Emissions of biodiesel engines

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 engine–vehicle 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

last modification  07.06.02   by