2.2 Test Results and Consideration
To evaluate the influence of fuel properties on combustion and emissions, coefficients of correlation between them were calculated. The coefficients of correlation are shown in Table 4. In this table, coefficients of correlation between NOx and Pmax (Maximum cylinder pressure) are high values. And all coefficients of correlation between NOx concentrations at each load are not high values. Then, NOx concentration is influenced more strongly by combustion characteristic than by fuel property.
All the coefficients of correlation between soot concentrations at each load are high values, and the coefficients of correlation between soot and sulfur in fuel are also high values. Then, soot concentration is influenced strongly by sulfur in fuel. The relation between soot concentration and sulfur is shown in Fig.1. Soot concentration increases with an increase in sulfur content in fuel. Soot from MFO including 4% sulfur is approximately 4 times as high as that from MDF including 0.04% sulfur.1)
All the coefficients of correlation between HC concentrations at each load are high values. Then, HC concentration is influenced strongly by fuel. But it is unclear in this test what in fuel influences HC concentration.
3. WATER-EMULSIFIED FUEL
The use of emulsified fuel is an effective method to reduce NOx emission from marine diesel engine. However, there is an unclear point how other harmful exhaust emissions are influenced by the use of emulsified fuel. Therefore, influence of emulsified fuel on combustion and exhaust emissions was investigated by the burning test on a medium speed marine diesel engine with emulsified fuel.
3.1 Test Apparatus and Method
3.1.1 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.
3.1.2 Fuel used in test
MDF (Fuel A) shown in Table 2 was used in the test.
3.1.3 Measuring instrument
The measured composition of the exhaust gas and the kinds of the measuring instruments are shown in Table 3. Particulate Matter (PM) was measured by the method specified by ISO 8178.
3.1.4 Test method
The diesel engine was run at 25% load, 50% load, 75% load and 100% load of maximum continuous output with a propeller law using water-emulsified fuel, the characteristics of the diesel engine and the concentration of NOx, O2, CO2, CO, HC, N2O and PM in the exhaust gas from the engine were measured, and the effect of water-emulsified fuel on the harmful exhaust emissions was examined.
3.2 Test Results and Consideration
Effect of emulsified fuel on NOx concentration is shown in Fig.2. NOx concentration of emulsified fuel is lower than that of blank fuel at every load condition.
Effect of emulsified fuel on PM is shown in Fig.3. PM of emulsified fuel is considerably higher than that of blank fuel at low load condition, but it is not higher than that of blank fuel at high load condition.
Effects of emulsified fuel on CO and HC are shown in Figs.4, 5 respectively. CO and HC of emulsified fuel are higher than those of blank fuel at low load condition, but they are lower than those of blank fuel at high load condition, respectively.
Then, the use of emulsified fuel is extremely effective at high load condition to reduce NOx emission with no increase in other harmful exhaust emissions. But the use of it at low load condition causes the problem to increase PM, CO and HC.2)
