Study on the impact mechanism of ammonia energy fraction on in-cylinder combustion and pollutant generation under wide operation conditions of medium-speed diesel engines

• Published in: Fuel (Guildford) 2024-03, Vol.360, p.130617, Article 130617
• Main Authors: Qian, Yejian, Sun, Yu, Gong, Zhen, Meng, Shun, Wei, Xiaofei, Tang, Binbin, Wan, Juye
• Format: Article
• Language: English
• Subjects: Ammonia; Combustion; Dual-fuel engine; Energy ratio; NOx
• ISSN: 0016-2361; 1873-7153
• DOI: 10.1016/j.fuel.2023.130617

•Study on ammonia/diesel in-cylinder combustion based on medium-speed diesel engine.•The advance of diesel injection timing enhances the effect of diesel igniting ammonia in the cylinder.•The addition of ammonia in the combustion process decreases HC and CO emissions.•The NO2/NO ratio in the ammonia/diesel combustion products within the cylinder ranges from 10 % to 25 %, facilitating a rapid SCR reaction.•The majority of NOX are generated through the conversion process of ammonia in ammonia/diesel combustion mode. To expedite the utilization of ammonia in the domain of marine medium-speed diesel engines. The computational fluid dynamics (CFD) model combined with the ammonia/n-dodecane reaction mechanism were conducted to explore the impact mechanism of ammonia energy ratio (AER) and diesel injection timing on in-cylinder combustion and pollutant emission at low-mid-high loads of marine medium-speed diesel engines. Further, the formation laws of Thermal and Fuel nitrogen oxides (NOX) at various AER conditions were analyzed. At 10 % load, the rising AER advanced the CA50 by 57 % and increased the in-cylinder peak pressure by 3.5 % due to the enhanced premixed combustion stage. Whereas, at higher loads (50 % & 100 %), the effect of high specific heat capacity of ammonia played a crucial role in combustion progress with the increasing AER, which reduced the in-cylinder peak pressure by 1–3 %. The sensitivity of key combustion phases (CA10-CA90) to AER also gradually decreased with the rising loads because of the inhibited diffusion combustion stage. When the IT was 6°BTDC, the peak temperature in the cylinder decreased by 10 % at 10 % engine load; and the charge of excessive temperature in the cylinder was significantly reduced at 50 % and 100 % engine load. In terms of emission characteristics, HC and CO emission significantly reduced when AER was 45 %. And the proportion of Fuel NH3 in the fuel rose from 75.5 % to 91.4 % with the increasing AER. This means that the generation conditions of Thermal NOx were inhibited in the large proportion of ammonia-doped combustion conditions.