Comparative assessment of n-butanol addition in CTL on performance and exhaust emissions of a CI engine

Coal to liquid (CTL) is a diesel alternative fuel based on Fischer-Tropsch (FT) process, which has shown promising application value. Besides, as an oxygenated biofuel with high oxygen content and volatility, nbutanol can be blended with hydrocarbon fuels to improve engine performance. This study aims to investigate the effects of CTL/n-butanol blends on the performance of the compression-ignition (CI) engine, and to reveal the influence of combustion boundary conditions such as n-butanol blending ratio, the start of injection (SOI), and exhaust gas recirculation (EGR) on the combustion and emissions characteristics. The results show that blending n-butanol with CTL is beneficial to improve the fuel-gas mixture distribution in the cylinder, and the premixed combustion ratio (PCR) increases by 13.66% as the energy ratio of n-butanol increases to 30% (B30) compared with the pure CTL. CTL/n-butanol blends make particulate emission tend to be shifted towards nucleation mode and the particulate mass emission significantly reduced, especially the particulate mass of B30 reduce by 68.6%; meanwhile, the NOx emission shows an upward trend. Compared with n-butanol blended, adjusting the SOI impacts NOx emissions significantly, while its influence on the indicated thermal efficiency (ITE) and particulate emissions is relatively slight. Moreover, through the synergistic control of n-butanol addition and EGR, the tradeoff relationship between NOx and particles is mitigated.

Automated summary

CTL/n-butanol blends improve fuel-gas mixture distribution and increase premixed combustion ratio in the cylinder. Furthermore, through synergistic control of n-butanol addition and EGR, the tradeoff relationship between NOx and particles is mitigated.