1925-01-01

NOTES ON CRANKCASE CORROSION 250031

There is almost unanimous agreement that water in the crankcase is responsible for corrosion in internal-combustion engines. The quantity of water present in the products of combustion of the fuel is dependent upon the hydrogen content of the fuel, the mixture-ratio and the humidity of the air that enters the engine. The amount of water that may be condensed on the cylinder-walls or in the crankcase depends upon the effectiveness of the pistons and piston-rings in preventing gas leakage, the temperature of the cylinder-walls and crankcase and the extent of the breather action. The relative freedom of some engines from water accumulation is due to their higher operating-temperatures or to the better interchange of air by breather action which results in dilution of the gases in the crankcase and consequent reduction of the saturation temperature of the gases.
Water alone will cause corrosion but the action may be accelerated by the formation of weak sulphurous or sulphuric acid. A reduction of the sulphur content of fuels is desirable but, even with more insistent demand for such reduction, time would be required to bring this about. The chemical activity resulting from this and other contaminants would be negligible if the formation of water were controlled effectively. Other troubles for which water is responsible would also be eliminated.
Much can be accomplished toward prevention of water accumulation by developing pistons that will reduce blow-by and retain their effectiveness in use. In addition, means should be provided to (a) reduce the warming-up period and maintain the crankcase temperature sufficiently high to prevent condensation and eliminate water from the oil, and (b) ventilate the crankcase. Water formed during the starting of the engine will thus be minimized and ejected later and only a small amount of vapor will be present in the engine when it is stopped.
Either air or steam-cooling, with provision for controlled heating of the crankcase, is favorable for the solution of this problem. The passing of preheated air through the crankcase has marked advantages. In existing equipment, radiator shutters and thermostatic control of the jacket-water temperature, continuous-oil-heating devices, oil-filters and ventilating will all contribute toward averting trouble. Methods that may be used for preventing condensation of water in engines also will reduce oil-dilution and effect a more efficient utilization of fuel and oil.

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