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This study is the second in a series of three EPA studies to investigate the effect of fuel reformulations and modifications on exhaust emissions. Both the first and second study in this series of studies were used to support the development of EPA's complex model for the certification of reformulated gasolines. Phase I of the study tested eight fuels on forty vehicles. This study, termed Phase II, tested twelve fuels on a separate fleet of 39 light-duty vehicles. The Phase II fuel parameters studied included Reid Vapor Pressure (RVP), the 50% and 90% evaporated distillation temperatures (T50 and T90), sulfur content, aromatics content, olefin content, oxygenate type and oxygen content. Measured exhaust emissions included total hydrocarbons (THC), oxides of nitrogen (NOx), carbon monoxide (CO), carbon dioxide (CO2), benzene, 1,3-butadiene, acetaldehyde and formaldehyde.

The Environmental Protection Agency (EPA) recently tested a clean diesel fuel developed by Dion & Sons for use in stationary sources. This fuel is known as Amber 363 in Southern California and its technology is licensed outside of the Southern California area to Shell Oil Products Company for use as a stationary source fuel. The fuel, hereafter referred to as “Shell LOW NOX Fuel,” was tested in a 1990 model year heavy heavy-duty diesel engine using both the transient Federal Test Procedure (FTP) for on-highway heavy-duty engines, the steady-state FTP for nonroad heavy-duty engines, and the steady-state generator set test cycle. For each test, EPA measured hydrocarbon (HC), carbon monoxide (CO), nitrogen oxides (NOx) and particulate matter (PM) emissions. Transient testing showed that the Shell LOW NOX Fuel lowers NOx, HC and PM emissions with no statistically significant change in CO emissions for both cold-starts and hot-starts when compared to diesel certification test fuel.

An exhaust carbon monoxide (CO) emissions model has been developed. This model uses the fuel properties oxygen content, sulfur content, RVP, olefin content, distillation parameters E200 and E300, and aromatic content to predict exhaust CO emissions. This predictive model is based on emissions measured under summer conditions. The model was developed using the same statistical techniques used to develop the exhaust VOC and NOx models (Complex Model) presented in the Environmental Protection Agency's (EPA) regulations for the final rule on reformulated gasoline. It is the objective in this work to briefly outline the procedure used to develop the exhaust CO model, to look at the behavior of the developed model, to examine the predictability of the developed model and to state the limitations of the model.