This collaborative project between the University of Edinburgh, ISIS, the Diamond Light Source and the company Infineum UK, has used a range of techniques to perform the first structural investigation into the behaviour of biodiesel and one of its main components (methyl stearate) under high pressures.

The widespread use of biodiesel as a renewable fuel offers many potential advantages. It also presents challenges for modern diesel engines, particularly for those that involve high-pressure injection of fuel into the combustion chamber. At the elevated pressures used in such engines to reduce exhaust emissions, the biodiesel can crystallise, blocking the fuel filters and injection nozzles and causing engine failure.

The group used a high-pressure cell on the beamline PEARL at ISIS to study the crystallisation behaviour of methyl stearate using neutron powder diffraction, combined with complementary high-pressure experiments at the Diamond Light Source. The researchers observed four transitions between different structural phases, including one containing plate-like crystals.

The formation of these crystals could lead to potentially serious consequences if the process occurred in a fuel-injection system, thereby blocking the injection nozzle inside the engine. Future work is aimed at developing an enhanced understanding of the crystallisation processes of both methyl stearate and other major components of biodiesel under high pressures. 

“Yet again, the outstanding capabilities of the PEARL beamline have proved invaluable in tackling the fundamental science that underpins real-world, technological challenges." Professor Colin Pulham, University of Edinburgh.

Further Information

This manuscript​ forms part of a CrystEngComm themed issue on The effects of extreme conditions on molecular solids. Other works included in the themed issue also include high pressure studies of OP-ROY​ and  l-threonine; significant parts of both of these other studies were performed on the PEARL instrument.​