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It has been a basic design criterion that two-stroke low-speed diesel engines should be able to burn the lowest and cheapest qualities of fuel oils that are commercially available. For this reason, extreme fuel qualities, right from their appearance on the market, always have been used in such engines. Developments in the mineral oil industry, well described in numerous articles, have caused an increasing volume of fuel oil to be used in the lower end of the quality scale. Also, a more diversified market pattern has led to the frequent occurrence of such extreme fuels in an increasing number of bunkering ports of the world.
In consequence, it was only natural that a comprehensive test program was initiated a few years ago by the engine industry to meet the challenge raised by this forecasted development. Several samples of fuels were secured from various oil companies. These samples, which came from all over the world for testing, were evaluated by the supplying oil companies as representative of the qualities predicted by the forecasts and, as such, were representative for the fuels on the market in the eighties.
Simultaneously, the engine industry established an increased contact with the manufacturers of equipment for on-board fuel treatment, that is, makers of fuel oil centrifuges, filters, and homogenizers as well as makers of pumps, heat exchangers, etc. Also, the systematic accumulation of service results from these ships in service, which according to experience were originally expected to use larger volumes of such marginal fuel qualities, was intensified. The conclusion of the combustion research was that all these so-called extreme fuel qualities could be used in most larger marine diesel engines as has been the case with the traditional heavy fuels.
The same result was concluded by the plants in service that were especially followed in the fuel research program. However, for the ships in service, it also could be concluded that it was of extreme importance that the on-board fuel treatment was adequate. This paper will describe further the just mentioned tests and service results as well as engine design steps taken dictated by, among other reasons, the fuel quality development. Also, tests with coal derivatives, fuel-water emulsions, as well as fuel oil specification tendencies will be discussed. The practical aspects of using extremely heavy and poor fuel qualities in plants in service will be discussed, especially such issues as fuel oil pretreatment, that is, preheating and cleaning. In particular, installation and service aspects will be enlarged upon, with a look forward to a further decline of fuel qualities.
fuel quality, fuel consumption, fuel treatment on board, low-speed diesels, combusion chamber components
Manager, Marine Installations, MAN—B&W Diesel A/S, Copenhagen,