PWM
Veteran Member
- Joined
- May 10, 2000
- Location
- Western Siberia (Finland)
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
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