Urea sprays studies: Ammonia levels upstream of SCR bricks. Ammonia gas studies: upstream measurements. 1 and 4 SCR bricks

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4.1.3 Urea spray studies: Deduced value.

To deduce NH 3 , and NO 2 , it was necessary to use the difference between the potential SUM upstream and the SUM downstream in this case. Therefore, using the following equation Pot SUM upstream – SUM downstream = [NH 3 + NO + NO 2 ] consumption in the catalyst. The implication of this is the assumption that SUM downstream is the true measurement of the ammonia gas plus the NOx with no droplets or HNCO passing through the catalyst. This assumption may not be true for the 1 SCR, where ammonia in droplet form or possibly as HNCO at the catalyst exit is unaccounted for. But, it should however be true for the 4 SCR bricks case. It is again reasonable to assume that these species can only be consumed if they react with one another, and that they react on a mol NH 3 per mol NOx basis. It also neglects non mol to mol reactions and ammonia oxidation. There may be also additional reactions with urea by products that are neglected. Therefore, ½ [NH 3 + NO + NO 2 ] consumed = NH 3 consumed = NOx consumed NO consumed can be found directly from [NO upstream – NO downstream] Hence, NO 2 consumed = [NOx consumed – NO consumed]

4.1.4 Urea sprays studies: Ammonia levels upstream of SCR bricks.

In getting the ammonia levels, the calibrated spray pulse length setting and the knowledge of the exhaust mass flow rate can be used to calculate the potential ammonia level in ppm at location upstream of the SCR. This can be compared with the deduced value obtained from [SUM-NOx]. The difference between the levels would give an indication of how many of the droplets have released their ammonia between the spray injection point and the gas analysis measurement point upstream of the SCR. The 1 SCR and 4 SCR cases give remarkably different amounts of ammonia released from the droplets upstream of the SCR. It is not immediately apparent why this should happen, as the temperatures in the two experiments were very much similar and the main difference was the SCR resistance to the flow. This is further discussed in section 4.5.1. 82

4.1.5 Measurement with Urea Spray and 1 SCR brick.

Table 4.1.5 summarizes the test results associated with urea spray and 1 SCR brick. Potential ammonia release from the urea spray was also calculated. The NH 3 reading upstream from MEXA was recorded and clearly does not represent the correct NH 3 values. The SUM readings previously introduced in section 4.1.1 have been recorded from several set SUM readings and the average values were used in this table compiled from data shown in appendix 4.1.5b. Upstream of SCR, direct measurement of SUM, NO, NOx and NH 3 were tabulated in the table. For downstream measurements, only SUM, NO and NH 3 were obtained directly from MEXA. Table 4.1.5 Summary of Result: Urea Spray with 1 SCR. all measurements in ppm Results for urea spray 1 SCR Temp upstream 573 K Temp downstream 574 K O2 upstream

9.70 O2 downstream

7.90 1 SCR Spray pulse length ms -- Description 24 26 28 30 32 34 36 Refn Guide Apdx Potential up 1SCR Potential NH3 552 614 696 818 888 960 1042 calc A 3.6.2 Potential up 1SCR Potential SUM 505 1057 1119 1201 1323 1393 1465 1547 Potnh3 +nox B MEXA up 1SCR SUM 550 645 680 700 723 734 754 761 avg sum C 4.1.5b MEXA, Spray off up 1SCR NO 196 196 196 196 196 196 196 196 070708a D 4.1.5 MEXA, Spray off up 1SCR NOx 505 505 505 505 505 505 505 505 090708c E 4.1.5 Calculated up 1SCR NO2 309 309 309 309 309 309 309 309 nox-no F MEXA Reading up 1SCR NH3 21 210 250 290 310 320 345 385 090708c G 4.1.5 Deduced ammonia up 1SCR SUM-NOx 45 140 175 195 218 229 249 256 sum-nox C-E=H MEXA dw 1SCR SUMexcludes drops 539 495 564 607 661 732 797 863 avg sum I 4.1.5b MEXA dw 1SCR NO 200 137 139 139 140 140 140 140 070708b J 4.1.5 MEXA Reading dw 1SCR NH3 21 222 312 395 450 513 614 680 090708b K 4.1.5 NH3 + NO2 dw 1SCR SUM-NO 339 358 425 468 521 592 657 723 calc I-J=L NH3 + NOx consumed across 1 SCR Potential SUM- SUM -34 562 555 594 662 661 668 684 calc B-I=M Value too large because downstream sum was too small as it excluded drops Note: Plotted against potential ammonia supplied 1 SCR spray Pot NH3 up 552 614 696 818 888 960 1042 A up - down, 1SCR SUM-SUM 1SCR -34 562 555 594 662 661 668 684 M 1SCR spray NOx or NH3 consumed -17 281 278 297 331 331 334 342 M2=N 1SCR spray NO consumed -4 59 57 57 56 56 56 56 D-J=O 1SCR spray NO2 consumed -13 222 221 240 275 275 278 286 N-O =P concentration table pot NH3 up 552 614 696 818 888 960 1042 A Deduced ammonia upstream 1SCR SUM-NOx 45 140 175 195 218 229 249 256 H NH3 17 271 337 399 487 558 626 700 A-N NOx 522 224 228 208 174 175 171 163 E-N NO 200 137 139 139 140 140 140 140 D-O NO2 322 87 88.5 69 34 34.5 31 23 F-P Downstream 83 Three columns on the right side of table 4.1.5 give reference to the actual data log in appendix 4, provide a guide on how to read the table and refer to related appendix for the data in respective rows.

