Exhaust Valve Life in Small Industrial Gasoline Engines

Abstract

The small industrial gasoline engine of 1 to 10 h.p. presents difficulties in ensuring an adequate exhaust valve life, which are not present to the same extent with the automotive engine. Thus, these engines often operate under a continuous full-load duty which does not permit combustion chamber deposits to clear themselves as readily as does the fluctuating load of the vehicle engine. The fact that so many of the industrial engines are single-cylinder units means that one piece of deposit under an exhaust valve may bring the engine to a halt, whereas in the multi-cylinder vehicle engine, the unaffected cylinders would generally pull the engine round until the deposit had cleared itself. Consequently, when the operating conditions of the valve are made more severe by increasing the lead content of the fuel, the industrial engine is particularly vulnerable.

The investigation described in this paper was carried out on five assorted water-cooled and air-cooled engines to establish the minimum modifications necessary to enable them to run for 1,000 hours between top overhauls using M.T. 80 fuel containing a maximum of 3.6 cu. cm. tetraethyl lead per Imperial gal. (T.E.L./I.G.). In addition to being the Services fuel, M.T. 80 can be regarded for this purpose as representative of the most highly leaded gasoline likely to be marketed commercially in the immediately foreseeable future. Under standard conditions, the water-cooled engines failed in 210–270 hours' full-load operation, and the air-cooled engines in 65–80 hours, owing to sticking of the valve stem in its guide.

The tests and modifications are described in considerable detail. Although in general 1,000 hours' operation can be obtained on all these engines with comparatively simple modifications, premature failure was always liable to occur in a random manner, owing to deposits showering down into the cylinder. This situation would seem difficult to overcome by mechanical design alone. Some preliminary results of an approach from a chemical aspect, using additives in the fuel, and various additive and non-additive lubricants, are described.