The lifecycle analysis for the fuel dimethyl ether (DME) has shown fantastic results and Volvo’s developers have succeeded in utilising it efficiently with minimal emissions. There was however one problem remaining to be solved; the fuel forms a coating in the fuel system, blocking fuel filters. RISE, working in collaboration with Volvo, has now found a solution.
DME can be manufactured in a number of ways, including from the gasification of black liquor, a byproduct of paper pulp manufacturing. Automotive manufacturer Volvo has come a long way in adapting its diesel engines for using DME.
“This fuel works fantastically well in Volvo’s diesel engines. It also has a high cetane number, indicating that it is highly combustible under compression, which is an important parameter,” says Anders Lorén, project manager at RISE.
Not only that, a life-cycle analysis of DME demonstrated extremely positive results from an environmental standpoint, with such low particle emissions that a particle filter is no longer required.
In adapting their diesel engine, Volvo has made a number of changes to the fuel system and invested many hours on the test track and with customers.
The problem, however, proved to be persistent; after a few dozen miles of operation, the fuel system became coated and the filters were blocked. The initial hypothesis was that, for some reason, the fuel was reacting to form clumps;
however, an experiment at RISE to simulate high pressure, high temperature engine conditions demonstrated that this was not in fact the case.
“Instead, we were able to confirm that the interaction of engine oil with fuel was creating a coating. We then understood that we needed to develop a new engine oil,” explains Anders Lorén.
The engine oil contained a number of functional chemicals; including detergent to prevent cakes of soot. viscosity modifiers to create a thin and easy-to-start oil, antioxidants and antiwear substances.
“These are chemicals that create a good chemistry and improve the properties of the oil; however, it proved impossible to transfer the same chemistry from diesel to DME,” says Anders Lorén.
In collaboration with Volvo and the manufacturers of the chemical additives, RISE has now developed new engine oil recipes. The most promising of these have been tested in a test rig at Volvo in Malmö, as well as in vehicles in traffic in Gothenburg during the summer. The reaction has been positive and now only the final control measurements remain.