Debate and research on changing disesel fuel to lower emissions has focused on several fuel
specifications, namely:

                            1.  Cetane level;
                            2.  aromatics content;
                            3.  fuel density;
                            4.  distillation characteristics (T90 and T95);
                            5.  oxygenates content; and
                            6.  sulfur content.

        Control of these parameters may have the potential to provide direct benefits by incrementally
lowering emissions whens the fuel is burned, although the benefit may vary depending on the sophis-
tication of the engine technology involved.

        Much of the available data... is for heavy-duty engines...These engines depend on exhaust gas
recirculation (EGR) and optimization of engine design...The result of this study showed these eng- ines were mostly insensitive to these [above-named] parameters... with reduced NOx emissions by only 10% due to a reduction in fuel density and aromatics content. Another study (EPEFE Report )
for both light- and heavy-duty diesels showed the largest impact on particulate emissions (by only
7% overall) were from lowering T95 and fuel density. Increasing the cetane number was found to
have no observable benefit... except on older-technology engines. The addition of oxygenates to
diesel fuel must be considered tentative "pending further investigative work."

Desulfurization of diesel fuel

        According to this report, "reducing the sulfur content of diesel fuel has the potential to provide
large indirect technology-enabling benefits in addition to some amount of direct emission benefits. In
fact, "sulfur reduction appears to be the only fuel change with potential to enable new technologies
needed to meet Tier 2 light-duty or anticipated future heavy-duty standards."  EPA-USA avers :
"at this point, we believe that sulfur-control is the most likely means of achieving cost-effective diesel
fuel emission reductions."
 

Potential Benefits of Reducing Sulfur

        Diesel fuel desulfurization should be evaluated primarily for its potential to enable new engine and aftertreatment technologies . These so-called sulfur-sensitive technologies may be categorized
as follows:

                        1.  electronically-controlled EGR as a means of reducing NOx emissions by as
                            much as 90% (especially for heavy-duty engines);
                        2.  various types of catalysts/catalytic converters (either active or passive types) for
                            removal of NOx by 15-30% on the average;
                        3. exhaust aftertreatment by the use of a ceramic or metallic filter (sometimes called
                            a 'soot filter'), or a particulate (PM) trap;
                        4.  oxidation catalysts, which reduce exhaust PM by removal of volatile organics and
                            hydrocarbons, using precious metals such as platinum;
                        5. SCRs (selective catalytic reduction) for 70-90% NOx reductions in stationary
                            engines but now being experimentally tested for mobile applications, utilising mix-
                            ture of urea and water;
                        6.  NOx storage catalyst system with a potential to reduce NOx by 50-75%; and
                        7.  continuously regenerating PM filter for light-duty application where the potential
                            for PM reduction is estimated at 80% or more.