A common means to increase efficiency in stationary spark ignited engines is to operate the engine with a higher air/fuel ratio of the mixture in conjunction with a higher turbulence level; however, this generally leads to severe conditions that significantly impact the inflammability of the gas–air mixture and combustion stability. Because the electric arc that forms at the spark plug is a main influencing factor in combustion, detailed research work in the field of electric arc behavior generated at spark plugs is required. This article thus presents a specially tailored test rig that is designed to facilitate an investigation of electric arc behavior under cross-flows at a spark plug typically used in gas engines. The test rig consists of a closed flow circuit for inert gases; its centerpiece is a test cell that provides optical access for high-speed imaging of the electric arc behavior at the spark plug. The required flow velocity at the spark plug is set with a blower. Flow velocities up to 30 m/s, pressures up to 60 bar and temperatures up to 80 °C can be achieved inside the flow system at the location of the spark plug. Postprocessing algorithms have been developed to automatically extract information from the high-speed images. The results reveal that the arc stretches more at a higher flow velocity as indicated by its greater arc length. In addition, it is evident that the cycle-to-cycle variation in arc length increases at higher flow velocities. The secondary voltage history and its cycle-to-cycle variation are strongly influenced by the arc length. This is reflected in the cycle-to-cycle variation of the spark energy input to the flowing gas. These results support the conclusion that spark behavior itself can be a substantial source of cycle-to-cycle variation in the combustion process observed in spark ignited gas engines.
Robust engine operation with long maintenance intervals and low emissions is the key to meeting future engine requirements. At the same time, engines should be environmentally friendly, resource-friendly, and cost-effective to produce and operate.
To meet these market requirements, a central component in engine development is the ignition system and in particular the spark plug.
To increase the maintenance intervals of internal combustion engines, it is necessary to increase spark plug lifetime by reducing spark plug wear. The electrode materials used to date are often expensive and rare, and their mining is not without controversy.
Successful use of alternative spark plug electrode materials which are available in large quantities, inexpensive, and more resistant to wear than existing materials with similar ignition behavior would advance engine development so it can meet further economic and environmental requirements.
To this end, ceramic spark plug electrodes were investigated to determine their spark and ignition behavior as well as their wear. These materials seem to be an interesting alternative to existing spark plug electrode materials.
This paper presents a spark plug with ceramic spark plug electrodes that achieves conditions similar to those of standard spark plugs in terms of secondary voltage trace and ignition behavior. Furthermore, it introduces a sophisticated method for scientific, cost-effective, and application-oriented development.
Finally, it provides a promising outlook for the ignition behavior and combustion performance of engines with this spark plug.
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