During gas engine operation, a product failure mode exists: abnormal precious metal particles appear at the spark plug electrode gap, causing the electrode gap to narrow, resulting in a decrease in ignition voltage. In extreme cases, the electrodes directly short-circuit to a voltage of 0. This is reflected in the gas engine control panel parameters as decreased cylinder temperature and ignition failure.

Testing revealed that the abnormal particle material is composed of the precious metal body material of the spark plug electrode.

During service, the spark plug electrode is subjected to a complex environment of high temperature, oxygen, electro-corrosion, sulfur corrosion, and water vapor. Hydrogen sulfide (H₂S) in the fuel gas reacts with the precious metal electrode under the combined effects of high temperature and electric arc, forming a thin reaction layer on the electrode surface at the nanometer to submicron scale. The main components are platinum sulfide (PtS) and iridium sulfide (IrSₓ), accompanied by small amounts of platinum oxide (PtO₂) and iridium oxide (IrO₂). The reaction layer is porous and brittle, exhibiting extremely poor adhesion to the electrode substrate, which is the fundamental reason for the detachment of precious metal particles from the electrode surface.

At the instant the precious metal reaction layer peels off the electrode surface, under the influence of high temperature and a strong reducing atmosphere (rich in CH₄, H₂, and CO) within the gas engine, the peeled reaction layer is directly reduced to the precious metal element. The core reduction reactions are as follows:

PtS + H₂ → Pt (elemental) + H₂S↑

IrSₓ + H₂ → Ir (elemental) + H₂S↑

PtO₂ + CO → Pt (elemental) + CO₂↑

IrO₂ + CO → Ir (elemental) + CO₂↑

The freshly reduced platinum/iridium element is in droplet form, in a liquid or semi-molten state. Driven by the vortex in the pre-combustion chamber, these droplets will re-adhere to the electrode surface (the wetting effect of the same metal at high temperature makes the droplets bond extremely firmly to the electrode). If the droplets happen to adhere to the electrode gap, it will directly cause the aforementioned ignition failure.

Sulfur plays a crucial role in accelerating electrode corrosion and particle flaking/remodeling. The extent of its impact is determined by the sulfur content during gas combustion, which the industry generally controls to below 20 ppm. Besides sulfur, other key factors inducing precious metal particle formation include high electrode temperature and gas engine knock.

High electrode temperature is often caused by an excessively low spark plug heat range, preventing timely heat dissipation from the spark plug electrode, a product compatibility issue. When analyzing this type of failure, spark plug heat range compatibility should be prioritized: if most users of the same unit do not experience this failure, spark plug design issues can be largely ruled out; if the failure is widespread in the same unit, design optimization is needed to reduce electrode temperature (optimization encompasses ceramic heat dissipation structure, electrode construction, etc.).

Spark plug and unit compatibility issues make the probability of failure highly correlated with unit load: if the unit operates at low load for extended periods, ignition failures caused by precious metal particles are generally unlikely.

In response to this type of failure, in addition to reducing the electrode temperature at its source through design optimization, increasing the electrode gap is a temporary measure that can be taken.