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A series of paired fuel tests were conducted comparing certification-grade highway diesel fuel with 5 to 50 vol% soy-methyl-ester biodiesel blends. Each fuel pair was tested for up to seven transient cycles representing various load conditions, using a 2006 model year Cummins ISB compression ignition engine equipped with exhaust gas recirculation. Except for the most lightly-loaded cycle, the results show statistically significant differences in NOx emission for all fuel pairs. The average NOx emissions due to biodiesel increased over each cycle, ranging from 0.9 to 6.6% and from 2.2 to 17.2% for the B20/B0 and B50/B0 fuel pairs, respectively. Significant reductions in CO and PM were observed over a majority of the cycles tested. The data also reveal that the change in NOx emissions increases linearly with the average cycle load. To complement the transient results, a single modal point was monitored daily to investigate biodiesel effects on engine operating parameters.

A production, direct injection diesel engine was modified to incorporate BP Oil's novel variable compression ratio (VCR) engine concept. The operation of the VCR mechanism was demonstrated and the performance and emissions potential of the concept evaluated. The VCR prototype achieved twice the specific power output of the baseline turbocharged, aftercooled engine. Its exhaust smoke emissions at high load were consistent with conventional direct injection (DI) diesel engines using equivalent fuel injection equipment. Light load particulate emissions and high load fuel consumption indicated a need for further development of the combustion system. Unexpectedly low HC emissions were achieved considering the large crevice volumes in the combustion chamber of the prototype engine. Likewise, exceptionally low NOx emissions were demonstrated. It is believed that the low HC and NOx emissions could be inherent features of the unique combustion system configuration.

In 1995, US Environmental Protection Agency (EPA) formed the Heavy-Duty Engine Working Group (HDEWG). The objective of the group was to assess the role diesel fuel could play in meeting exhaust emission standards proposed for model year 2004+ heavy-duty diesel engines. The group developed a three-phase program to achieve this objective. This paper describes the development of test fuels used in Phase 2 of the EPA HDEWG Program to investigate the effect of fuel properties on heavy-duty diesel engine emissions. It discusses the design of the fuel matrix, reviews the process of test fuel preparation and presents the results of a multi-laboratory fuel analysis program. Fuel properties selected for investigation included density, cetane number, mono- and polyaromatic hydrocarbon content.