Properties and Performance of Levulinate Esters as Diesel Blend Components

The properties of ethyl (EL) and n-butyl levulinate (BL), two potential cellulose-derived diesel blend components, were assessed as both neat oxygenates and blends with diesel fuel. The samples tested were produced commercially from cellulose and alcohols but were not reagent-grade samples. They were relatively free of impurities, although EL contained some acidic compounds and both contained parts-per-million levels of calcium. Both esters exhibited a very low cetane number. The melting points of both esters were less than -60 degrees C. The water solubility of EL was 15.2 wt %, while that of BL was only 1.3 wt %. Blends of diesel fuel with EL were found to have an elevated cloud point, despite the extremely low melting point of this compound, because EL separates from diesel fuel as a separate liquid phase at low temperatures. This can be mitigated to some extent by including biodiesel in the blend. BL remained in solution and raised the diesel cloud point only when blended into -45 degrees C cloud point/15% aromatic no. 1 diesel fuel. Both esters were found to significantly increase diesel lubricity and conductivity. The esters were treated with the cetane-enhancing compound 2-ethyl hexyl nitrate and were tested as blends with diesel fuel in a 2008 model year Cummins ISB engine with the measurement of regulated pollutant emissions over the federal heavy duty diesel transient cycle. Fuel chemistry had no effect on tailpipe total hydrocarbons, carbon monoxide, or particulate matter for this diesel oxidation catalyst and particle filter equipped engine. The engine-out smoke number was reduced by 41.3% with a 10% blend of EL (EL10) and reduced by 55% with a blend of 20% BL (BL20). EL10 had no effect on emissions of nitrogen oxides (NOx), while BL20 increased NOx by 4.6%. Because of the poor solubility of EL in diesel fuel at low temperatures, its use as a diesel blend component will be technically challenging. The low cetane number of both esters can be addressed with cetane improver additives.