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10
Chapter 4
DIESEL FUEL BASICS
Diesel fuel properties have changed in recent years due to
the way the product is processed today at the refi neries.
A couple of decades ago diesel fuel, gasoline, home heat-
ing oil among other distillation products were processed
by heating the crude oil. At different boiling tempera-
tures, various parts of the crude oil were evaporated then
condensed sending the fi nal products to storage tanks for
distribution. The distillation process generally produced
stable diesel fuel with a storage life of several months.
Around 50% of the oil left over from the distillation pro-
cess was designated as heavy fuel oil being used for ship’s,
power plants, and industrial products such as nylon, plas-
tics, and asphalt.
Refi ning crude oil
today has changed dramatically due
to increased demand for the product. A process called
“chemical cracking” has allowed the refi ner to extract
more of the lighter distillates from the crude oil leaving
about 16% of the residual as heavy fuel oils. Lowering the
diesel fuel sulphur levels due to environmental concerns
has led to further fuel instability. Due to these newer
methods of refi ning diesel fuel is far less stable than the
older distillation process.
There are different theorems on defi ning fuel system “al-
gae” and how it develops in the vessel’s fuel tank. Algae is
slang for the fungus that grows in fuel tanks.
One school of thought
isolates two of the key fuel compo-
nents. Asphaltenes and paraffi ns in this premise begin to
oxidize and re-polymerize forming clusters resulting in
fuel tank “algae”. As these clusters “grow” in size they
cling themselves to tank walls and baffl es.
Others state
that “algae” is formed when water condenses
in the boat’s fuel tank. Water can enter the vessel’s fuel
tank through the fuel pumping process at the fuel dock
since their tank may already be contaminated with algae-
micro organisms. Once inside the tank these algae-mi-
croscopic organisms from the plant kingdom are able to
combine with water and diesel to form tank sludge.
Keeping tanks free from water, dirt and micro organisms
is almost impossible, but luckily you can eliminate them
before they reach the engine and fuel injectors through the
use of primary and secondary fuel fi lters. Algae ends up
in the fuel system once the boat is running which breaks
up the tank “algae” and/or sludge into mini clusters.
Using diesel fuel in this condition may cause the follow-
ing:
• Fuel tank sludge-remove manually or by chemicals
• Dirty engine oil
• Shortened engine component life
• Smoke emitting from the engine exhaust system
• Carbon deposits in the engine
• Incomplete combustion
• Loss of power and performance
• Clogged primary and secondary fuel fi lters
• Malfunctioning fuel injectors
When this condition is present in the marine diesel fuel
system the fuel does not combust rapidly as it should re-
sulting in a loss of engine effi ciency.
Basically, with either school of thought this “algae” or
fuel tank sludge is the result of aging diesel fuel. It can
occur in as little as 60-90 days depending on the condi-
tion of the tanks and environment where the diesel fuel
is stored.