Combined influence of ignition chamber volume and spark plug channel diameter on the performance of small-scale natural gas Wankel rotary engine

Abstract

To improve the poor in-cylinder combustion condition of the small spark ignition Wankel rotary engine (SI-WRE) and improve its efficiency, this paper conducted a comprehensive optimization of its ignition environment. Since there are no known effects of ignition chamber characteristics, including ignition chamber volume ( $ V_{ic} $ ) and spark plug channel diameter ( $ D_{spc} $ ), on the ignition environment, various combinations of $ V_{ic} $ and $ D_{spc} $ were established, simulated, and compared, using Computational Fluid Dynamics (CFD) methods with validated models. As there are small and complex structures in the small SI-WRE, along with the huge simulation load in the case study, special treatments were adopted in mesh division to maintain the fast and accurate simulation. The results showed a wide thermal efficiency range of 8.51–32.13% under various $ V_{ic} $ and $ D_{spc} $ combinations, indicating that the engine performance was deeply limited by the ignition chamber. $ V_{ic} $ and $ D_{spc} $ also had profound influences on short-term (affected by $ D_{spc} $ ) and long-term (affected by $ V_{ic} $ ) flow losses, fresh intake at spark region, combustion speed, and working stability. Stable working condition was achieved when $ V_{ic} = 1.5 $ cc and $ D_{spc} = 2 $ mm, while powerful situations were $ V_{ic} = 1.5 $ cc and $ D_{spc} = 8 $ mm, or $ V_{ic} = 0.5 $ cc and $ D_{spc} = 2 $ mm.

Keywords

• spark ignition wankel rotary engine (si-wre)
• ignition chamber
• spark plug channel
• ignition environment