Two-stroke cycle diesel engine mounted on a car carrier (19,000dwt) was used as a test engine in this study. The specification of this engine is 8-cylinder and 16,320kW in output. The data collection was started immediately after the manufacture of the engine, and the data obtained in one and a half years after the ship went into service (the running time of the engine: 7800 hours). Fig. 1 is a section of the engine, a vibration sensor is mounted on the part indicated by an arrow in the figure, and the radiant sound was recorded at the position away from the vibration sensor mounting position by 5cm in the vertical direction. And, at the same time, the synchronous pulse signal to measure the synchronization of the data on the vibration and the radiant sound with the rotation of the engine was also taped. The above-mentioned sensor was mounted on No. 1 cylinder, and the cylinder was subjected to the examination. The collected data on the vibration and radiant sound was frequency-analyzed by an FFT analyzer. More specifically, the time of one cycle was divided into 120 sections, and frequency-analyzed in the measurement range of 20kHz.
Fig. 1 Test engine
The time relationship between the synchronous pulse signal generated for each cycle of the engine and the opening/closing condition of each cylinder valve is shown in the valve timing in Fig. 2. The figures at the left end show the number of each cylinder, and the completely black-covered parts E.V. on each line show the opening condition of the exhaust valve. The ignition order of the cylinders is 1-8-3-4-7-2-5-6.
E.V.: Exhaust Valve o: open c: close T: Top Dead Center B: Bottom Dead Center
Fig. 2 Valve timing
3. Three-dimensional indication of sound level and vibration level
Figs. 3 to 6 show the spectrum of the radiant sound and the vibration in the shop trial run of the engine in a three-dimensional manner. Here, the spectrum immediately after the manufacture of the engine is examined, and its temporal transition is also evaluated and examined. On the basis of the data of one cycle of the engine (1 rotation of the crank shaft) obtained through the frequency analysis, the three-dimensional figures of the sound pressure level and the vibration level in the light-and-shade pattern with the frequency (100-20kHz) on the Y-axis and with the crank shaft angle (0-360°) on the X-axis, the figure of the valve timing is also indicated on the upper part of the three-dimensional figure to explain both the behaviors of the piston and the valve of each cylinder and the temporal change in the three-dimensional figure. The scale of the sound pressure level or the vibration level is indicated in the pattern below the three-dimensional figure.
The three-dimensional figures of the radiant sound and the vibration in three hours after the shop trial run was started, are shown in Fig. 3 and Fig. 4, respectively. The result (Fig. 3) of the radiant sound shows thick lines in the Y-axis direction in the ranges of A (0-40°), B(80-120°), and C (210-250°). When reviewed together with the figure of the valve timing above, it is proved that these agree with that combustion in No. 1, No. 3 and No. 2 cylinders. Therefore, it is concluded that they are attributable to the combustion. On the other hand, when reviewed from the result (Fig. 4) of the vibration, a completely different pattern is shown from that in Fig. 3.
