19 +0200, "Roland Paterson-Jones"
<[Only registered users see links. ]> wrote:


If you look at the fuel tank design specification for a 1920s - 1960s
vehicle, they have a small shallow well, usually with a capacity of
about 100 - 400ml, and the early ones also had a drain plug, and the
fuel line inlet sat about 1/2 - 3/4 the way up - so vehicles could use
almost all of the fuel. That well was intended to trap water that
either condensed or arrived entrained in the fuel, and water slopped
around the bottom of that well. Added sugar would eventually end up
there as well.


Every CNG engine I've seen used compressed gas. I repeat, only
gaseous hydrocarbon fuels combust.


You are obviously authoritative, so I'm sure you'll have heaps of
references to support that statement. Please provide some, as it
conflicts with the ones I have, eg SAE 961122 " Vapor/liquid
visualization with laser-induced exciplex fluorescence in an SI-engine
for different fuel injection timings". Please be specific with your
references.

There is plenty of evidence that great care has to be taken with GDI
to ensure that the fuel is a vapour and well mixed before the flame
front arrives. Otherwise HC emissions increase dramatically, and any
search of the SAE database will confirm that undesirable link.


A liquid spray is quite different to a solid spray, on a macro scale
consider rain and hail. If you have data on a SI engine that uses a
significant amount of solid suspensed in water as a fuel, I'd be
interested in the reference. CI engines are much more tolerant, and
pulverised and emulsion fuels have been used, usually on the slow
speed types.


Ok. let's look at this quickly using a 25:75 sugar water mix. This
could be wrong, as I'm in a hurry, and can't check the data.
Now even a 25% sugar solution is a viscous syrup, and there isn't much
chance of getting it to aerosol in any sensible way.

[Only registered users see links. ]
Heat of combustion of sucrose is 5639.7 kJ/mole ( 16.5 MJ/kg )
25/342.3 x 5639.7 = 412 kJ

Heat of vaporisation of water is 40.7 KJ/mole
Specific heat of water = 4.18 J/g/c ( assume 20 to 100C )
Specific heat of steam = 2.02 J/g/C ( assume 100 to 600C )
75/18 x 40.7 = 170 kJ
75 x 4.18 x 80 = 25 kJ
75 x 2.02 x 500 = 76 kJ
Total = 271 kJ

Now a 100g of gasoline ( ~42 MJ/kg ) produces about 4200 kJ
A 100g of your mix will produce 141 kJ.

Congratulations.


Depends on the gasoline.

Bruce Hamilton
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