Fuel analysis:
Optimizing fuels
for state-of-the-art engines and injection systems
Filling Up with Synthetic Fuels?
Synthetic diesel fuels can reduce soot and hydrocarbon emissions from automobiles by about 40 percent, and carbon monoxide is reduced by as much as 90 percent. Tests conducted by Bosch researchers have revealed that all other emission levels remain about the same.
In this study, researchers fueled up a production diesel car with GTL, a synthetic fuel. GTL stands for Gas-to-Liquid, which denotes that natural gas has been made into diesel fuel by means of a synthesis process. And this product doesn’t contain any sulfur or aromatics!
It’s also possible to produce synthetic diesel fuel from biomass (Biomass-to-Liquid, BTL) or coal (Coal-to-Liquid, CTL) by using analogous methods. The raw material is converted into a synthesis gas – a mixture of H2 and CO – which in turn is converted into engine fuel by a process known as Fischer-Tropsch synthesis. The end products from those different source materials should be indistinguishable. A GTL road test has shown that the soot/nitrous oxide (NOx) trade-off is more favorable than with standard diesel fuel. This is a term that refers to the fact that when soot emissions are reduced by the engine management, NOx emissions are increased, and vice versa – which presents developers with a dilemma. The maximum benefit can be achieved by using a GTL fuel in combination with a particulate filter.
Long-term outlook
Researchers are investigating to what extent alternative fuels are compatible with existing engine designs, whether gasoline or diesel, what emissions they produce, and whether long-term effects occur, such as engine wear. If necessary, such fuels have to be additivated additionally, e.g. to improve lubricity and/or seizure protection.
It’s also possible to produce synthetic diesel fuel from biomass (Biomass-to-Liquid, BTL) or coal (Coal-to-Liquid, CTL) by using analogous methods. The raw material is converted into a synthesis gas – a mixture of H2 and CO – which in turn is converted into engine fuel by a process known as Fischer-Tropsch synthesis. The end products from those different source materials should be indistinguishable. A GTL road test has shown that the soot/nitrous oxide (NOx) trade-off is more favorable than with standard diesel fuel. This is a term that refers to the fact that when soot emissions are reduced by the engine management, NOx emissions are increased, and vice versa – which presents developers with a dilemma. The maximum benefit can be achieved by using a GTL fuel in combination with a particulate filter.
Long-term outlook
Researchers are investigating to what extent alternative fuels are compatible with existing engine designs, whether gasoline or diesel, what emissions they produce, and whether long-term effects occur, such as engine wear. If necessary, such fuels have to be additivated additionally, e.g. to improve lubricity and/or seizure protection.
During their activities the researchers include the full range of options, from bioethanol for gasoline engines to biodiesel and BTL. No doubt, bio-fuels will become increasingly important. Not only because of petroleum reserves are finite, but also because European legislators favor them. According to European guidelines, biogenic fuels will have to account for approximately six percent of total fuel consumption by 2010, and even further increases can be expected.
Bosch scientists are investigating what effects the new fuels will have on the materials, functions and service life of engine components. Biodiesel from rape oil, for instance, exhibits aging effects that make it more suitable for fleet vehicles, which are always on the move, than for a second family car that may sit in the garage for days on end.
Deposit formation
Depending on their composition, fuels may cause deposits to accumulate on internal component surfaces. Bosch scientist are investigating exactly where these deposits occur and how deleterious they can be. More precise study of the thermal and energetic properties of the synthetic fuels will have to be carried out in the future. This is because these properties play a major role in the complex injection systems.
And even state-of-the-art combustion methods can benefit from the use of synthetic fuels. In applications such as these, a long ignition delay combined with a high burn rate is desirable. This combination would, for instance, allow the HCCI method, which can be used only in a limited portion of the load range, to operate for a wider range.
