The potential of coal-to-liquid as an alternative fuel for diesel engines: A review

Abstract

Fuels made from coal-to-liquid (CTL) have the potential to partly take the place of petroleum-based fuels. CTL is also a significant way to promote the clean and effective use of coal while resolving the imbalance between the supply and demand of petroleum oil. CTL technology is crucial from a strategic perspective for coal-rich and oil-poor regions. Diesel fuel from direct coal liquefaction (DDCL) and diesel fuel from indirect coal liquefaction (DICL) are the two kinds of CTL fuels. This paper briefly introduces the development history and typical processes of DDCL and DICL, compares the physicochemical properties of DDCL and DICL with 0# diesel fuel, and shows that DDCL and DICL have lower sulfur and polycyclic aromatic hydrocarbon content, less carbon residue, better low-temperature fluidity, but lower lubricity. To analyze the differences and their causes and to suggest improvements in fuel quality, the results of DDCL and DICL engine experiments of different countries are compiled and compared with fossil diesel (FD) fuel in terms of power performance, efficiency & fuel economy, combustion characteristics and emission characteristics. The findings indicate that DICL has the lowest brake specific fuel consumption (BSFC) and the cleanest emissions, DDCL has the best dynamics and the highest premixed combustion ratio (PCR). The CTL technology development trend is highlighted to serve as a reference for the chemical liquefaction process.