In order to investigate the effect of sulfur and distillation properties on exhaust emissions, emission tests were carried out using a California Low Emission Vehicle (LEV) in accordance with the 1975 Federal Test Procedure ('75 FTP). To study the fuel effect on the exhaust emissions from different systems, these test results were compared with the results obtained from our previous studies using a 92MY vehicle for California Tier 1 standards and a 94MY vehicle for California TLEV standards. (1)(2)
First, the sulfur effect on three regulated exhaust emissions (HC, CO and NOx) was studied. As fuel sulfur was changed from 30 to 300 ppm, the exhaust emissions from the LEV increased about 20% in NMHC, 17% in CO and 46% in NOx. To investigate the recovery of the sulfur effect, the test fuel was changed to 30 ppm sulfur after the 300 ppm sulfur tests. The emission level did not recover to that of the initial 30 ppm sulfur during three repeats of the FTP. The effect of sulfur poisoning persisted more in the LEV than in the Tier 1 or TLEV vehicles.
Second, the effect of distillation properties, T50 and T90 on exhaust emissions also was investigated. Both T50 and T90 had large effects on exhaust emissions. Increasing T50 and T90 caused increasing exhaust HC emissions. In order to confirm the effect of engine tuning for driveability on the exhaust emissions, a special engine computer that reduced the amount of fuel enrichment for driveability was prepared and replaced the commercial computer of the LEV. Using this LEV with reduced fuel enrichment, the effect of T50 was studied. When CA Phase 2 certification gasoline was used, HC and CO was lowered 51% and 71% respectively, compared to the LEV with unmodified fuel enrichment. When gasoline that has higher T50 and T90 than the CAP of CA Phase 2, was used, driveability worsened and exhaust HC emissions significantly increased.