Failure analysis of diesel engine glow plugs

Abstract

The implementation of start-stop technology in modern cars requires improvements of several elements of the internal combustion engine start-up system. In the present study, we have been focused on the failure phenomena of diesel engines glow plugs and attempts to extend their lifespan. The investigation revealed that the most sensitive element of the glow plug is a heating coil made of FeCrAl (Kanthal AF®) wire. Despite excellent anti-oxidation properties of these alloys, provided by the formation of a protective alumina scale on the alloy surface, the oxidation resistance is limited when exposed to thermal cycling up to 1050 °C. The reason is cracking and constant re-formation of the alumina protective scale and consequent consumption of the aluminium in the subsurface area of the wire. To prevent premature failure of heating coils, powder pack aluminization was implemented to increase the aluminium content in the subsurface of the alloy and thus the possibility of easier re-formation of the protective alumina scale. Phenomena that lead to failure of the glow plug were studied by X-ray computerized tomography (CT), optical microscopy (OM), scanning electron microscopy (SEM-EDXS), and microhardness measurements (HV). Comparison between aluminized and untreated samples is outlined and microstructural changes during thermal cycling and isothermal annealing discussed.