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The Harmful Effects Of
Engine Soot
Engine soot is a common byproduct in internal
combustion engines, formed as the result of incomplete fuel combustion. Most
fuels are composed of hydrocarbons, containing both carbon and hydrogen, and
when undergoing complete combustion, the only byproducts are carbon dioxide and
water. However, no engine is completely efficient and complete combustion does
not occur. Complete combustion would require a very lean ratio of fuel to air,
whereas real engine conditions exhibit richer fuel mixtures. The less air that
is present in the ratio, the more favorable the conditions for soot
accumulation.
Soot formation is more pronounced in diesel
engines than gasoline engines due to the ways fuel is injected and ignited.
While fuel is injected during the intake stroke and ignited with a spark in
gasoline engines, it is injected during the compression stroke and ignited
spontaneously from the pressure in diesel engines. Combustion is more efficient
in gasoline engines because the air and fuel have a chance to thoroughly mix,
while the late fuel injection in diesel engines produces fuel-dense pockets in
the combustion chamber that produce soot when ignited. Newer exhaust gas
recirculation (EGR) diesel engines, designed to reduce NOx emissions by routing
part of the engine’s exhaust stream through an intercooler and back to the
intake manifold, further compound soot problems in diesel engine oils.
Excessive soot formation in oil can be caused
by a number of factors. Worn out rings or injectors, excessive idling, poor fuel
spray patterns and incorrect air-fuel ratios are major causes of soot formation.
A faulty fuel nozzle may spray more fuel than desired, increasing the
fuel-to-air ratio and causing incomplete combustion and soot accumulation, or
the air filter may become clogged, decreasing air supply and increasing the
fuel-air ratio.
Soot particles are spherical in shape and 98
percent carbon by weight. They are a very small size of around 0.03 microns, but
they often agglomerate to form larger particles. Although the majority of soot
produced during combustion exits through the exhaust, some passes through the
rings of the combustion chamber and enters the engine oil. As long as these soot
particles remain suspended in the oil and are not allowed to agglomerate, they
pose little risk to engine parts. It is up to the motor oil’s dispersants to
keep soot particles dispersed. However, in high soot conditions, dispersants can
become quickly depleted.
High soot load conditions lead to loss of oil
dispersancy as an oil’s dispersant additives are consumed. As dispersancy is
lost, soot particles agglomerate and form larger particles that build up on
engine surfaces. This soot and sludge eventually impedes oil flow, and it can
also form on oil filters, blocking oil flow and allowing dirty oil into the
engine. In addition, high soot levels within a motor oil increase its viscosity,
further impeding oil flow and increasing engine wear. Anti-wear additive
performance is also affected in high soot conditions as additives are gradually
removed from the oil by adsorption to soot particles, leading to increased wear
and premature engine failure.
Another negative effect of high soot
conditions is the formation of carbon particles on the piston ring grooves,
causing degradation of the oil seal between the ring and cylinder line and
abrading the ring and liner. As the gap between the ring and liner increases,
combustion byproducts such as gases and unburned fuels blow into the crankcase,
a problem known as blowby, eventually causing expanding gases to lose ability to
push the piston down and generate the power necessary to propel the
vehicle. Horsepower is lost and fuel efficiency decreases. Ring sticking and poor
heat transfer from the piston to the cylinder wall can also result.
AMSOIL synthetic diesel oils are formulated
with robust additive packages that effectively disperse soot particles so they
do not agglomerate and cause engine damage. In actual on-highway heavy-duty
truck field trials, at soot levels as high as 10 percent volume and higher,
AMSOIL diesel oils maintained an extremely low viscosity of 17 cSt. Excellent
wear control was maintained with an average iron content under 50 ppm.
AMSOIL
diesel oils provide outstanding protection against viscosity thickening and soot
generated wear.
T's Advanced Synthetics
Greg and Marcy Thurman
Your Nationwide
AMSOIL
Authorized Independent
Dealer
Nationwide US Warehouses,
Canada and Palm Harbor, FL
727-798-8552
E-Mail:
greg@tsadvancedsynthetics.com
If you
experience problems or have questions or comments about
our website please email us at
greg@tsadvancedsynthetics.com
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