Numerical Simulation Study on the Influence of Spark Plug Position on Combustion Performance of a Cycloidal Rotary Engine

Abstract

Abstract. The spatial positioning of ignition significantly governs combustion behavior in cycloidal rotor engines, with its optimization being paramount for enhancing operational performance and extending service durability. This investigation employs computational fluid dynamics (CFD) coupled with chemical reaction kinetics to develop a validated numerical model replicating in-cylinder thermofluid dynamics, systematically evaluating 90 distinct ignition configurations for performance optimization and structural design guidance in cycloidal rotor engines. Analysis reveals a pre-combustion SCL (streamline convergence line) within the combustion chamber that critically modulates ignition site selection through its aerodynamic interactions. The tested ignition configurations exhibited significant variation in maximum cylinder pressure, with the optimal configuration achieving a 191.32% pressure elevation over baseline conditions and an 8.19% enhancement compared to conventional designs. Crucially, ignition positioning dictated the crank angle phasing of peak pressure occurrence, where combustion efficiency optimization was attained when maximum pressure aligned with crank angles (CA) between 17.5-CA and 25.5 °CA. Furthermore, the ideal ignition zone was non-centric, localized within the NⅡ–NⅢ region spanning 1/5 to 4/5 of the chamber width from the wall boundaries, intersected by the SCL's primary flow path while maintaining critical clearance from chamber walls. These findings establish both theoretical framework and technical guidelines for performance enhancement in cycloidal.