Published on Apr 02, 2024
Energetic research on methanol-fueled automobile engines has been forwarded from the viewpoints of low environmental pollution and the use of alternate fuel since the oil crisis, and they are now being tested on vehicles in various countries in the world.
Various technical issues have already been solved or the prospect is bright for them. It can be said that this type of engine is very close to completion at present. On the other hand, it is an actual situation in the marine engine field that the research on this type of engine has hardly been tested so far, since it has seldom been evaluated from the viewpoint of environmental pollution control because it is used at sea and the idea to use methanol on marine engines is not established yet.
However, IMO (International Maritime Organization) is now investigating to include exhaust gas from ships in the objects to be controlled from the viewpoint of environmental protection on a worldwide scale that has been loudly emphasized recently. In case clean methanol is used as fuel, work for handling complicated machines such as centrifuges for heavy fuel oil and for treating sludge discharged from them can be avoided, and further it can be expected to lessen frequent engine maintenance work.
It has therefore been strongly desired to use methanol on marine diesel engines from mainly the viewpoint of pursuing economy. Though knowledge which has been gained with automobile engines can be used in principle, many subjects to be solved still remain, since marine diesel engines have large bores and mean effective pressures of more than two times as much, their operating conditions are extremely severe and they need high reliability and durability in comparison with automobile engines.
Methanol has a cetane number of three and, consequently, extremely low ignitability. Marine engines with spark ignition can not exhibit mean effective pressures as high as those of ordinary diesel engines because of the high rate of pressure rise during ignition and they can not permit misfiring because of the large volume of their exhaust systems. The dual fuel injection system which has actual service results on large-sized gas engines has therefore been selected as the ignition system for this research. Since methanol is not only corrosive but also insufficient in lubricating ability, elemental research has been needed to solve these issues
A single cylinder, four-stroke, direct-injection type diesel engine having a cylinder bore of 250mm has been modified so as to be suitable for this experiment. The rated speed of this experimental engine has been set lower than that of the original type so that the results of this research can be utilized as widely as possible.
The combustion system of the experimental engine is of a dual fuel injection type such that the main fuel injection valve (methanol) is located at the centre of the combustion chamber and atomized fuel from this valve is ignited by the pilot oil injection from the secondary injection valve (oil) located on the cylinder head near the periphery of the combustion space.
This system has been adopted from the reasons that it has the high stability of ignition, good low load performance and high reliability, and that it serves as a measure to prevent corrosion, since combustion deposits made by pilot oil injection cover the inside surface of the combustion chamber. The methanol injection pump is of a forced lubrication type to prevent lubrication troubles.
Since methanol is highly volatile, the auxiliary equipment of the methanol system such as the fuel tank, strainer, supply pump and valves have been installed in an enclosed chamber (a fuel supply unit) as shown in Fig.2. A fan and a gas detector have been installed to sufficiently ventilate the inside of the unit for safety. Pipe joints are also of special structure to prevent fuel leakage.
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