**3. Vegetable Oils**

Contemporary main diesel engines of sea-going ships are commonly supplied with heavy fuels oil (HFO). This very often also concerns auxiliary engines, especially electric generating sets. However, on many ships, the electric generating sets are still fed with marine diesel oil (MDO). Additionally, most diesel engines installed on small ships run on MDO.

Increasingly more attention is paid to alternative fuels, also called substitute, renewable, or unconventional fuels, because of the permanently increasing demand of marine diesel oil, their prices, and ecological requirements.

Unconventional fuels for supplying diesel engines are inter alia alcohol, ethanol, vegetable and mineral oils, fatty acid methyl esters, and diethyl ether [7]. In the research project planned by the author, supplying a ship with diesel engine only with a mixture of marine diesel oil (MDO) and rapeseed oil methyl ester (RME) was accounted for. It can be observed that some parameters of rape oil, their ester, and diesel oils show similar values. However, their density, kinematic viscosity, and flow temperature values differ from those of diesel oils. These data are listed in Table 2 [7].


**Table 2.** Comparison of some parameters of diesel oil, rape oil, and methyl ester of higher acid of rape oil (RME) [7].

As far as rape oils are concerned (interesting in the case of Poland), their density and viscosity is distinctly higher, which can make supplying diesel with them di fficult; however, their positive features are practically no sulphur content and their bio-degradation ability. The results of research on the application of only vegetable oil for supplying diesel engines (mainly in the automotive industry, and not on ships) show worse cylinder filling, worse supplying, and greater lengths of injected oil jets, associated with their large viscosity and density [7]. The expected phenomena associated with supplying diesel engines with rape oil are disturbing, namely, the often occurrence of clogging sprayer nozzles in the injector, and troubles with starting engines at low ambient temperature. There is also the seizing of precise pairs of injection pumps, and grea<sup>t</sup> susceptibility to the formation of carbon deposits on piston heads, ring grooves, valve, and valve seats.

Due to substantial di fficulties in applying rape oil only, as well as due to the limitation in using esters for running diesel engines, an alternative is to use mixtures of diesel oils and vegetable oil esters. In this way, it is expected to decrease the density and viscosity of the mixture to relative to those of a given ester. Tests on mechanical vehicles running on a mixture (20% rape oil/80% diesel oil) did not reveal any detrimental consequences [8].

Therefore, the author decided to carry out research on a marine diesel engine, to which the MDO/RME mixture containing up to 20% RME was fed.
