Performance of Vehicle Engines on Heavily Leaded Fuels

Abstract

Production problems on exhaust valves for vehicle engines, created as a result of the introduction of heavily leaded fuels during the 1939–45 war, resulted in the Ministry of Supply commencing research in 1948 to ensure that existing engines in civil and military vehicles would operate satisfactorily on a fuel containing 3.6 cu. cm. tetraethyl lead per Imperial gal. (T.E.L./I.G.)

Road tests at the Fighting Vehicles Research and Development Establishment at Chertsey, Surrey, were planned to establish the form of initiation of valve failure, which, in almost every instance, was found to be due to the partial seizure of the valve in its guide through fouling by overheated products of combustion. All modifications were, therefore, directed towards reduction of exhaust valve and guide temperatures, and the dispersal of combustion products.

Although fuels containing tetraethyl lead possess lead scavenging agents, nevertheless lead compounds form a large percentage of the deposits which accumulate on the surfaces of the combustion chamber and valves, and it is this increase in bulk, rather than the nature of the deposits, which appears to have the major effect on engine deterioration.

Modifications on the various engines differed considerably. Coolant systems were modified wherever possible and valve design amended. Changes involving major components such as cylinder blocks and cylinder heads, although desirable, were inappropriate to the programme. Design features on new engines directed towards reducing operating temperatures where they were highest should ensure much longer exhaust valve life on heavily leaded fuels.