Page 8 - Schroeder - Fuel Filtration

The New World of Advanced Diesel Filtration

Past Practice
Separation of emulsified water from diesel fuel is a long standing requirement for diesel engine
operation. Water removal has been traditionally performed by a fuel-water separation filter mounted
in the engine fuel system or, in tough operating
environments where downtime has been managed by
implementing best practice fluid maintenance, as part
of the bulk tanks staged filtration at the dispensing
system. The most typical filtration media found in such
separators is a single resin impregnated hydrophobic
barrier, such as silicone treated cellulose. This media
separates water on its water repellent surface. Water in
the fuel is rejected and beads up on the upstream side
of the barrier media. As more water is rejected, beads
coalesce into large drops, and drain into a collection
cup while the fuel passes through a port located above
the sump.

There are often unintended outcomes when a process or specification change is made. The changes to
diesel engines and diesel fuels provide no exception to this rule. The transition to ultra-low sulfur diesel
(ULSD) provides a specific example.

In order to meet mandated sulfur levels, ULSD is subjected to refining processes that removes not only
the sulfur but also the inherent lubricity of the original higher sulfur diesel. The result is the ultra-clean
fuel. Unfortunately, it is an ultra-clean fuel that has been stripped of its native lubricity. Fuel lubricity
is critical as it is the fuel’s lubricity that is one area protecting the injection systems from catastrophic
wear and precise control of combustion. A fuel system must hold pressure in order to inject fuel into the
cylinder. Wear induced leaks can lead to engine failure due to fuel starvation.
As lubricity deficiencies were surfacing with early ULSD adoption, biodiesel production and the push to
use biodiesel began to take hold in the North American diesel market. Biodiesel improved ULSD lubricity,
and as a result, generated some independent motivation for its use as a blended lubricity component of
diesel fuel. The additional perceived need for a domestic or “green” fuel supply, and pressure to minimize
fossil carbon emissions have prompted governments mandate a percent of biodiesel in diesel blends.
Just as the processing of ULSD produced unforeseen side effects in diesel fuel lubricity, the failure of
existing fuel-water separators to react to the changing needs became apparent. With the lubricity
additives the ULSD blends containing biodiesel, created conditions where the industry standard
commercial fuel-water separators failed to remove 40-100% of fuel-entrained water. The side effect is
now typically 40% more water downstream of the filters that in the past worked at a 90% efficiency.
Meanwhile there is no way for an operator to know it is happening unless the effects are drastic and
observed and questions asked. Unlike particle filters, which generate pressure differentials prior to
by-pass alerting the operator to the end of the element life, there is nothing that communicates to the
operator that the fuel-water separator is not removing water. Fuel-water separators rely on an operator
or auto-valve to empty a water to a collection chamber when the housing is partially full. If the collection
chamber does not fill up, it is not an indicator of fuel-water separator failure; rather it is an indicator of
dry fuel. The result is the fuel-water separator can be passing the water continuously into the injection
system without the operator’s knowledge.

8 SCHROEDER INDUSTRIES | FUEL FILTRATION