Optical study on the effects of the hydrogen injection timing on lean combustion characteristics using a natural gas/hydrogen dual-fuel injected spark-ignition engine. (17th June 2021)

• Record Type: Journal Article
• Authors: Zhang, Ren; Chen, Lin; Wei, Haiqiao; Pan, Jiaying; Li, Jinguang; Yang, Penghui; Chen, Rui
• Is Part Of: International journal of hydrogen energy. Volume 46:Number 39(2021)
• Page Start: 20777
• Page End: 20789
• Publication Date: 2021-06-17
• Subjects: Optical high compression ratio engine -- Combustion high-speed photography -- Lean combustion -- Natural gas engine -- Hydrogen addition -- Dual fuel injection; Hydrogen as fuel -- Periodicals; Hydrogène (Combustible) -- Périodiques; Hydrogen as fuel; Periodicals; 665.81
• DOI: 10.1016/j.ijhydene.2021.03.171
• Languages: English
• ISSNs: 0360-3199

Abstract

Abstract: Lean combustion has the potential to achieve higher thermal efficiency for internal combustion (IC) engines. However, natural gas engines often suffer from slow burning rate and large cyclic variations when adopting lean combustion. In this study, using a dual-fuel optical engine with a high compression ratio, the effects of direct-injected hydrogen on lean combustion characteristics of natural gas engines was investigated, emphasizing the role of hydrogen injection timing. Synchronization measurement of in-cylinder pressure and high-speed photography was performed for combustion analysis. The results show that the direct-injected hydrogen exhibits great improvement in lean combustion instability and power capability of natural gas engines. Visual images and combustion phasing analysis indicate that the underlying reasons are ascribed to the fast flame propagation with hydrogen addition. Regarding the direct injection timings, it is found that late injection of direct-injected hydrogen can achieve higher thermal efficiency, manifesting advanced combustion phasing, and increased heat release rate. Specifically, the flame propagation speed is elevated by approximately 50% at −100 CAD than that of −250 CAD. Further analysis indicates that the improvement of engine performance is ascribed to the increased volumetric efficiency and in-cylinder turbulence intensity, manifesting distinct flame centroid pathways at different injection timings. The current study provides insights into the combustion optimization of natural gas engines under lean burning conditions. Highlights: Experiments were conducted on an optical SI engine with a high compression ratio. Thermal efficiency can be increased by late high-pressure injection of hydrogen. Direct injection timing is more crucial than hydrogen fraction for flame propagation. Increasing volumetric efficiency and turbulence intensity improve engine performance.