Application of a diagnostic technique for evaluating the quality of the air–fuel mixture and the ignition quality of a spark-ignition reciprocating aircraft piston engine

The performance characteristics of an aircraft piston engine are affected mainly by the air–fuel mixture quality (i.e. condition of the fuel injection system) and by the spark timing and spark duration (i.e. condition of ignition system). Thus, the present work focuses on investigating the effect of both fuel injection and spark ignition systems on performance characteristics of two aircraft piston engines which are of the same type but have overhauled by two different workshops. The investigation is conducted by applying an existing diagnostic technique, which is based on the simultaneous recording and processing of two electric signals: one corresponding to cylinder pressure and the second corresponding to the ignition system. The basic characteristics of the proposed methodology are simplicity and field applicability on engines of this type. A detailed experimental investigation has been conducted on the aforementioned two aircraft piston engines on a dedicated test bench. From the results, it is revealed that the proposed diagnostic methodology provides reliable information for the effect of both the ignition and fuel injection systems on engine performance characteristics. The results derived from the specific work enable the comparative evaluation of the engines and their ignition and fuel injection systems. Finally, based on this first investigation, the proposed methodology seems to be promising, because it can be easily applied on any type of spark-ignited engine and especially on aircraft piston engine, where due to its geometry and multicylinder nature, the application of lab techniques on the field is, if not impossible, extremely difficult.