12/15/2004 Renewable Fuel News - Biodiesel used in existing dieselvehicles not fitted with aftertreatment devices results in "similar"carbon monoxide (CO) and nitrogen oxides (NOx) emissions levels whencompared to conventional diesel fuel, but particulate matter (PM)emissions "are clearly raised" when making the same comparison. That'saccording to results of a biodiesel test carried out by Japan's NationalTraffic Safety and Environment Laboratory, which was released by theMinistry of Environment.

While CO and NOx emissions levels are "similar" when comparing biodieselwith conventional diesel, the study found that emissions of thosepollutants can "in some cases" be slightly elevated in the case ofbiodiesel. "PM levels are clearly raised, with the reason being that fattyacid methyl ester in the biodiesel fuel is emitted unburned as [solubleorganic fraction>," the report said.

"For this reason, if biodiesel fuel is to be used in diesel vehicles, itis considered necessary to fit their exhaust systems with aftertreatmentdevices such as a catalyst unit with high oxidation performance(strong-oxidation catalyst) or a DPF [diesel particulate filter> unit withoxidation catalyst, in order to counter PM, CO and other emissions," thereport added.

When biodiesel is used in vehicles fitted with aftertreatment devices,exhaust emissions of soluble organic fraction is reduced, as is PM,according to the report.

Based on tests of biodiesel blended with 10-ppm sulfur diesel fuel inproportions ranging from 0% to 100%, the study also found:

* "There was a tendency for the level of CO in the engine exhaust gas toincrease with higher biodiesel fuel blend ratios," which is likely theresult of biodiesel fuel being more viscous than diesel fuel, "whichresults in localized oxygen deficiency when spray auto-ignites andcombusts." Therefore, "it is thought that this effect more than overridesthe effect of biodiesel fuel being an oxygen-containing fuel."

* "No clear cause-and-effect ratio could be identified between thebiodiesel fuel blend ratio and the amount of HC [hydrocarbons> in theexhaust gas from the engine."

* "It was found that there was a tendency for NOx emissions levels toincrease with the rise in biodiesel fuel blend ratio, but at the same timeno clear relationship was found between NOx and biodiesel blend ratio."

* "In cases where diesel vehicles use catalysts with weak oxidationperformance to keep down sulfates, it was found that catalyst reactionsactually increase CO levels. However, it was found that since HCconstituents are easier to break down that CO, these are reduced to acertain extent even if the catalyst has weak oxidation performance."

* "A tendency for fuel economy to drop a little when biodiesel fuel blendratio is increased was observed. This is thought to be an issue rooted inthe calorific value of the fuel itself, so further investigation isrequired..."

* "[B>iodiesel fuel did not demonstrate much inferiority to diesel fuel interms of steady-state torque characteristics, but in transient situationssuch as under rapid acceleration, a small drop in acceleration performancewas observed as biodiesel fuel blend ratio was increased."

Overall, biomass fuels are "an effective approach in terms of policy forpreventing global warming," the report concluded. "However, in usingbiodiesel fuel, it is desirable to give proper consideration to theinfluence on exhaust gas... and to take the action required," it said."With reference to the findings of this survey, there is great potentialfor promoting widespread use of biodiesel fuel through developing specialvehicles designed from the start to use biodiesel fuel in the optimummanner at the same time as employing atmospheric pollutioncountermeasures."

--Jeremy Glunt