Influences of a new glow plug shield on natural gas combustion characteristics in direct-injection engines

Use of a shielded glow plug (GP) for ignition assist enables operation of direct-injection engines on 100% natural gas. The shield improves ignition performance by reducing GP cooling from impinging intake air and injected natural gas jets and by trapping mixture adjacent to the hot surface thereby increasing residence time. After ignition, flame must propagate out of the shield to consume fuel in the combustion chamber. The number, size, and position of openings in the GP shield determines the path of flame propagation from the shield. This study computationally investigated the performance of a shield with multiple openings arranged in a diamond pattern compared to a basic single-opening shield. A KIVA-3V based engine model coupled with the CANTERA kinetics package was used and incorporated a multi-step phenomenological soot model to predict the formation of soot particles. The results illustrate that the new multi-opening shield has significant influence on both the flow of injected fuel into the shield and the flame propagation out of the shield. The multi-opening shield design reduces the fuel flow into the shield during injection and improves fuel distribution within the shield compared to the single-opening shield. With the multi-opening shield, the initial flame propagating out moves towards the combustion chamber wall to consume the adjacent fuel jets before spreading in the swirl direction. Both shields result in comparable pressure rise, but the multi-opening shield reduces overall soot emissions by 46.6%, with similar methane emissions, compared to the single-opening shield.