The objective of this paper is to propose a new model in the identification of a contributing factor to the generation of Radio Frequency Interference (RFI) due to the operation of a spark-ignited engine. This model incorporates parameters in the electrical operation of the ignition system components and their interaction with the engine mechanical structure, which is also used as a circuit component (the ignition system “ground”). T he model was developed as a result of analysis of numerous studies that have been conducted over the years in an attempt to identify why RFI characteristics can differ when using identical components on different engines, or locating the components in different locations on identical engines. This situation is a problem due to the resulting uncertainty with respect to the determination of what is the optimum vehicle ignition system configuration to meet all electrical and RFI or electromagnetic compatibility (EMC) requirements. T he requirements may either be legislated or original equipment manufacturer (OEM) mandated requirements.
There has been an assumption made for many years by automotive system engineers that similar ignition system components should have similar RFI performance, regardless of the specific vehicle or engine application. Frequently however, this is not the case and it is many times attributed to variation in ignition component tolerances or even “unknown” ignition component characteristics. As a consequence, the RFI levels are typically not determined until vehicle testing is conducted, which by then is extremely late in a vehicle program.
In addition, many times the mechanical engineers working on the engine components are not advised of how the engine structure is used as an electrical path for the ignition system. This results in placement of the component on the engine due to packaging requirements, instead of EMC performance.