About Fumigation

[PWM]

Hi !

Noe I have red a bunch of articles about the fumigation and bi-fuelling..

I writed a short note about the issue:

"

_Fumigation_

The effects of fumigation in diesel engine is caused by several phenomenas:

1. Evaporation of the fumigated liquid.

In the fumigation process a carbohydrate liquid is sprayed to the intake manifold
in a from of fine mist. (The mist must be very fine in case of carbohydrate having
a lower boiling point than the intake air temperature. This is to be able evaporate
all of the liquid to gaseous state.) The evaporation of the liquid absorbs energy
from the intake air-flow thus lowering the temperature. The lower temperature
increases the density of air. Higher density air leads to better filling and to
higher mean effective pressure.

2. Slow oxidation

The air-carbohydrate -mixture gets hotter and high-pressurized by the compression
cycle. The temperature and pressure begins to partially oxidize longer carbohydrate
chains. The oxidation releases small amount of heat. The results of this process is
short partially oxided carbohydratels, like peroxides and aldehydes. (CO, CO2 or H2O
does not form.)

3. Cracking

Cracking is pyrolysis or thermal decomposition of the carbohydrate. Cracking happens
in parallel with the slow oxidation. Here longer carbohydrate chains are braking down
to form shorter chains. The breakage of chemical bonds absorbs energy (, thus cooling
the mixture).

4. Flame catalyzation

Cracking before the ignition is essential to form small particles needed to start the
flame. Small carbon particles act as nuclei to initiate combustion. When fumigation is
used the total air-volume is filled with such particles before the main fuel is sprayed.
This phenomena decreases the ignition lag.

5. Air-efficiency

Normally diesel process uses only small fraction of the oxygen available. Fumigation
causes the air-volume to be filled with lean (uncombustable) fuel mixture. When the
main fuel is sprayed to this lean mixture the result mixture is able to utilize almost
all oxygen available. Because the mixing of the main fuel to the air-mixture is slow
knocking does not happen.

Phenomanenas 2. & 3. can cause negative work on compression and positive on expansion
cycles. This has been demonstarted by running an engine without flame or combustion
by only fumigation. (The energy to run the engine is taken from the cracking in
compression and from slow oxidation in expansion - The exhaust is smaller partially
oxidized carbohydrate chains in form of warm steam..)

And some numbers from the measurements :
(Approximate - from curves ..)

Constant power:
Exhaust temp. 770 680 650 630 630 630 F
Smoke density 60 35 20 16 15 15 %
BSFC .69 .66 .63 .64 .65 .67 LB/HPhr
MaxPressRise 60 45 41 40 40 40 psi/deg.
MaxPressure 860 880 910 920 930 930 psi
Ign.delay 8 7 6 4 3 1 deg.
Fumigation 0 5 10 15 20 25 %m of tot.fuel

Constant smoke density (60%) :
Exhaust temp. 730 740 750 760 670 F
BMEP 56 62 65 66 68 Psi
BSFC .69 .67 .66 .67 .68 LB/HPhr
MaxPressRise 60 55 50 45 40 psi/deg.
MaxPressure 860 900 920 930 928 psi
Ign.delay 6 5 3 2 0 deg.
Fumigation 0 5 10 15 20 %m of tot.fuel

- In a nutshell 20% fumigation of the total fuel mass
gives the maximum power, lowest noise (smallest
pressure rise speed), lowest ignition delay.

One paper states that is possible to get 400 psi
mean brake effective pressure (BMEP) with
super charged diesel. This was archieved with
lowering the compression ratio to ~8 and using
37psi boost pressure with 104F temperature.
Because of the low compression ratio the
peak pressure were only 1600 psi. The motor
was modified from commercial design by
mashining the piston. (TDI pistons Z-type
piston could be easily modified to high-
turbulence type by machining it to be
half dome like. This would drop the compression
ratio laso ..)

As a conclusion it seems theoretically possible
to archieve 5-6 times the normal power with
TDI engine by lowering the compression ratio to
8-10 and taking charge pressure to 35psi with
efficien aftercooler together with intake manifold
fumigation and perhaps water sprays (to cool the
engine).

To be able to benefit from the evaporation the
fumigation and water spraying should happen after
the aftercooler !


"

.. hope this clarifies something to someone ;-)


BTW. Who wants to be the first to build such engine !?!
- I could have some ideas !! ;-)

Greetings,
PWM

 

[valois]

Readers digest condensed version..... It makes car go faster, quicker, cleaner, economically.

 

[SkyPup]

change the word "carbohydrate" to "petrochemical", we are talking engine fuels here not about making bagels!")