4.1.6 Measurement with Urea Spray and 4 SCR bricks.

The test results with urea spray and 4 SCR bricks are summarized in the table 4.1.6. The same methodology used for Urea Spray with 1 SCR was utilised in this test. The main differences from the 1 SCR case is the NOx reading downstream of the SCR. Clearly in this test, excess ammonia from urea spray have reduced all of NOx but posses another problem in the system. The undesired NH 3 slippages have been detected and further analysis in the section 4.1.6 will discuss this in depth. Table 4.1.6 Summary of Result: Urea Spray with 4 SCR. all measurements in ppm Results for urea spray 4 SCRs Temp upstream 592 K Temp downstream 582 K O2 upstream

9.30 O2 downstream

7.90 4 SCRs Spray pulse length ms -- 24 26 28 30 32 34 36 Refn Guide Apdx Potential up 4SCR Pot NH3 552 614 696 818 888 960 1042 calc A 3.6.2 Potential up 4SCR Pot SUM 510 1062 1124 1206 1328 1398 1470 1552 nh3+nox B MEXA up 4SCR SUM 544 797 813 837 858 878 904 908 avg sum C 4.1.6B MEXA, Spray off up 4SCR NO 200 200 200 200 200 200 200 200 240708b D 4.1.6 MEXA, Spray off up 4SCR NOx 510 510 510 510 510 510 510 510 240708b E 4.1.6 Calculated up 4SCR NO2 310 310 310 310 310 310 310 310 calc F MEXA Reading up 4SCR NH3 38 318 346 381 405 434 466 240708b G 4.1.6 Deduced ammonia up 4SCR SUM-NOx 34 287 303 327 348 368 394 398 240708b C-E=H 4.1.6 MEXA dw 4SCR SUM 539 78 128 181 242 304 367 424 avg sum I 4.1.6 MEXA dw 4SCR NO 205 30 5 1 1 1 2 20708c J 4.1.6 Measured dw 4SCR NH3 79 136 167 225 310 375 230708b K 4.1.6 NH3 + NO2 dw 4SCR SUM-NO 334 48 123 180 241 303 365 424 calc I-J=L Total consumed across 4 SCrs Pot SUM- SUM -29 984 996 1025 1086 1094 1103 1128 calc B-I=M Note: Plotted against potential ammonia supplied 4 SCR spray Pot NH3 up 552 614 696 818 888 960 1042 A up - down, 4SCR Pot SUM-SUM 4 SCR -29 984 996 1025 1086 1094 1103 1128 M 4SCR spray NOx or NH3consumed -15 492 498 512.5 543 547 551.5 564 M2=N 4SCR spray NO consumed -5 170 195 199 199 199 198 200 D-J=O 4SCR spray NO2 consumed -9.5 322 303 313.5 344 348 353.5 364 N-O =P concentration table pot NH3 up 552 614 696 818 888 960 1042 A Deduced ammonia ups 4SCR SUM-NOx 34 287 303 327 348 368 394 398 H NH3 14.5 60 116 183.5 275 341 408.5 478 A-N NOx 525 18 12 -2.5 -33 -37 -41.5 -54 E-N NO 205 30 5 1 1 1 2 D-O NO2 320 -12 7 -3.5 -34 -38 -43.5 -54 F-P Downstream 84 At the bottom of table 4.1.6 some of the NOx and NO 2 reading were showing negative values due to experimental error in this study using the methodology described earlier in the range of around +- 55 ppm. The NO 2 measurements were not measured directly but derived using the methodology described in section 4.1. It is believed that the negative values reflect the magnitude of the errors resulting from these assumptions, but do not affect the general conclusions discussed later.

4.2 Ammonia gas studies: General Overview

The test with 5 and 4 ammonia gas provide a comparison of SCR reaction in the form of gas as compared to aqueous ammonia solution. The ammonia input level can be determined from known exhaust mass flow rate and a calibrated flow meter. The advantages using ammonia gas is obviously to accelerate the SCR reaction to reduce NOx and eliminate the complication with the use of urea spray. The analyser response to the measurements also improved and also reduced analyser break down due to urea droplets penetrating the sampling lines and internal components of the analyser. Five cases are presented in this investigation involving four 5 tests and one 4 test.

4.2.1 Ammonia gas studies: upstream measurements. 1 and 4 SCR bricks

The measurements taken for the 4 and 5 ammonia gas were the SUM upstream and downstream of the SCR and the NO upstream and downstream of the SCR. The SUM in NOxNH 3 mode of the MEXA follows the equation below: SUM upstream = [NH 3 +NO +NO 2 ] upstream The NOx measurements upstream were obtained in the absence of ammonia gas injection and were assumed unchanged when ammonia gas was injected. This assumes that the gas phase reactions were negligible. In the MEXA NONO 2 mode, the NO measurements upstream, even in the presence of ammonia, should be the same as without the ammonia gas injection as the converter is bypassed. Similarly, the assumption made was no gas phase reactions occurred. Therefore, the NO 2 upstream can be deduced from NOx-NO and had the same value regardless of amount of ammonia injected. The NH 3 measurements recorded upstream were erroneous but the correct ammonia level could be obtained by calculation of SUM-true NOx. 85

4.2.2 Ammonia gas studies: downstream measurements. 1 and 4 SCR bricks