3. 3. 5 Equivalent conversion management for the torsional angles of every cylinder.
The torsion angle of the crankshaft is measured as the result of composition of the torsion angles by the torque being generated in all cylinders. For carrying out the abnormal diagnosis, at first, this form of the composed torsion angles must be separated into the torsion angle being brought out by the torque of every cylinder and the effect of other cylinders must be excluded. The concrete measures are shown in below.
1. From the pre-measured gas pressure date in cylinders, calculate the torque form of gas pressure only in one cylinder.
2. Convert the calculated torque wave from into the torsion angle of each cylinder in consideration of the effective length of the crankshaft.
3. From the measured torsion angle form of the crankshaft, take away the torsion angle components being caused by the torque due to the inertia force of the reciprocating mass. And separate the torsion angle due to the torque being caused by the gas pressure in cylinders.
4. From the torsion angle form due to the gas pressure in cylinders, take away the torsion angles of ail other cylinders' excluding the said one.
5. If the individual torsion angle of each cylinder is multiplied the weighted coefficient due to the effective length of that cylinder, all cylinders can be comparable. Further, this operating method is called "The gas pressure in cylinder method".
3. 4 Consideration for applying to the actual ship
3. 4. 1 Torque conversion method of the torsion angle by the contribution rate.
In case of the analyzing method by the gas pressure system in cylinders as shown in the previous clause, it is necessary to calculate torsion angle from pre-measured gas pressure. Accordingly, in case of applying to the actual ship, this gas pressures in cylinder must be investigated for fitting to all load conditions of the engine. It is not realistic because of enormous work. Therefore, the method which is based on the pre-calculation of effect between crankshaft torsion angle and pressure in cylinder are accepted. The procedures are shown in below.
1. From the gas pressure data in cylinder, calculate the torque form by only the gas pressure in cylinder.
2. From the calculated torque form, calculate the torsion angle form of every cylinder under consideration of the effective length of the crankshaft.
3. The torsion angle form of each cylinder is composed for one cycle of the engine in firing order.
4. The contribution rate is considered as the torsion angle form of each cylinder divide by the compound wave from value.
5. The torsion angle components being brought out by the torque due to the inertia force of the reciprocating mass must be taken out from the torsion angle form of the measured crank shaft and separate the torsion anle being caused by the torque due to the gas pressure in cylinder.
6. Multiply the actually measured form by the contribution rate of each cylinder and then, separate the actually measured form to that of each cylinder.
7. By the revising factor of the contribution rate being obtained in advance from the actually measured gas pressure in cylinder, each contribution rate must be revised.
8. If the individual tortion angle of each cylinder is multiplied to the weighted coefficient due to the effective length of that cylinder, all cylinders can be comparable on the same level.
3. 4. 2 Contribution rate revised coefficient
The above-mentioned contribution rate is dealt with as the constant, irrespective of the load change. However, it is confirmed that the contribution rate is actually changed in proportion to the increase or the decrease of the load and its effect becomes larger to the cylinder as near as the output end. Thus, the contribution rate revised coefficients calculated by the following method and is revised in proportion to the load ratio.
1. From the pre-measured gas pressures in the cylinder over 4 points on the propeller characteristics, the contribution rate is calculated in each load and each cylinder.
2. Find the ratio of the contribution rate of each cylinder and each load against these of at 100% load and make it as the revised coefficient.
3. By means of the minimum square-law, the relations between the revised coefficient and the load are replaced into the curve of secondary degree.
4. Find out the contribution rate revised coefficient from above curve of secondary degree.
