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Research Papers: Internal Combustion Engines

Oxygen Enhanced Exhaust Gas Recirculation for Compression Ignition Engines

[+] Author and Article Information
T. Salt

 Associated Electric Cooperative, Inc., Clifton Hill, MO 65244 tsalt@aeci.org

D. R. Tree

 Brigham Young University, Provo, UT 84602 treed@byu.edu

C. Kim

 Kyungnam University, Masan, Kyungnam, Koreakim612ch@kyungnam.ac.kr

J. Eng. Gas Turbines Power 134(3), 032801 (Dec 28, 2011) (9 pages) doi:10.1115/1.4005114 History: Received July 02, 2010; Revised November 04, 2011; Published December 28, 2011; Online December 28, 2011

The benefits of oxygen enhancement in conjunction with EGR on emissions were investigated in a single-cylinder direct injection diesel engine. Cylinder pressure, NOx , and particulate were measured for EGR sweeps with and without oxygen enhancement. In all cases, the total flow of oxygen to the cylinder was maintained constant. This was achieved by increasing cylinder pressure for typical EGR (N-EGR) and by adding oxygen to the intake stream for oxygen-enhanced EGR (O-EGR). The results show that O-EGR produced a substantially better combination of NOx and particulate than N-EGR. In the N-EGR cases, the EGR dilutes the oxidizer causing lower NOx and higher particulate. In O-EGR, flame temperature reduction leading to lower NOx is achieved by a combination of higher molar specific heats of CO2 and H2 O and dilution. Particulate emissions decreased or remain constant with increasing O-EGR. In addition to the obvious challenge of providing a source of oxygen to an engine, two operational challenges were encountered. First, as O-EGR was increased, the ratio of specific heats (Cp /Cv ) of the cylinder intake charge decreased and decreased the compression temperature, causing significant changes in ignition delay. These changes were compensated for in the experiments by increasing intake temperature but would be challenging to manage in transient engine operation. Second, the increased water concentration in the exhaust created difficulties in the exhaust system and was suspected to have produced a water emulsion in the oil.

Copyright © 2012 by American Society of Mechanical Engineers
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References

Figures

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Figure 4

Thermal efficiency versus EGR fraction. Data for each line is an average of three runs.

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Figure 5

NOx and particulate for N-EGR and O-EGR, φ∼0.33

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Figure 6

NOx and particulate for N-EGR and O-EGR, φ∼0.50

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Figure 7

NOx and particulate for N-EGR and O-EGR, φ∼0.65

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Figure 8

Percent reduction in indicated specific NOx with increased portion of intake gases coming from added O2

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Figure 9

Shift in the NOx -particulate tradeoff curve as the portion of added O2 in the intake gases is increased, φ = 0.48

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Figure 10

Close up of Fig. 9 showing shift in the NOx -particulate tradeoff curve as the portion of added O2 in the intake gases is increased, φ = 0.48

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Figure 11

Indicated specific NOx versus peak flame temp, φ∼0.33

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Figure 12

Indicated specific NOx versus peak flame temp, φ∼0.5

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Figure 1

Flow diagram of the engine, EGR, and intake system

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Figure 2

Apparent heat release rate for the N-EGR sweep at φ = 0.53. EGR levels for the sweep are shown in Table 2.

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Figure 3

Apparent heat release rate for the O-EGR sweep at φ = 0.48 after adjusting the intake temperature. For EGR levels, see Table 2.

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Figure 13

Indicated specific NOx as a function of peak flame temperature, φ∼0.65

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Figure 14

Impact of N2 concentration on NOx emissions as predicted by the Zeldovich mechanism

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Figure 15

Relative contributions to rise in N·CP from dilution and specific heat effect, N-EGR (φ = 0.67)

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Figure 16

Relative contributions to rise in N·CP from dilution and specific heat effects, O-EGR, φ = 0.64

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Figure 17

Equilibrium concentrations of dissociated species as a function of N·Cp for two test cases

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Figure 18

Impact of dissociation on temperature rise for two test cases

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Figure 19

Particulate as a function of T90 flame temperature, φ∼0.33

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Figure 20

Particulate as a function of T90 flame temperature, φ∼0.50

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Figure 21

Particulate as a function of T90 flame temperature, φ∼0.65

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Figure 22

Rich-flame equilibrium concentrations for representative EGR and O-EGR intake gas compositions

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