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The first round of Federal Test Procedure (FTP) emissions testing of variable-fuel ethanol vehicles from the U.S. Federal fleet was recently completed. The vehicles tested include 21 variable-fuel E85 1992 and 1993 Chevrolet Lumina sedans and an equal number of standard gasoline Luminas. Results presented include a comparison of regulated exhaust and evaporative emissions and a discussion of the levels of air toxics, as well as the calculated ozone-forming potential of the measured emissions. Two private emissions laboratories tested vehicles taken from the general population of Federal fleet vehicles in the Washington, D.C., and Chicago metropolitan regions. Testing followed the standard U.S. Environmental Protection Agency's FTP and detailed fuel changeover procedures as developed in the Auto/Oil Air Quality Improvement Research Program. Variable-fuel vehicles were tested on single respective batches of E85, E50, and California Phase 2 reformulated gasoline (RFG) blended specifically for this test program.

The U.S. Department of Energy (DOE) is committed to increasing our nation's energy security by decreasing our dependence on imported petroleum. The Fuels Technologies Subprogram within DOE's Office of Freedom Car and Vehicle Technology (OFCVT) supports research that allows the United States to develop advanced fuels that enable efficient engines with low emissions. This document reports the completion of NREL FY 2004 Annual Operating Plan milestone 10.2: "Report on the relationship between molecular structure and compression ignition fuels, both conventional and HCCI." This work is an incremental step toward the OFCVT Multi-Year Program Plan APBF/NPBF Milestone No. 3: "Establish fuel and lubricant constituents that are required for advanced combustion regime engines." We must understand the effects of fuel chemistry on ignition to develop fuels that enable more efficient engine designs, using both today's technology and future advanced combustion concepts. NREL has conducted two parallel activities aimed at understanding how molecular structure affects ignition properties. First, we developed an empirical tool to predict the cetane number (CN) of pure compounds with only the molecular structure as input. Then, we experimentally investigated the ignition properties of pure chemicals with varying functional groups. In the first activity, we conducted a comprehensive search of CN data in the published literature to understand how molecular structure affects compression ignition. This resulted in CN data for 275 pure compounds, including 147 hydrocarbons and 128 oxygenates. These compounds were then input into a Quantitative Structure Activity Relationship (QSAR) software package. Then we calculated a set of approximately 100 molecular descriptors from the molecular structure of each compound. These descriptors were based on the geometry, connectivity, functional groups, electrotopological state, etc. of the molecule. A genetic algorithm was used to determine which of the many possible descriptors was most relevant to model the CN. One comprehensive QSAR model could be derived for the entire database, but it was more effective to develop models from subsets of the database for specific classes of compounds. These included big classes such as hydrocarbons and oxygenates, and smaller subclasses such as cyclic compounds, saturated hydrocarbons, and esters. The QSAR models demonstrate the utility of a predictive model for CN using only the molecular structure as input. In the second activity, we experimentally investigated the impact of molecular structure on ignition properties with the Ignition Quality Tester. We measured the CN and how the ignition delay varies as a function of temperature. The results show that all hydrocarbon fuels tend to show approximately the same temperature dependence (when plotted on an Arrhenius plot). However, certain oxygenates (such as acetals) show a reduced temperature dependence. For example, dipropylene glycol monomethyl ether has a cetane number of 42 under normal test conditions (550...