The effect of the SCR system on the harmful exhaust emissions such as N2O was examined by measuring the exhaust gas concentration when the reducing agent was poured in the SCR system at the outlet of the SCR system, and when no reducing agent was poured.
4.2 Test Results and Consideration
Fig.6 shows the example of measurement, and it is understood that NOx and N20 are greatly reduced by using the SCR system. It is well known that N2O is reacted in the extinguishing reaction in addition to the generating reaction with NOx.3)
H + N2O → N2 + OH
O + N2O → N2 + O2→ NO+NO
It is considered that the N2O concentration is reduced as shown in Fig.6 as the result that the decomposing reaction of N2O by the hydrogen radical (H) and the oxygen radical (O) to be generated in the process of the NOx-removal reaction exceeds the generating reaction of N2O by NOx.
HC is reduced by using the SCR system. It is considered that HC is reduced by the oxidizing reaction of HC and by consumption of HC as the reducing agent of NOx. On the change in CO concentration by using the SCR system, no remarkable trend was found.
As for the effect of fuel property on N2O emission, it seems that N2O concentration is influenced by sulfur in the fuel. Fig.7 shows the N2O concentration to sulfur content in the fuel, showing the close relationship there between.4)
5. ELECTRONICALLY CONTROLLED HYDRAULIC SYSTEM FOR FUEL INJECTION AND INLET/EXHAUST VALVE ACTUATION
The electronically controlled hydraulic system for fuel injection and inlet/exhaust valve actuation on the diesel engine is an effective method to reduce harmful exhaust emissions and fuel consumption because of achievement of optimum engine operation in response to changing conditions including engine loads and fuel properties.
Now, we have mounted the electronically controlled hydraulic system for fuel injection and inlet/exhaust valve actuation on the 3-cylinder engine. And we are carring out operation test of the engine. The outline of the electronically controlled system is reported below.
5.1 Electronically Controlled Hydraulic System for Fuel Injection and Inlet/Exhaust Valve Actuation
The test engine used in this test is the medium speed 4-cycle engine(3 cylinders) of 257 kW (350 PS)/420 rpm in maximum continuous output, and its system diagram are shown in Table 1.
The outline of electronically controlled hydraulic system for fuel injection and inlet/exhaust valve actuation is shown in Fig.8. This system is organized by the power supply unit, the operation oil pressure generation unit, tile control unit with micro-computer, the cylinder units with solenoid valves. And it enables to control each fuel injection timing and each valve opening/closing timing independently.
On this system for fuel injection, the Bosch-type injection pump is driven by the cylinder unit with hydraulic pressure instead of the conventional camshaft. Then, even if low engine rotation, high fuel injection pressure can be obtained. The volume of fuel injected was adjusted by the conventional governor. Moreover, the fuel injection timing can be changed by 0.5 degree of crank angle freely.
On the system for inlet/exhaust valve actuation, the valve is driven by the cylinder unit with hydraulic pressure instead of the conventional camshaft too. Then, even if low engine rotation, high speed of the valve actuation can be obtained. Moreover, the valve opening/closing timing can be changed by 0.5 degree of crank angle freely.
This electronically controlled hydraulic system for fuel injection and inlet/exhaust valve actuation operates on not only one cylinder but also all three cylinders. It is expects that flexibility in engine operation optimizes fuel consumption and exhaust gas emissions throughout the whole engine load range.
Now, we have mounted this system on the 3-cylinder engine, have checked the functions of this system, and have gotten favorable engine operation test. This research is carried out in cooperation with NABCO Ltd.. The authors wish to express their gratitude for the assistance of NABCO Ltd..
6. CONCLUSION
6.1 Fuel Property on Harmful Exhaust Emissions
NOx concentration is influenced more strongly by combustion characteristic than by fuel property.
Soot concentration is influenced strongly by sulfur in fuel.