 

[Drivbiwire]

Please pass the Philly...

 

[Ron Schroeder]

Good info PWM,

Where is it from? The last technical info that I read was in the OSU engineering library almost 20 years ago.

Ron

 

[mickey]

"Carbohydrate"??? Starchy fuel? "Hydrocarbon" is the word you're looking for.

I can just picture little sugar "stalagtites" hanging from the tailpipe.

-mickey

p.s. Visions of the "Mr. Fusion home-energy reactor" from Back To The Future! Drop your kitchen waste into the engine, and PRESTO! Instant fuel.

 

[PWM]

Hi all !!

Sorry but my english is not the best ;-)

An some additional notes about the measurements ..
Those was made in relatively slow RPMs - all under 2800RPM !
And the ignition lag of the main fuel is masked by
the fumigated fuel - So the actual ignition
delay of the main fuel is not so small in higher RPMs !!
.. So normal advance should be okay anyway ;-)

 

[valois]

PWM Your command of English as a secondary language is very good, and the information you have posted is informative and well recieved. Tell us more, where did you collect it? I have noted first hand the effects you describe, and am interested in your references. Basically, fumigation would be even more effective on an older engine,(less compression) increasing past the magic 20% and bleeding the boost sense to take advantage of it. I will be installing a boost guage this weekend and increasing my boost from 13 to 18psi continous, I'll report on wether the system will be able to take an increase in fumigation.

 

[SkyPup]

Yes, thanks for the information, I apologize for sniping on you about the English translation, I had no idea you were from another country.
We would be interested in sharing your experiences with propane fumigation in your diesel here though, no matter where in the world you are.

Welcome!

 

[Powder Hound]

This is really good stuff, PWM!

Valois - any eta on when we will get an economy valuation from you? It would seem that with the relatively high BSFC numbers, the theory on better combustion of the diesel must be what makes things work. I'm waiting to hear.

------------------
Always interested in steep & deep.
Ski resorts closed! Break out the cameras and fly rod ...

 

[valois]

I should be sticking close to home this week and will be able to put some more miles on it. So far I have a grand total of 150 miles since installing the system. Most of that has been at WOT.

So far I've used 1/4 tank of diesel and 3/8 of the tank of propane.

 

[PWM]

The info is from SAE -series called Advances in Motor Technology : Using different fuels in high-speed diesel engines ..
(Or something like that .. I doesn't just now
have the book in hand
- I'll post the correct reference later ;-)
All info about fumigation is quite old..
Perhaps there is nothing new in that field anymore !

 

[valois]

PWM add a 40% mixture of Butane to the Propane, reduce the fumigation rate slightly and recalculate!

 

[PWM]

The exact reference:

Society of Automobile Engineers - Progress in Technology vol. 11 :
Burning a Wide Range of Fuels in Diesel Engines
p.213 M.Alperstein, W. B. Swim, P. H. Schweitzer :
"Fumigation Kills Smoke -- Improves Diesel Performance"

.. there's also another intresting article:
p.129 W. P. Mansfield and W. S. May :
"Diesel Combustion at High MEP with Low Compression Ratio"

And to Valois :

I don't think that the butane/propane mixture makes much difference ..
and the limitation to the fumigation rate is to keep the mixture under the combustion limit. (So that preignition does not happen in lean mixture when in compression cycle..
Fumigation limit should be directly proportional to the mass flow of air.)

And again note from Coluccis dyno-figures ;-)
The torque dropped from about 2200 ..
If you could get the same torgue at 4400
- then there would be 2x power ;-) (or 260 hp !!)

So there's plenty of potential (even without fumigation) !!

 

[valois]

PWM has expressed some interest along with others on alternate methods of metering fumigation. The other thread on Propane injection was getting too long and was closed. Please post your ideas here.

 

[Ron Schroeder]

PWM,

Yes, I think that the fumigation LIMIT should be proportional to the MAF to prevent a rich mixture. But I think that the mixture below the limit should be proportional to the fuel flow. If it was metered by MAF then medium rpm, light load would fumigate too much propane possibly causing a runaway condition. My experimentation was with a NA diesel but I think that controlling fumigation based on air volume would cause drivability problems which may be even worse in a turbo diesel. The optimum Diesel/Propane ratio seemed to be not very critical except at idle where it could easily cause overspeed if too much propane was used. I got around that by using a switch on the pedal so no propane was injected when my foot was off the pedal. I was primarily trying to improve economy since I did not have as much excess air as a turbo but the extra power was quite noticable. The fumed NA Isuzu had almost the power of the turbo Isuzu that my friend had.

Ron