Harmon Seaver wrote:
> I think you don't understand what octance (cetane) ratings are all about.
> If
> anything, with a higher octane (or cetane, as the case may be) you would
> benefit
> from *advancing* the timing, not retarding it. At any rate, where did you get
> this idea of changing the timing for biodiesel anyway? There's absolutely no
> basis for it that I'm aware of, in any of the documentation.
CETANE NUMBERS
EUROPE: 43 - 57, average 50
U.S. lower, minimum 40, average 43
Higher cetane correlates with:
improved combustion
improved cold starting
reduced noise, white smoke, HC, CO and particulate
emissions particularly during early warm-up phase
"MOTOR VEHICLE FUELS"
www.carleton.ca/~dkarman/82571/FUELS2.ppt
One approach often used to mitigate the NOx increase associated with biodiesel
is to change the timing of the engine. Retarding the timing of these engines
tends to reduce NOx emissions at the expense of increasing PM10.
"Urban Bus Operation"
http://www.worldenergy.net/articles/supportRes/documents/lifecycle_ch6.pdf
CONCLUSIONS
Fueling with biodiesel/diesel fuel blends effectively reduced particulate
matter,
unburned hydrocarbons, and carbon monoxide while increasing oxides of nitrogen
emissions.
The optimum blend of biodiesel and diesel fuel, based on the trade-off of PM
decrease and
NOx increase, was a 20/80 biodiesel/diesel fuel blend.
Increased NOx emissions can be reduced by retarding engine timing while
subsequently
maintaining emission reductions associated with fueling a diesel engine with a
20/80
biodiesel/diesel fuel blend. The retarded timing lengthened the ignition delay
time.
This reduced the peak pressure and temperature that enhance the formation of
NOx emissions.
"FUELING DIESEL ENGINES WITH BLENDS OF
METHYL ESTER SOYBEAN OIL AND DIESEL FUEL "
http://www.missouri.edu/~pavt0689/Fueling_Diesel_Engines_with_Blends_of_Methyl_Ester_Soybean_Oil.pdf
Emissions of NOX
from biodiesel vehicles can be reduced substantially by adjusting the timing
of injection.
The Austrian study quoted above shows that, in buses, NOX emissions were
reduced by 23%
relative to fossil diesel by advancing injection timing.
http://www.biodiesel.co.uk/press_release/submission_for_biofuels_2.htm
Speed of sound and bulk modulus appear to cause ignition timing to advance
by an average of one degree. This tendency contributes to some but not all of
the
increase in NOx emissions commonly seen in biodiesel engine stand emission
tests.
This information could also be used to support efforts to retard engine
timing,
although research on timing retardation with biodiesel and biodiesel blends
show
other emissions increasing when this occurs. A B100 engineövehicle system may
eliminate or reduce the amount of NOx produced by biodiesel fuels, although a
significant amount of engine mapping and research on fuel spray patterns,
droplet size,
droplet density, and other systems would be needed to accomplish this. Some of
this
research is underway in other projects.
"Measurement of Biodiesel Speed of Sound and Its Impact on Ignition Timing"
http://bioenergy.ornl.gov/99summaries/biodiesel.html
Looking at Flash Point of Petro-Diesel & Biodiesel
60-80 C, 100-170 C
"Biodiesel - Clean Green Diesel Fuel"
2 page PDF > http://www.nrel.gov/docs/fy01osti/30882.pdf
I would think advancing timing would increase biodiesel combustion.
Searching Google brought forth far to many reports.
`
Biofuel at Journey to Forever:
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