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Providing a reliable hot surface ignition system (glow plug, GP) for natural gas-direct injection engines is challenging. This paper presents experimental results of aging all-ceramic Si3N4-based GPs in an engine, continuing previously published results on electric and gas burner rigs. The microstructural modifications of the ceramic heater, leading to degradation and ultimately to failure, are effected by four synergistic mechanisms: electrical, chemical, mechanical, and thermal. GP lifetime in engine follows the general Arrhenius law, with activation energy of 5.2 eV, (vs 9.1 V on burner rig and 13.8 eV on electric rig, as reported previously), suggesting additional factors contributing to GP failure in the engine.

In the development of advanced natural gas and hydrogen direct injection combustion engines, a challenge is providing reliable hot-surface (glow plug, GP) ignition systems; most promising are GPs with silicon nitride-based heaters. This paper presents experimental results of accelerated degradation tests of the GPs on natural gas-burning rig, continuing previously published results on GP degradation in air. Degradation, ultimately leading to GP failure, occurs through the synergistic effects of electric field and chemical reactions in the combustion environment. The resulting microstructural modifications of the ceramic heater, studied by SEM/EDS, are a combination of sintering additive ions migration and surface oxidation.

All-ceramic glow plugs (GP) based on sintered-silicon nitride are evaluated as hot surface ignition systems for natural gas and hydrogen direct injection combustion engines. This paper presents experimental results of the accelerated degradation tests of the GPs in air, wherein GP is heated solely by dc electricity. The complex degradation process has been linked mostly to the redistribution of the sintering additives in Si3N4/Yb2O3 system under an influence of dc electric field and temperatures over 1300°C, as experienced by GP in-service. Ytterbium ions migration varies with time, temperature, and voltage. The microstructural damage was studied primarily by SEM microscopy.