Engine NOx Out Mapping

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3.6.2 Urea Spray Pulse Length Setting Procedure

To determine a suitable spray pulse length the urea spray injector calibration chart as shown in figure 3.6.1 was used. Starting from 28 ms pulse length, the urea mass flow rate is found around 63.2 mgs. At engine speed of 1500 rpm and 6 bars BMEP, the exhaust mass flow rate was measured around 28.5 gramsseconds. Using this information, the potential ammonia gas produce at this setting was worked out to be around 695 ppm as shown in appendix 3.6.2. Repeating this procedure for various engine speeds from 1500 to 2500 rpm and load from 2 to 8 bar gives various exhaust mass flow rate ranging from 10 to 100 gramsseconds. As a result chart of the estimated required urea dosage against NOx was established as shown in figure 3.6.2 Figure 3.6.2 Chart showing estimated UreaAdBlue gs required against engine NOx out ppm

3.6.3 Engine NOx Out Mapping

Prior to selecting the appropriate spray dosage, the engine NOx out level mapping was also produced. This was achieved by running the engine at different Speed RPM and LoadBMEP bar. The engine mass flow rates were recorded manually as the engine speed varied from 1500 rpm to 2500 rpm and BMEP from 2 to 8 bars. The NOx levels were measured using the MEXA 1170Nx and

0.05 0.1

0.15 0.2

0.25 0.3

0.35 200 400 600 800 1000 ppm NOx re qui re d g s ur e a A d- bl ue s pr a y exhaust m 10 gs exhaust m 30 gs exhaust m 50 gs exhaust m 100 gs 50 EXSA 1500 analysers. Figure 3.6.3a and 3.6.3b provide a general engine mapping showing the engine NOx out and mass flow rate at various engine Speed RPM and load, BMEP bar. Figure 3.6.3a Engine NOx out based on Load BMEP bars, Speed RPM and EGR ON Figure 3.6.3b Exhaust Mass Flow gs based on Load, BMEP bars, Speed RPM and EGR ON. Based on the fact that the urea spray injector was for heavy duty applications, the lowest possible spray injector setting was utilized for this investigation. It was at 24 ms which is expected to produce about 550 ppm ammonia gas for the SCR reaction refer to calculation in appendix 3.6.2 In order to match the lowest urea pulse rate at 24 ms, the NOx out level must be in the range of 530 to 550 51 ppm. Therefore in the general NOx out mapping figure 3.6.3a the engine condition at 1800 rpm and BMEP 8 bars was appropriate at that time. Due to high fuel consumption at 1800 rpm and BMEP 8 bars, the EGR feature was switched off in order to increase the NOx level produced by the engine. The low engine speed is preferable based on lower fuel consumption which allows longer testing period with various urea spray and ammonia gas settings. Switching off the EGR also improved the NO-NO 2 ratio as detailed in section 3.8.2. Therefore another engine NOx out mapping was produce by running the engine at 1500 rpm with EGR off whilst varying the load BMEP from 2 to 8 bars with exhaust mass flow rate recorded. As a result the new engine mapping at 1500 rpm was produced as shown in figure 3.6.3c. From this engine mapping, the desirable engine condition was chosen as 1500 rpm and BMEP 6 bars with a mass flow rate of 28.5 gs. Figure 3.6.3c Exhaust Mass Flow gs based on Load, BMEP bars, Speed RPM and EGR OFF.

3.6.4 The Urea Spray Layout and Experimental Procedure