Alternatives to Diesel Fuel in California: Fuel-Cycle Energy and Emission Effects of Possible Replacements due to the Toxic Air Contaminant Diesel Particulate Decision

Limitations on the use of petroleum-based diesel fuel in California could occur pursuant to declaration by the California Air Resources Board (CARB) that the particulate matter component of diesel exhaust is a toxic air contaminant subject to the state’s Proposition 65. It is the declared intention of CARB not to ban diesel fuel, per se, at this time. Assuming no total ban, Argonne National Laboratory (ANL) explored two feasible “midcourse” strategies that result in some degree of (conventional) diesel displacement. In the first case, substantial displacement of compression-ignition (CI) by spark-ignition engines occurs and diesel fuel remains admissible for ignition assistance as a pilot fuel in natural gas–powered heavy-duty vehicles. Daily gasoline demand in California increases by 32.2 million L (8.5 million gal) overall, about 21 percent above the 2010 baseline demand projected by California’s energy and environmental agencies. Daily natural gas demand increases by 13.6 million diesel L (3.6 million gal) equivalents, about 7 percent above projected (total) consumption level. In the second case, CI engines utilize substitutes having similar ignition and performance properties for petroleum-based diesel. For each case, ANL estimated localized air emission plus generalized greenhouse gas and energy changes. Fuel replacement by dimethyl ether yields the greatest overall reduction in nitrogen oxide emissions. All scenarios bring about fine particulate matter (PM₁₀) reductions relative to the 2010 baseline, with greatest reductions from the CI-displacement case and the least from fuel replacement by Fischer-Tropsch synthetic diesel. Institutional and cost implications of vehicle and engine replacement were not formally evaluated.