Fig. 5 Comparison of in-cylinder pressure, in-cylinder temperature, injection pressure, injection period and heat release rate (50% engine load)
As for the trend of the change in the NOx concentration to the measuring time, the NOx concentration higher in the order of February, April and July was indicated both for the fuel A and the fuel C1. This is believed to be attributable to the effect of the absolute humidity. It is well known that, in the summer time when the absolute humidity is generally high, the NOx concentration is low, while is the winter time when the absolute humidity is low, the NOx concentration is high. Actually, the absolute humidity is lower in the order of February, April and July, and it is believed that the NOx concentration was higher in this order.
3.1.2 N2O
Fig. 6 shows the N2O concentration for each fuel. Fig. 7 shows the change in the N2O concentration to the measuring time with the fuel A and the fuel C1. It is shown from these results that the N2O value is low with MDF while N2O with MFO approximately 10 times as much as that of MDF is produced. With the fuel C1, N2O of approximately 1.5 times as high as that of the fuel C2 is produced though the nitrogen in the fuel is smaller. As for the generation of N2O, there are the paper1) that N2O is produced in the reaction of NOx, SOx and water at room temperature, and the paper2) that N2O is produced in the reaction of NOx with SOx in aqueous aerosol. The following reaction is proposed in the latter.
Fig. 6 Effect of difference in fuel property on N2O
Fig. 7 Change in N2O concentration to time of measurement
As show above, sulfur is greatly involved in the production of N2O, and it is considered the N2O value has been larger in the order of the fuel C1, the fuel C2 and the fuel A due to the effect of sulfur content in the fuel. Fig. 8 shows the N2O concentration to the sulfur in the fuel, showing the close relationship therebetween. In MFO, sulfur of at least 10 times that in MDF is contained in the fuel, and also in the fuel C1, the sulfur of approximately 1.8 times that in the fuel C2 is contained in the fuel, showing good correlation with the N2O concentration.
The trend of the change in the N2O concentration to the measuring time is similar to that in the NOx concentration. This is believed to be attributable to production of N2O in the chemical reaction of NOx, SOx and water in the exhaust gas. It is thus believed that the N2O concentration is lower as the NOx concentration is lower. Similar trend is shown with a case where the water emulsion fuel is used, and the N2O concentration was also reduced by reducing the NOx concentration3).
Fig. 8 N2O concentration to sulfur content in fuel
