2025 Sustainable Energy & Powertrains

Replacing fossil fuel by some e-fuels or bio-derived fuels is the pressing matters to suppress the increase in GHG emissions. Hydrogen, ammonia and lower alcohols are proposed as the fuels for internal combustion engines. Even though such fuels have already established mass production process and distribution network, their total supply is still far below than current demand of transport sector. Furthermore, such fuels are incompatible with the current and near-term fleets and supply infrastructures for each vehicle. Even if engines are fully modified to utilize such fuels with advanced combustion technologies like dual-fuel or RCCI, their market penetration may be slower than expectation, and their thermal efficiency could be lower than that of conventional CI engines using fossil fuels. This study was much inspired by REDIFUEL and HyFiT, and investigates into the co-optimization of fuel properties of synthetic fuels and CI engines to improve thermal efficiency (fuel economy) and exhaust emission characteristics of not only current fleets but also future anticipating high-efficiency MCCI engines. A single-cylinder heavy-duty CI metal engine (f135 x 140 mm), which can convert to the bottom-view transparent engine, was utilized for the engine experiments. Two types of fuels were tested. One was a higher alcohol, 1-octanol, blended with conventional fuel, while the others were several blends of n-paraffin and iso-paraffin fuels produced by Fischer-Tropsch synthesis with different properties, such as kinematic viscosity, distillation characteristics, and cetane number. The experimental results indicated that the fuels having a potential to improve thermal efficiency can also reduce heat loss by a kind of spatial insulation, maintaining a high temperature region away from the wall in the cylinder. It is suggested that the fuel properties of each component influenced this phenomenon, while average physical quantities, such as kinematic viscosity, could not capture it.