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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.
Methanol has a cetane number of three and, consequently, extremely low
ignitability. Marine engines with spark ignition cannot exhibit mean effective
pressures as high as those of ordinary diesel engines because of the high rate of
pressure rise during ignition and they cannot 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
2. 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.
3.1 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.
STARTING TEST
4.l 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.
4.2 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.
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