Fig. 4 Comparison of combustion mode
3. Test apparatus and method
3.1 Test engine
The engine used in the operation is the medium speed engine of 280 mm in cylinder bore, and Table 1 shows its main specifications and standard specifications. A-heavy fuel oil on the market was used for the fuel.
3.2 Swirl generating device
The intake swirl for the air flow was given through the shroud valve. Fig. 5 shows the fitting position of the shroud valve obtained with the stationary flow test apparatus and the relationship between the swirl ratio and the intake air flow rate. The swirl can be changed without changing the cylinder head by fitting the shroud valve to either of two suction valves. In the test, the shroud position (S1+0) where the swirl ratio can be increased was obtained under the condition where the intake air flow rate is ensured as much as possible, and the test was carried out with the obtained swirl ratio at approximately 0.8.
3.3 Exhaust emission measurement instrument
NOx, CO2, CO, THC and O2 were measured using the content analyzer NEXA-9100D manufactured by Horiba Seisakusho. The exhaust smoke density was measured by the Bosch smoke meter, and expressed by the Bosch Unit (BSU).
4. Test results and consideration
4.1 Result of changing injection timing of test engine
Fig. 6 shows the test result of changing the injection timing at the rated output (266 kw/720 rpm) with the standard specifications (Table 1) of the test engine, showing that the NOx emission was reduced by retarding the injection timing, but the fuel consumption and the exhaust smoke were greatly degraded.
