DPF-equipped diesel cars beat direct-injection gasoline on PM number, mass emissions

Diesel Fuel News, June 23, 2003

In tests with both 10-ppm sulfur diesel and gasoline fuels, a study (SAE 2003-01-1889, 1890) co-authored by Swiss federal research lab (EMPA) and Europe's automaker association (ACEA) shows that particle-filterequipped clean-diesel cars produce fewer mass and number emissions of particulate matter (PM) than direct-injection gasoline.

The DPF cars and port-fuel-injected gasoline cars had PM emissions so low that they're virtually identical to background (ambient) levels, the study shows. PM emissions during DPF regenerations (mostly volatile nano-PM in the range of 20 manometers) are "negligible" over the duty cycle, the study shows. Most of the PM mass emitted by gasoline vehicles and diesels not fitted with DPFs is non-soluble, rather than soluble organic fraction, the study found. Number size distribution for diesel PM emission is around 70 nanometers versus about 50 nm for gasoline vehicles. PM emissions from DPFequipped car and port fuel-injected car were so minimal that it wasn't possible to analyze composition of the particle matter. Separate tests with higher-sulfur (200-ppm sulfur) fuel showed a clear increase in PM emissions from both diesel and gasoline vehicles, the study showed. "Drastic differences were observed concerning the nucleation-mode for the test with high-sulfur fuel," the researchers found. Test repeatability was much better (over a week) with the ultralow sulfur fuels. "The results of the study suggest that the sulfur in the fuel only has an effect on the non-solid fraction of the particle emissions," the authors concluded.