Causes and Cures of Oil-engine Smoke
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WITH the increasing attention which is being devoted to air pollution, the oil engine has been criticized in many quarters.. The causes and cures of heavy smoking from the exhaust of oil engines have been the subject of research by the Mobil Oil Co., Ltd., who have published their findings in the form of a memorandum.
On the matter of carbon-monoxide content, about which there have been many conflicting and erroneous .statemerits, the memorandum says tliat the exhaust fumes from a well-maintained oil engine contain a very low concentration of this gas.
The percentage varies with the design and adjustment of the engine, but because an oil engine operates with excess air at full torque, with correspondingly greater amounts of air at part torque, there is normally only a trace of carbon monoxide in its exhaust_
Fuel properties which could conceivably have an influence on oilengine exhaust smoke are given under seven heading s—specific gravity, volatility, viscosity, composition, cetane number, sulphur and carbon residuc. From these, the fuel property which would appear to have the greatest influence on " cold smoke" is that of volatility. (Cold smoke is the term used by Mr. P. H. Schweitzer, whose paper, "Must Diesel Engines Smoke?", was presented in 1947.) The most common mechanical faults likely' to cause the trouble, states the memorandum, are over-loading, running the engine too cool, tow compression pressures, dirty or defective injectors, incorrect governor adjustment, incorrect setting of the injection pump, incorrect injection timing and the misuse of excess-fuel devices.
A cooling-water temperature near the 190° F. mark aids in reducing cold smoke. Taking a broad view, it is contended that exhaust smoke can he reduced to a minimum by maintaining the engine and injection equipment in good order and, secondly, by keeping up the water temperature.
Within the range of fuels normally used, fuel characteristics can he significant, but are often subordinate to the foregoing features.