Don’t let soot spoil the performance of your equipment
Part Two: Science of Soot and its relationship with engine oil
Techenomics has the expertise to find the reason and provide treatment.
Soot is carbonaceous particle generated by incomplete combustion of fuel. It is harmful to engines and if left to accumulate can impact on productivity through poor performing components.
Techenomics oil analysis and fluid management expertise is an important tool in overcoming the problem and preventing costly equipment breakdown.
Mechanism of Soot Generation
Generation of soot particles in a diesel engine have two hypothetical pathways.
Elementary Carbon Hypothesis describes that the fuel dissociates at high combustion temperatures, i.e. breaks down into its basic elements of carbon and hydrogen. Hydrogen molecules diffuse in the oxygen-rich environment significantly faster than the larger carbon atoms. Their quadruple valences enable them to form clusters, primarily hexagonal and pentagonal structures, very quickly when they are deoxygenated. Curved shells form and grow to typical particulate sizes of approximately 10 nm within milliseconds.
While Polycyclic Hypothesis assigns critical importance to ethyne (formerly known as acetylene C2H2). Ethyne is formed by pyrolysis - the decomposition of fuel under O2 exclusion - of aliphatic and aromatics while cleaving hydrogen.
Assuming the structure is polycyclic, repeated bonding of ethyne molecules can cause a graphitic structure to grow. The occasionally quintuple rings curve the macromolecules produced. Several of these molecules accrete in layers atop one another, producing primary particulates. The primary particulates produced typically have a size of 2-10 nm.
Why is this a problem?
The resulting soot typically consist of carbon, ash, and unburned hydrocarbons. They are either exhausted into the atmosphere or absorbed by the engine's lubricant. However, the majority of soot particles are oxidized prior to exhaust and retained by the lubricant. It is then transported around the engine and causing a variety of problems.
Soot can produce significant amounts of engine wear through abrasion (soot particles preferentially adsorbing anti-wear species within the lubricant), lube starvation (higher level of soot contamination), and corrosion (High concentrations of soot can increase the local acidic level and, around the piston where high temperatures and volatile gases coexist).
At excess levels, soot causes abrasion and high wear in engines and mechanical components. Various wear mechanisms manifest themselves as a function of particulate size and distribution.
Particulates > 20 µm are now generally filtered out since they cause unduly high wear in basic and connecting rod bearings, piston rings, cylinder barrels and gears. Particulates of 0.5 to 5 µm alone cause more than 50% as much wear as larger particulates. If soot particles form clumps, can result in valve train, ring and liner wear.
Sahar our Newcastle Laboratory Manager and George Li will further discuss the impact of soot on lubricant viscosity and the result of Blow by and filter blockage in our third soot article.
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