San Diego - Regulatory and lawsuit pushes to ban clean-diesel technology look arbitrary and biased in the light of growing evidence that particulate trap-equipped diesels running on ultra-low-sulfur diesel (ULSD) fuel produce even less cancer threat than compressed natural gas (CNG) emissions.
Government-sponsored emissions testing research on PM filter-equipped New York Metro Transit Authority (MTA) buses running on ULSD shows that clean- diesels produce none of the cancer-causing carbonyl emissions, unlike transit buses running on CNG. The new finding confirms the results of a new Swedish study comparing PM trap-equipped clean-diesels to CNG and alcohol fuels (see Diesel Fuel News 7/17/2000).
The carbonyls include aldehydes such as formaldehyde, acetaldehyde, acrolein and propionaldehyde, all considered "very toxic" and cited on EPA's "hazardous air pollutant" (HAP) list, notes Sougato Chatterjee, Johnson-Matthey senior applications scientist. Some of these carbonyls are also part of EPA's recently published list of "air toxics" that pose threats to public health in urban areas (see Diesel Fuel News 8/14/2000). Chatterjee showed the new emissions test results at the Diesel Engine Emissions Reduction workshop here, sponsored by U.S. Department of Energy.
MTA, New York State Department of Environmental Conservation, Johnson-Matthey (JM), Equilon, Corning, Environment Canada, and RAD Energy are cooperating in the New York clean-diesel test program, including a fleet demonstration with 25 buses using JM's "CRT" soot filter. Environment Canada laboratories are performing the emissions testing with a chassis dyno, using both the Central Business District (CDB) and the much more aggressive New York City (NYC) bus test cycles.
Results of these chassis dyno emissions tests were compared to recent CNG bus emissions test results from Los Angeles MTA (at CARB/MTA facility), New York MTA (at Environment Canada) and the Northeast Advanced Vehicle Consortium (see Diesel Fuel News 3/6/2000) by West Virginia University's renowned portable chassis dyno. All the CNG buses were equipped with oxidation catalysts.
As usual, CNG technology showed very wide swings in nitrogen oxides (NOx) emissions from one bus to another. Some NOx emissions levels with CNG were much higher than clean-diesel, although the "average" CNG bus produced slightly lower NOx than today's PM filter-equipped clean-diesels. However, CNG carbonyl emissions were about 3 grams per mile, compared to zero for the CRT-equipped clean-diesel buses, Chatterjee showed.
Particulate matter (PM) emissions were about the same for both CNG and clean- diesel - slightly lower with CNG on CBD cycle, but slightly worse than clean- diesel on the more aggressive New York bus cycle.
Hydrocarbon (HC) and toxic carbon monoxide (CO) emissions are much lower with CRT-equipped clean-diesel compared to CNG, the tests show.
- Jack Peckham
The commonly used cold filter plug point (CFPP) test over-predicts the efficacy of cold-flow improver additives on biodiesel blend, according to a Technical Research Centre of Finland study.
The study, presented in a paper to Society of Automotive Engineers fuels & lubes conference (SAE 2000-01-2009), found that a 20% blend of rape methyl ester (RME) biodiesel degraded the cold-startability of diesel by 4oC. Adding a cold-flow improver additive supposedly depressed the CFPP to -21oC, but in fact the real starting temperature of the additized biodiesel was only -15oC, the study showed.
"Normal laboratory analyses overestimates the cold performance of RME blend," the study found. "The RME blend had a strong response on CFPP with the additive," but "again the laboratory tests overestimated the cold performance of RME blend." Likewise, the standard cetane test engine grossly over-estimated cetane improver addition to biodiesel blend, by some 12-15 cetane units, the study found.
Meanwhile, a 15% ethanol-diesel blend in the tests produced the highest hydrocarbon and carbon monoxide emissions in the tests on a heavy-duty Volvo bus engine, but the lowest nitrogen oxides (NOx) and particulate matter compared to ordinary European diesel fuel. Adding RME to the ethanol blend boosted cetane and helped reduce HC emissions.
Ethanol emulsion without RME additive failed to deliver proper performance in either a Volvo bus engine or the cetane engine.
On a light-duty Audi TDI car, the ethanol fuels produced "extremely high HC emissions" compared to ordinary diesel fuels, but didn't reduce NOx as in the heavy-duty tests