Combustion and Emission Performance from the Use of Acid-Catalysed Butanol Alcoholysis Derived Advanced Biofuel Blends in a Compression Ignition Engine

<div class="section abstract"><div class="htmlview paragraph">Low-carbon alternatives to diesel are needed to reduce the carbon intensity of the transport, agriculture, and off-grid power generation sectors, where compression ignition (CI) engines are commonly used. Acid-catalysed alcoholysis produces a potentially tailorable low-carbon advanced biofuel blend comprised of mixtures of an alkyl levulinate, a dialkyl ether, and the starting alcohol. In this study, model mixtures based on products expected from the use of <i>n</i>-butanol (butyl-based blends) as a starting alcohol, were blended with diesel and tested in a Yanmar L100V single-cylinder CI engine. Blends were formulated to meet the flash point, density, and kinematic viscosity limits of fuel standards for diesel, the 2022 version of BS 2869 (off-road). No changes to the engine set-up were made, hence testing the biofuel blends for their potential as “drop-in” fuels. Changes in engine performance and emissions were determined for a range of diesel/biofuel blends and compared to a pure diesel baseline. The ratio of butyl-based biofuel components ranged between 65 – 90 vol% <i>n</i>-butyl levulinate, 5 – 30 vol% di-<i>n</i>-butyl ether, and 5 – 10 vol% <i>n</i>-butanol. Formulating the blends to match physical property limits ensured that engine operation was not significantly influenced by changes in these selected properties. Emissions of CO, NO<sub>X</sub>, total hydrocarbons (THC), and PM<sub>2.5</sub> and particle number (PN) size distributions were measured. Compared to the baseline diesel, ignition delays were longer. The brake-specific fuel consumption of some butyl-based blends at high loads was within 5% of the diesel baseline. Most blends caused a less than 3% reduction in peak in-cylinder pressure at high loads, which contributed to maintaining engine efficiency. PM<sub>2.5</sub> and PN emissions were reduced significantly. CO and THC specific emissions increased relative to diesel for all blends, potentially due to their reduced derived cetane number. This however, resulted in increased premixed combustion favouring reductions in particulate emissions. The competing effects of changes in adiabatic flame temperatures and charge cooling effects, contributed to maintaining blend NO<sub>X</sub> emissions close to those of diesel. The results demonstrated the biofuel blends may have the potential to be low-carbon fuels used CI engines.</div></div>