Optimization of Diesel Combustion and Emissions with Newly Derived Biogenic Alcohols 2013-01-2690

Modern biofuels offer the potential to decrease engine out emissions while at the same time contributing to a reduction of greenhouse gases produced from individual mobility. In order to deeply investigate and improve the complete path from biofuel production to combustion, in 2007 the cluster of excellence “Tailor-Made Fuels from Biomass” was installed at RWTH Aachen University. Since then, a whole variety of possible fuel candidates have been identified and investigated. In particular oxygenated fuels (e.g. alcohols, furans) have proven to be beneficial regarding the particulate matter (PM)/ NOx trade-off [1, 2, 3] in diesel-type combustion. Alcohols that provide a longer ignition delay than diesel might behave even better with regard to this trade-off due to higher homogenization of the mixture. Recent studies carried out within the Cluster of Excellence have discovered new pathways to derive 1-octanol from biomass [4], which features a derived cetane number (DCN) of 39. In combination with its boiling point within the range of diesel, it is very suitable for operation in compression ignition (CI) engines.

In the first part of this paper, a review of the synthetic pathway to 1-octanol via platform chemicals derived from a lingocellulosic feedstock is presented. A multifunctional catalytic system has been developed providing access to 1-octanol based on furfural and acetone as cheap and readily available starting materials [4]. All transformation steps can be integrated into a one-pot reaction cascade without the need for intermediate work-up or isolation. Together with previous work on the fractionation of lignocellulose [5] coupled with the generation of furfural [6], this provides a proprietary direct route from wooden biomass to 1-octanol.

In the second part of this publication, the utilization of 1-octanol in a state-of-the-art single cylinder diesel research engine will be discussed. The results will be compared to those with long chained alcohol 1-decanol and diesel. During these tests, the major interest has been on engine emissions (NOx, PM, HC, CO, combustion noise). It could be proven that with 1-octanol the PM-emissions can be reduced by about factor 20 compared to diesel fuel and even further reduce PM emissions compared to 1-decanol at same NOx-emissions. However, the slightly lower cetane number causes minor over-leaning effects in particular at lowest load. Thus, the HC- and CO- as well as combustion noise emissions exceed those of diesel combustion at low load operation.