TM 5-3895-383-24 In the USA, a 0.05 percent limit on the amount of fuel sulfur in diesel  fuel  was  mandated  in  January  of  1994  for  on-highway trucks.  The removal of sulfur from diesel fuel helps to reduce particulate emissions from diesel engines.  While limits for fuel sulfur have not generally been mandated for off-highway use, some   local   governments   have   regulations   that   include   off- highway use.  There is frequently no difference in the fuel that is sold for different applications.  The same fuel is often used for both on-highway applications and off-highway applications. Other    areas    of    the    world    are    mandating    similar    limits. Regulations  continue  to  become  more  stringent  Lower  sulfur limits can be expected in the future. The  fluid's  lubricity  describes  the  ability  of  the  fluid  to  reduce the friction between surfaces that are under load.  This ability reduces the damage that is caused by friction.  Fuel injection systems rely on the lubricating properties of the fuel.  Until fuel sulfur  limits  were  mandated,  the  fuel's  lubricity  was  generally believed to be a function of fuel viscosity. The process that is most commonly used to remove sulfur from fuel is called hydro-treatment.  This process is also the most economical   process.      Each   source   of   crude   oil   contains different amounts of sulfur.  Crude oils with low sulfur require little  hydro-treatment  to  obtain  the  0.05  percent  limit.    Crude oils with high sulfur require a more severe treatment. The Hydro-treatment removes the fuel's sulfur as well as other components.    The  treatment  removes  nitrogen  compounds, polar  materials,  bicyclic  aromatics,  polycyclic  aromatics,  and oxygen compounds.  While the removal of sulfur has shown no detrimental    effects    on    the    engine,    the    removal    of    other compounds have lowered the lubricity of the fuel.  As a result of     the     lowered     lubricity,     the     fuel     is     less     tolerant     of contamination by water and dirt.  The lower fuel lubricity can be seen as abrasive wear of fuel system components.  Fuels that have  a  low  lubricity  may  not  provide  adequate  lubrication  to plungers,  to  barrels,  and  to  injectors.    This  problem  may  be compounded in areas that require winter blends of fuel.  The lighter winter fuel blend has the following characteristics:  lower viscosity, lower cloud point, and lower pour point. All  low  sulfur  fuels  do  not  have  a  low  lubricity.    The  fuel's lubricity may be enhanced with additives.  Many fuel suppliers teat  the  fuel  with  these  additives.    Do  not  use  a  fuel  lubricity additive    before    you    consult    the    fuel's    supplier.        Some aftermarket additives may not be compatible with the additives that are already in the fuel.  Some additive packages that are supplied    by    the    aftermarket    manufacturer    may    not    be compatible  with  the  seals  that  are  used  in  fuel  systems  of some   diesel   engines.      Other   additive   packages   that   are supplied  by  aftermarket  manufacturers  cannot  provide  proper performance in high temperature conditions.  These additives may  leave  deposits  because  of  the  high  temperatures  that exist in the fuel systems of diesel engines. Maximum life of the fuel system can be achieved by performing the following tasks:  using a reliable fuel supplier, performing proper    maintenance    of    the    fuel    system,    and    installing Caterpillar high efficiency fuel filters in the fuel system. NOTE: Lighter    fuels    are    frequently    used    in    arctic temperatures.        These    lighter    fuels    are    the following fuels:  Jet A-1, JP-8, JP-5, and kerosene. The  fuel  lubricity  is  not  a  requirement  for  these fuels.      Do   not   assume   that   a   fuel   meets   the minimum specification.  Contact the fuel supplier for proper recommendations on fuel specifications (lubricity). Viscosity The viscosity of the fuel is significant because the fuel serves as a lubricant for fuel system components.  Arctic fuels should have   sufficient   viscosity.      The   fuel   must   lubricate   the   fuel system at a temperature of 0°C (32°F) or below freezing.  If the kinematic viscosity of the fuel is lower than 1.4 cSt as supplied to  the  fuel  injection  pump  or  to  the  unit  injectors,  excessive scuffing and seizure can occur. Cetane Number The  cetane  number  of  the  fuel  has  an  effect  on  the  ability  of the engine to start.  Also, the cetane number has an effect on the    interval    of    time    before    the    engine    runs    smoothly. Generally, an increase of ten in the cetane number will allow the engine to be started at a lower temperature.  The starting temperature  can  be  improved  approximately  7  to  8°C  (12  to 15°F) for every increase of ten in the cetane number.  After the engine reaches the normal operating temperature, a change in the cetane from 40 to 50 will have a minimum effect on engine performance. Maintenance Section Fuel Specifications 1-34