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NREL B20 Study Shows No Increase in NOx Emissions

Comparison of NOx emissions for conventional diesel and B20 for each vehicle tested and each cycle. Click to enlarge.

A recent study by the US Department of Energy’s National Renewable Energy Laboratory (NREL) concludes that vehicles using a B20 biodiesel blend (20% biodiesel and 80% petroleum diesel) do not produce an increase in nitrogen oxide (NOx) emissions. These findings counter those of an earlier Environmental Protection Agency 2002 report showing a two-percent increase in NOx emissions for B20.

For the study, NREL tested entire vehicles on a heavy-duty chassis dynamometer at its Renewable Fuels and Lubricants Research Laboratory (ReFUEL). The vehicles included three transit buses, two school buses, two Class 8 trucks, and one motor coach.

Using the chassis dynamometer, NREL researchers simulated both urban and highway driving for each of these vehicles. In addition, NREL reviewed previously published results for engine and chassis testing of B20.

This is a major finding because the perceived small increase was leading some state regulatory agencies to consider banning B20 biodiesel. Our study helps remove a significant barrier to the expansion of biodiesel markets.

Our study shows that the NOx impact of B20 varies with engine design, such that some engines show a small increase while others show a small decrease. The EPA’s 2002 review was based on a data set made up primarily of data from one engine model that produces a small NOx increase. EPA uses these data to draw a general conclusion for on-highway engines that B20 causes a 2% increase in NOx. The chassis dynamometer testing along with careful review of previously published data suggest that their conclusion is not correct, and that on average B20 has no effect on NOx.

—Robert McCormick, NREL Principal Engineer for nonpetroleum based fuels research



Spokane Walt

Yes, and with some engine tuning for BioDiesel the NOx could be further reduced - In other words, if an assumption can be made that all Diesel sold is at least 3% Biodiesel, then some tuning could be to factor that in.


Engine mapping wil be important, to get the most out of biodiesel, and other potentially cleaner fuels. Just because the engine will run, unaltered, with the fuel does not mean all is right. With biodiesel, they can favor NOX a bit due to PM matter from methyl esters are smaller, less abundant, and easier to catalyse into CO2 in particulate filters.
___There is also the issue of FAME (using CH4O), FAEE (with C2H6O), and other esters (propanol, butanol, etc). Mathanol is cheaper, but predominantly derived from fossil energy. This can be changed by using biomass derived Syngas to make CH4O. Ethanol come from various sources, and can also benefit from Syngased biomass. The same is also true for other alcohols.
___The point may be moot if renewables based BTL fuels take hold.

kent beuchert

I consider a biodiesel vehicle that isn't a tractor pulling a trailor a hopelessly outdated technology. Electric cars with batteries is the obvious future
trend. Use biodiesel in powerplants as a stopgap until
clean energy is universally provided. An internal combustion engine is hopelessly energy inefficient and
has no place in the coming energy economy.

P Schager

If all you're doing is tinkering with the fuel and adding a little biodiesel as an additive, why not while you're at it put in other additives that will cut the NOX? Water emulsion is one that should work, and there are others.

Biodiesel particulates (cooking fumes) are in any case far less unhealthy than those of petrodiesel, so even if you did see a small rise in NOX with B20 your city would be better off, and you could reduce air toxics cheaply enough you come out ahead if you pay somebody else to cut NOX. B100, even better--especially for old diesels. Oxygenated biodiesel, more of the same story.

The best next-generation car would be a modern diesel in a PIHEV, with NOX aftertreatment and a CRT, powered by biodiesel and/or BTL and solar panels on a roof for the juice. CO2 neutral, no sulphur, no blood and will keep us breathing until we get that suitable all-electric car. And bridge the humungous industrial/political inertia.


Electric cars? And where do you think we are going to make all that electricity from. About 80% of the US's electricity it made from burning coal. And besides who cares about emissions? It's about getting off our dependence on foreign oil and saving our economy. Then we can worry about emissions.

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