Investigation on combustion characteristics and gas emissions of a high-pressure direct-injection natural gas engine at different combustion modes

• Published in: Energy conversion and management 2023-02, Vol.277, p.116617, Article 116617
• Main Authors: Chen, Guisheng, Wei, Feng, Zhang, Kaiqi, Xiao, Renxin, Wang, Zhenjiang, Yang, Shun
• Format: Article
• Language: English
• Subjects: Gas emissions; High-pressure direct-injection; Mixing-limited combustion; Natural gas pre-injection; Slightly premixed combustion
• ISSN: 0196-8904; 1879-2227
• DOI: 10.1016/j.enconman.2022.116617

•The diesel/natural gas dual direct injection model is adopted for calculation.•The effects of injection parameters in natural pre-injection mode are investigated.•Features of mixing-limited mode are compared to those of slightly premixed mode.•Mixing-limited mode has potential to improve thermal efficiency and carbon monoxide. In the present study, the potential of natural gas pre-injection, mixing-limited combustion, and slightly premixed combustion modes were evaluated to achieve high thermal efficiency and low nitrogen oxides and carbon monoxide emissions. To this end, a dual direct injection model was established to perform numerical simulations. The obtained results revealed that in the natural gas pre-injection mode, the optimized natural gas pre-injection proportion and injection interval between the end of natural gas pre-injection and the start of diesel injection can significantly reduce carbon monoxide emissions and improve indicated thermal efficiency with a slight increase in nitrogen oxides. In the mixing-limited combustion mode, combustion phasing and indicated thermal efficiency are not sensitive to the variations of the injection interval between diesel and natural gas. Moreover, a larger injection interval between diesel and natural gas is beneficial to reduce carbon monoxide. In the slightly premixed combustion mode, as the injection interval between diesel and natural gas decreases, combustion phasing delays, carbon monoxide emissions reduce, and nitrogen oxides emissions increase first and then decrease. Advancing the start of natural gas injection increases maximum pressure rise rate and nitrogen oxides in both natural gas mixing-limited combustion and slightly premixed combustion modes but decreases carbon monoxide dramatically. The natural gas mixing-limited combustion mode has more potential to meet carbon monoxide limits imposed by the Euro VII standard with no need for extra after-treatment devices while improving thermal efficiency.