Experimental Setup

The engine used in this research was a Cummins ISM 2002 heavy duty engine.

Details of the engine are provided in the Table 4.1. Important changes affecting emissions in this engine are: an automatically controlled high pressure cooled EGR system, variable geometry turbocharging (VGT) with infinite adjustment which pro-vides the exact amount of boost at any engine speed. The engine is designed to

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Table 4.1: Details of the Cummins ISM 2002 heavy-duty Engine

Model Cummins ISM 2002

meet the 2.5 grams NO_X+NMHC^∗ emissions requirement for 2002. High pressure EGR systems recirculate the exhaust to the engine manifold via a restriction to in-crease its pressure above the intake manifold pressure. This results in a substantial fuel penalty [13, 64, 65]. With the use DPFs, cooled low pressure EGR systems are now being developed, in which the exhaust is recirculated from downstream of the particulate filter to upstream of the compressor where the pressure is close to ambient.

A schematic of the test cell is shown in Figure 4.1, adapted from reference The engine was coupled to an eddy current dynamometer manufactured by Eaton Cor-poration. It has a rating of 500 hp at speeds between 1750 rpm and 7000 rpm. A Digalog 1022A controller was used to control the load and speed on the engine. The air supply to the engine came from the test cell. The pressure drop across a laminar flow element and the temperature of the supply air was used to calculate the mass flow rate of air to the engine. Relative humidity was measured before the start of each experiment using a sling psychrometer. The pressure in the test cell during the experiment was measured using a mercury barometer. [46].

∗Non-Methane Hydrocarbons

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Figure4.1:Aschematicoftheexperimentalsetup(nottoscale)[46]

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The fuel mass flow rate to the engine was measured using an AVL fuel weigher.

The instrument allowed measurements of the time taken for the engine to consume 0.4 kg of diesel fuel, which, when divided, provided the average fuel mass flow rate during that period. The diesel fuel used in this research was ultra low sulfur diesel fuel (ULSF), with less than 1 ppmS present to 1) avoid catalyst poisoning in the DOC and CPF [2], 2) decrease sulfate formation downstream of the catalysts thus keeping TPM levels low [46] and 3) keeping the NO→NO₂ oxidation efficiency to a maximum [2]. An overview of the properties of the ULSF diesel fuel are shown in Table 4.2.

Temperatures in the DOC, CPF and ambient were measured using K-type ther-mocouples from Omega Engineering Inc., which were connected to a junction box in the test cell. Temperatures in the engine were measured using E-type thermocouples supplied by Cummins Inc., but were not connected to the junction box. The pres-sure drop across the DOC and CPF were meapres-sured using 13.8 kPad and 68.9 kPad differential pressure transducers respectively. %EGR was calculated by measuring the temperatures before after the recirculated exhaust mixes with the compressed aftercooled air supply to the engine (for derivation see reference [46]). Two SCXI modules, provided by National Instruments Inc., were used for signal processing and were linked to a data acquisition board and the data were recorded using Labview software by National Instruments Inc on a personal computer (PC). The recorded data were analyzed using Microsoft’s Excel spreadsheet software.R

Particle size distributions were measured by a scanning mobility particle sizer (SMPS) model 3077 made by TSI. The SMPS instrument uses an electric mobility detection technique. An electrostatic classifier charges particles to a known charge distribution and then classifies them according to their ability to pass through an electrical field and a condensation particle counter (CPC) measures their concentra-tion. The SMPS instrument was calibrated before use with the help of a manual

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Table 4.2: Properties of the ULSF diesel fuels used

Property ASTM No. Batch 2 (2/04-8/04) Batch 3 (8/04-10/04)

API gravity D-1298 39.1 39.4

Cetane index D-976 51.1 51.7

Sulfur content (ppm) D-4045 0.30 0.20

Distillation Profile

T10 (^oC) D-86 207 209

T50 (^oC) D-86 253 254

T90 (^oC) D-86 318 313

Fuel analysis (% Vol.)

Parafins & Napthenes D-1319 69.7 74.2

Olefins D-1319 3.0 0.8

Aromatics D-1319 27.3 25.0

provided by TSI. The measurements were made upstream of the DOC, downstream of the DOC and downstream of the CPF in the size range of 13.6nm to 763.5nm.

