In the previous study, the experiments have been carried out using high viscosity fuels up to 1000 cSt (@50°C) on a medium speed diesel engine and it has been reported that combustion characteristics such as ignition delay and smoke at low load deteriorate according to the increase of viscosity.
Since the fuel used above mentioned experiments has been prepared by the same diluent and base oil with different mixing ratio, it can be said that the different combustion characteristics along with the viscosity is due to the difference of their mixing ratio i.e. the influence of diluent and base oil.
In the actual fuel market, however, fuels are made using various kinds of diluent, and it is supposed that the combustion characteristics will vary owing to the properties of diluent and mixing ratio even on the same viscosity.
This paper describes the results of experiments using the fuel of 180 and 380 cSt (@50°C) prepared by different diluents mixed with vaccume residue as base oil. Pure diluents are also tested in order to compare with high viscosity fuel.
As a result, it is known that fuel quality does not depend on viscosity and diluent acts an important role in the combustion characteristics especially on ignition delay.
Ignition delay correlates well with CCAI, UOP-K and corresponds closely to the mixing ratio as well.
The limit of stable operation due to long ignition delay is also discussed in the paper.
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