27
3.1.2 Engine Dynamometer
The engine dynamometer was an Eddy Current EC AG150 from Froude Consine rated at 150 kW 200 BHP and 500 Nm 370 lb-ft torque with maximum speed of 8000 rpm. The AG series is also
known as the air gap range of eddy current dynamometers which has been designed to be compact, robust and allow easy maintenance. The dynamometer is fitted with oil injected half couplings at
either end of a non-magnetic stainless steel shaft which is supported in grease lubricated, deep groove ball bearings.
The dynamometer casing houses twin magnetising coils that produce a retarding controllable magnetic field that resists the applied torque. Heat generated in this process is dissipated by cooling
water. Rotation of the casing is resisted by a precision strain gauge load cell that gives accurate measurement of total input torque, measurement accuracy of ±0.25 of full rated torque and a
speed measurement accuracy of ±1 RPM. The dynamometer has low inertia, bi-directional motion and high reliability.
3.1.3 Engine mass flow rate measurement
The engine mass flow rate was measured using a Ricardo mass flow meter coupled with a digital manometer. Prior to testing the flow meter was calibrated in the flow lab within the university. The
Ricardo mass flow meter was connected to a pre-calibrated nozzle on an air flow rig figure 3.1.3. A digital manometer was connected to the Ricardo mass flow meter and the air flow supply was
varied. The air pressure drop was recorded for every air flow rate supplied and a calibration chart was produced for use on the engine. The arrangement used for air flow meter calibration is shown in
figure 3.1.3 and the calibration chart is shown in Appendix 3.1.3.
. Figure 3.1.3 Ricardo mass flow meter calibration [Courtesy of S. Quadri]
28 On the engine the mass flow rate was measured with a Testo digital manometer in mmH
2
0 and later converted to gramseconds and was recorded throughout the investigation. The Ricardo mass flow
meter configuration with digital manometer is shown in figure 3.1.4
Figure 3.1.4 Ricardo mass flow meter measuring engine Mass Flow Rate MFR
3.2 Final SCR Exhaust build and commissioning.
The Selective Catalyst Reduction SCR exhaust system was built based on the parts supplied by EMCON Technologies Incorporated and catalysts supplied by Johnson Matthey and the finalized
drawing agreed in a quarterly review meeting at Coventry University. The details of the parts supplied are listed in appendix 3.2. The SCR exhaust system comprises a Diesel Particulate Filter
DPF, Diesel Oxidation Catalyst DOC, expansion chamber and nozzle, a narrow angled diffuser, SCR catalyst, bypass pipe and instrumentation modules. Figure 3.2 shows a schematic of the final
assembly. It has been designed in such a way so to provide approximately 1D flow for comparison with a 1D computational model. Details of the components are discussed later.
From the engine exhaust manifold outlet, the exhaust was connected to the Diesel Oxidation Catalyst DOC for NO, CO and HC oxidation. Diesel oxidation catalysts can reduce emissions of
particulate matter PM from 15 to 30 percent while hydrocarbons HC and carbon monoxide CO by over 90 percent within temperature interval of 20 to 30
C45.These processes can be described by the following chemical reactions.
Digital manometers
Ricardo mass flow meter
29 [HC] + O
2
CO
2
+ H
2
O Equation 3.2a
CO + 12O
2
CO
2
Equation 3.2b HC are oxidized to form carbon dioxide and water vapour. The reaction in equation 3.2a represents
two processes: the oxidation of gas phase HC and the oxidation of organic fraction of diesel particulates SOF compounds. Reaction in equation 3.2b describes the oxidation of carbon
monoxide to carbon dioxide. Since carbon dioxide and water vapour are considered harmless, the above reactions bring an obvious emission benefit. The most significant contribution of the DOC is to
oxidize incoming NO to NO
2
which allow fast SCR reaction to reduce NOx as described in the equation 3.2c
2NH
3
+ NO + NO
2
2N
2
+ 3H
2
O Equation 3.2c
Therefore, the arrangement where DPF and DOC were designed in this investigation was crucial to provide sufficient NONO
2
ratio for optimum SCR reaction. The first instrumentation module was connected to the DOC to accommodate the EXSA, MEXA analyser, lambda sensor and
thermocouples for measuring the exhaust emissions downstream of the DPF and DOC and also monitoring exhaust temperature.
Figure 3.2 Final Assembly of the SCR Exhaust System.
Bypass pipe
DOC DPF
30
3.2.1 SCR Exhaust Fabrications and Specifications.
The SCR exhaust fabrication took place at various facilities across the university, the local fabrication workshop at the university and also at the collaborating companies facilities of EMCON Technology
and Johnson Matthey.
Figure 3.2.1 The suspended exhaust from a square metal frame. The complete SCR exhaust system was suspended horizontally from a metal square frame with cable
wire as shown in figure 3.2.1. Sealing gaskets were placed in between each component. The gasket used was a high temperature resistance type in order to prevent gas leakage from the exhaust
system. Some minor adjustment was necessary in the final SCR exhaust assembly because of the restricted space within the cell.
3.2.2 DPF-DOC assembly.
The first component of the exhaust system comprises of DPF coupled with DOC. In the initial plan the DPF and DOC were to be connected in a vertical position but they were later repositioned due to
cell constraints and laid horizontally as in figure 3.2. A final assembly front view and isometric view drawing is shown in appendix 3.2b. A draining plug was fitted underneath the expansion box which
houses the spray assembly. Two DOC configurations were available for this investigation; a single DOC of diameter 115 mm and length 95 mm and a double DOC of the same diameter but of length
190 mm. This is shown in the DOC assembly drawing in appendix 3.2b.The details of DPF assembly are also shown in the DPF assembly drawing of appendix 3.2b. The detail specification of the DOC is
shown in table 3.2.2.
31 Table 3.2.2 Detail specification of the DOC catalyst
Diameter 118.4 mm with 115 mm exposed in rig
Length Single = 91 mm, Volume approximately 1 litre
Double = 182 mm, Volume approximately 2 litre Cell Density
400 cpsi Cell Pitch
1.27 mm Substrate
NGK HoneyCeram Wall Thickness
0.11 mm [4.3 thouUK,4.3 mil USA] Open frontal area non-washcoated
83.4 Bulk density of substrate
0.29 gcc 290 kgm
3
Washcoat thickness 0.085 mm
Washcoated channel dimension 1.076 mm
Washcoat loading assuming washcoat density = 1350 kgm
3
158.7 kgm
3
3.2.3 SCR Catalysts Assembly
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