Bulk modulus of biodiesel (BD) described as cause of increase in BD NOx.

[NNadir]

From the upcoming issue of Energy and Fuels (Now available to online ACS journal subscribers as an ASAP version):

"The addition of biomass-derived fuels and synthetic
fuels to diesel fuel basestocks is a means of producing
a cleaner-burning diesel fuel. Blending with oxygenated
or zero-sulfur fuels can lead to reduced particulate
emissions by interfering with the soot formation process
and by decreasing the formation of sulfates. However,
in the case of biodiesel fueling (e.g., “B20”, a blend of
20 vol % biodiesel in diesel fuel), there is a welldocumented
increase of 2%-4% in NOx emissions.1
There is evidence that this increase in NOx emissions
is related to an advance in fuel injection timing. It is
well-known that advancing the injection timing can lead
to an increase in NOx emissions from direct injection
(DI) diesel engines.2
Several researchers have reported an advance in the
fuel injection timing when biodiesel is being used. Choi
et al.3 reported an advance in fuel injection timing, of
0.6 crank angle (CA) degrees, with a 40 vol % blend of
biodiesel."

From the article, it seems that an advance in the injection timing (and I am not an automotive engineer) resulting from a higher bulk modulus in biodiesel as compared to ordinary diesel occurs. This effect seems to derive from changes the speed of sound in the injector system.

If we have any diesel engineers here, I would be interested in comments.

If so, if I understand it correctly, it may be possible to reduce the NOx drawback of biodiesel by building engines with injectors specifically designed for biodiesel burning.

I don't necessarily think that biodiesel is long term viable solution to the world's energy problems, but it does represent a possible "bridging" fuel while better alternatives are developed. A reduction in the primary hazard associated with biodiesel, increased NOx would therefore be a welcome development.