Three sets of particle size measurements were made at every location in the follow-ing order: upstream of the DOC, downstream of the DOC and downstream of the CPF, since only one location can sampled at any given time. A thermodenuder which removes the volatile and vapor contents in the sample lines prior to sampling [34], could not be used because it was being repaired by the manufacturer. A two-stage dilution system was used to dilute the sample exhaust so that near ambient particle concentrations enter the SMPS. It consists of a critical flow orifice in each stage of the device to assist in obtaining iso-kinetic sampling conditions and fixing the dilution ratio. In the absence of a thermodenuder a high total dilution ratio of 72.3 was used during the experiments to prevent particle nucleation and formation in the nuclei mode range [66, 67, 68]. For a details of the dilution system, orifice calibration and performance with pressure of supply air see the thesis of Lakkireddy [46]. To ensure that the SMPS drew the sample at the required rate, a T-section was connected when sampling upstream of the DOC and upstream of the CPF, as the back pressure at these locations forced excess air through the particle sample lines which made the SMPS lose its calibration (see [46] for setup). This was not necessary when sampling

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downstream of the CPF due to the absence of any backpressure. Prior to the start of each experiment, the particle size sample lines were cleaned with propanol and water and compressed air was blown through the lines to clean them. This was especially important for the downstream CPF sample line due to the low concentrations present that are reduced even further due to dilution. Once it was known that the CCRT ^R had very high filtration efficiencies, particle size measurements were first made down-stream of the CPF to determine the downdown-stream particle size distribution, so that the filtration efficiency could be calculated as a function of time. The sampling can be started using a PC and data obtained was converted to size distribution data using software provided by TSI Inc.

Gaseous emissions were measured with a Pierburg AMA 400 emissions analyzer at the following locations: upstream of the DOC, downstream of the DOC and down-stream of the CPF. The analyzer can simultaneously measure the concentrations of HCs, NO_X (or NO), CO, CO₂ and O₂ present in the sampled exhaust. Each set of readings taken at each location were carried out in the NO and NO_X modes so that the approximate NO₂ concentrations could be obtained by subtraction. The Pierburg AMA 400 analyzer uses a flame ionization detector to measure HCs, a non disper-sive infra red analyzers to measure CO and CO₂ concentrations, a chemiluminescence analyzer to measure NO_X and NO and an O₂ sensor to measure O₂ concentrations.

The analyzer reports the concentrations of CO2 and O2 on a dry fraction basis. The sampling locations were connected to the emissions analyzer by means of a heated line, which is maintained at 185^oC by the analyzer when measuring emissions in

’diesel’ mode. The switching between the sampling locations is done by means of fast acting pneumatically operated valves whose compressed air supply is from an air compressor in the test cell. This system and its design are described in the thesis of Lakkireddy [46]. Prior to the start of each experiment an internal leak check was per-formed to ensure that no leaks were present in the heated line or the instrument. The

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analyzer was controlled by a PC and the data recorded was analyzed using Microsoft’s Excel software.R

Carbonaceous particulate matter (CPM) samples were measured upstream of the DOC and downstream of the CPF. CPM concentrations measured upstream of the DOC were taken to be the concentrations entering the CPF as it can be assumed that CPM concentrations do not change across a DOC [14]. The sampling train, made by Anderson Instruments Inc., draws exhaust through a six-hole probe inserted in the exhaust line. CPM are collected on 47mm glass fiber filters (Pall Corporation), supported on an under drain disk and a screen to prevent the filters from damage. For a detailed description on the design of the sampling system see references [46, 69], and a schematic of the setup is reproduced in Figure 4.1 (from reference [46]) . The flow rate through the 47 mm filters was between 17-29 std-liters/min with a high volume stak sampler, maintained by keeping a constant pressure drop across a calibrated orifice. However, since the exhaust temperature varies with engine load, face velocities on the 47 mm filters during CPM collection were different during the experiments.

The samples were drawn through two tubes full of silica gel kept in an ice bath to absorb the moisture present in the sample exhaust. The 47 mm filters were weighed on a micro-balance manufactured by Metler Toledo Inc, with a maximum capacity of 2 g and an accuracy of 0.1 µg, before and after the experiment, to determine the increase in weight of the 47mm filters due to the deposited CPM. Prior to weighing, all the 47mm filters were conditioned in a humidity controlled chamber for 24 hours to provide a constant mass of water on each filter. Immediately after the experiments, the exposed 47mm filters were placed in an ammoniation chamber to convert the hygroscopic H₂SO₄.7H₂O to the less hygroscopic ammonium sulfate (NH₄)₂SO₄, thus avoiding an increase in weight of the samples due to pick up of moisture. Corrections to the weight, due to the samples being kept in the humidity controlled chamber were taken into account by also weighing a 47mm ’control’ filter which is always present

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Figure 4.2: A schematic of the CPM sampling system [46]