The engine deposits withwhich operators are concerned have their source in what is commonly called sludge. Sludge is composed of carbonaceous matter (either from blow-by or from high-temperature cracking); asphaltenes (oxidized oil products); ash (mostly lead oxide and iron bromide where gasoline is used, metals from wear and corrosion and dust from the air); and moisture from condensation. All these component parts of sludge vary greatly depending on engine design, operating conditions, fuel and lubricant used.
The whole engine ina sense is a centrifuge and throws this variable called sludge to various parts of the engine. The dead spots collect most with the hottest portions covered with a brittle flint-like carbon or lacquer.
In high output engines run for extended periods of time, ring sticking limits the time of complete overhaul. It causes increased cylinder and ring wear. Contrasted to this are sludges formed under cold weather conditions. The difficulty is largely confined to equipment in intermittent operation under light load withmuch idling. Under these conditions much dilution and blow-by occur while water in excessive amounts condenses in the crankcase oils and forms emulsions.
The problem is one for the engine designer to stay within the limits of the organic compounds (lubricating oils and fuels) and the operators to stay within the limits for which their equipment was built. Then with the proper selection of fuels and lubricants, engine deposits can be controlled to a minimum.


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