4. SELECTIVE CATALYTIC REDUCTION (SCR) SYSTEM
The improvement of the fuel consumption of the engine is effective to reduce the emission of CO2 which is the cause substance for the global warming, but the adjustment of the engine and the use of the emulsion fuel to reduce the NOx emission will worsen the consumption, resulting in the problem to increase the CO2 emission.
The use of the SCR system can greatly reduce the NOx emission, but also adjust the engine in a condition excellent in fuel consumption, and proves to be an effective method leading to the reduction of CO2. However, there is an unclear point how the other harmful exhaust emissions such as N2O are influenced by the use of the SCR system.
Thus, the harmful exhaust emissions such as N2O to be discharged from marine engines were examined using Marine Diesel Fuel (MDF) and two kinds of Marine Fuel Oil (MFO), and it was experimentally examined using tile SCR system how these harmful exhaust emissions were affected.
4.1 Test Apparatus and Method
4.1.1 Test engine
The test engine used in this test is the medium speed 4-cycle engine of 257 kW(350 PS)/420 rpm in maximum continuous output, and its principal particulars are shown in Table 1.
4.1.2 Fuel used in test
MDF and MFO shown in Table 5 were used in the test.
4.1.3 SCR system
The SCR system used in the test is of Selective Catalytic Reduction type with TiO2 - V2O5 for the catalyst and with 40% urea solution for the reducing agent, and its principal particulars are shown in Table 6. The typical reaction formula with this SCR system is as follows.
(NH2)2CO + H2O → 2NH3 + CO2
NO + NH3 + 1/4O2 → N2 + 3/2H2O
NO + NO2 + 2NH3 → 2N2 + 3H2O
4.1.4 Measuring instrument
The measured composition of the exhaust gas and the kinds of the measuring instruments are shown in Table 3.
4.1.5 Test method
The diesel engine was run at 50% load and 75% load of maximum continuous output with a propeller law using three kinds of fuel, the characteristics of the diesel engine and the concentration of NOx, O2, CO2, CO, HC, N2O in the exhaust gas from the engine were measured, and the effect of the fuel property on the harmful exhaust emissions such as N2O was examined. The temperature of the fuel was set to be approximately 100℃ at the inlet of the fuel pump in a case of MFO.
