02-07-2014, 12:05 PM
Methanol Fueled Marine Diesel
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ABSTRACT
Nowadays concerns about methanol have increased from the viewpoints of environmental protection and versatility of fuels at a global scale. 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. Desire for saving of maintenance cost and labour prevails as well as the environmental problems in the field of marine engines. From these motives scientists have carried out research and development of a methanol fueled marine diesel engine which is quite different from automobile engines in the size, main particulars, working condition and durability. Although scientists have made a great use of invaluable knowledge from automotive technology, some special studies were necessary due to these differences. Ignition method is a typical one. Dual fuel injection system was tried for trouble-free ignition of methanol fuel. This system is thought to be the most favourable ignition method for marine diesel engines which have to withstand quick load change and accept no misfiring.
INTRODUCTION
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
[b]EXPERIMENTAL ENGINE
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. Table 1 and Fig.1 show the principal particulars of the experimental engine and the schematic drawing
OPERATION TEST UNDER NORMAL CONDITION
Under the full load condition of the above mentioned experimental engine (mean effective pressure Pme: 16.13kgf/cm), influence on engine performance, the contamination condition of engine inside and lubricating oil, and the properties of exhaust gas have been investigated by changing the specifications of the pilot oil injection nozzle, main fuel injection nozzle and main fuel injection pump, fuel injection timing and the quantity of pilot oil.
Influence of Pilot Oil Injection Nozzle
The effect of the pilot oil injection nozzle has been confirmed by changing the number and diameter of nozzle holes and the direction of injection in the range shown in Fig.4. As a result, the one-hole nozzle is the best in terms of fuel consumption, the stability of cylinder pressure and the reduction in the quantity of pilot oil
Influence of Methanol Injection Nozzle
Engine performance has been confirmed using methanol injection nozzles of which the numbers of nozzle holes are 8, 9, 10 and 12, and nozzle hole diameters have been selected in the range from 0.39mm to 0.48mm (90% to 200% of the nozzle area of the injection nozzle for burning only oil).As a result, it has turned out that, in case of the experimental engine, the injection nozzle which has ten nozzle holes of 0.46mm in diameter, i.e.150% of the nozzle area of the injection nozzle for burning only oil, shows the best fuel consumption. Fig.7 shows engine performance against the number of injection nozzle holes using intake air pressure as a parameter when using injection nozzles of which areas have been kept constant (130% of the nozzle area of the injection nozzle for burning only oil) and the number of nozzle holes has been 8, 10 and 12.
Though the 8-hole nozzle shows the specific fuel consumption on almost the same level as that for the 10-hole nozzle, the former shows better performance, since both Pmax and exhaust temperature are lower. However, it is considered in this case that thermal loads on the combustion chamber components become high due to the longer fuel spray travel by about 7% than that for gas oil
Influence of Injection Timing
As seen in this figure, the engine performance becomes better in case where pilot oil is injected earlier by two degrees than methanol. Though the test where pilot oil is injected later than methanol has also been carried out, combustion has not stabilized and continuous running has been difficult. Another test has also been carried out, where the relative difference in injection timing between methanol and pilot oil has been fixed and the timing for both fuels has been advanced in parallel. However it has turned out that the improvement in fuel consumption is small.
Test Method
The stable combustion of dual fuel engines under normal operation can be ensured by pilot oil of several percent of total fuel which is injected under full load condition. However, a considerably large quantity of fuel is needed when starting engines, since accelerating torque is necessary in addition to normal running torque. For this reason, starting tests have been carried out under the following conditions.
a) Constant quantity of methanol (full load) and varying quantity of pilot oil
b) Constant quantity of pilot oil and varying quantity of methanol
c) Operation on only pilot oil
d) Starting on pilot oil and injection of methanol after that
e) Constant quantity of methanol (50%) and varying quantity of pilot oil
For all conditions except e), cold conditions of intake air temperature ts=191C , cooling water temperature twt=191C , lubricating oil temperature to=01C and liner temperature tL=201C have been adopted. For a part of e) condition, warm conditions of tst=301C , tw=58 C , to=50 t and tL=391C have been adopted
Test Results
Fig.15 shows the summaries of test results taking the quantity of pilot oil on the abscissa and that of methanol on the ordinate.
Mark shows that no ignition has been detected. Figure show that, though ignition has been detected, it has not been continued and torque has not been generated. Figure show that ignition has been detected and continued stably and engine speed has risen up to its set speed. Suffixes show test numbers
CONCLUSION
Tests have been carried out under static and dynamic conditions in order to grasp engine performance when methanol is applied to marine diesel engines. As a result, it has turned out that the performance of a methano1/oil burning engine can be improved near to the performance level of an oil burning engine by
1. Optimizing the fuel injection system and the combustion chamber geometry
2. Adapting the fuel regulating system and the intake air system of the former