In order to deeply investigate and improve the complete path from biofuel production to combustion, the cluster of excellence “Tailor-Made Fuels from Biomass” was installed at RWTH Aachen University in 2007. Recently, new pathways have been discovered to synthesize octanol [1] and di-n-butylether (DNBE). These molecules are identical in the number of included hydrogen, oxygen and carbon atoms, but differ in the molecular structure: for octanol, the oxygen atom is at the end of the molecule, whereas for DNBE it is located in the middle.
In this paper the utilization of octanol and DNBE in a state-of-the-art single cylinder diesel research engine will be discussed. The major interest has been on engine emissions (NOx, PM, HC, CO, noise) compared to conventional diesel fuel. Soot emissions can almost be avoided completely with octanol, but due to its longer ignition delay (cetane number (CN) ∼ 40), an increase of HC- and CO-emissions about 20% is observed at part load compared to diesel fuel. Even though DNBE has a CN ∼ 100, the combustion can be considered to be almost soot free even at Euro 6 NOx-levels at high part load. In contrast to octanol, due to the fast ignition of DNBE, over-leaning at low load operation can be prevented.
To gain a better understanding of this phenomenon, both fuels have been characterized at engine relevant boundary conditions inside the continuously scavenged high-pressure chamber test bench at RWTH Aachen University. The results show that DNBE provides a significantly decreased ignition delay and lift-off in comparison to octanol.
To provide deeper insight into the spray and mixture formation processes, numerical simulations of the spray vessel experiments are undertaken. The physical properties of DNBE and octanol are integrated into the data base of an in-house CFD code. Spray simulations show good agreement to experimental data concerning liquid and gaseous penetration length and spray cone angle. The numerical results allow for closer analysis of the fuel mixture fraction at the experimentally observed ignition location and thus help to explain the differences in the ignition and the similar sooting behavior.