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Research Papers: Air Emissions From Fossil Fuel Combustion

The NOx and N2 O Emission Characteristics of an HCCI Engine Operated With n-Heptane

[+] Author and Article Information
Hailin Li

Department of Mechanical and Aerospace Engineering,  West Virginia University, Morgantown, WV 26506

W. Stuart Neill, Hongsheng Guo, Wally Chippior

 Institute for Chemical Process and Environmental Technology, National Research Council Canada, Ottawa, ON, Canada

J. Energy Resour. Technol 134(1), 011101 (Dec 23, 2011) (9 pages) doi:10.1115/1.4005243 History: Received August 13, 2010; Revised August 05, 2011; Published December 23, 2011; Online December 23, 2011

This paper presents the oxides of nitrogen (NOx ) and nitrous oxide (N2 O) emission characteristics of a Cooperative Fuel Research (CFR) engine modified to operate in homogeneous charge compression ignition (HCCI) combustion mode. N-heptane was used as the fuel in this research. Several parameters were varied, including intake air temperature and pressure, air/fuel ratio (AFR), compression ratio (CR), and exhaust gas recirculation (EGR) rate, to alter the HCCI combustion phasing from an overly advanced condition where knocking occurred to an overly retarded condition where incomplete combustion occurred with excessive emissions of unburned hydrocarbons (UHC) and carbon monoxide (CO). NOx emissions below 5 ppm were obtained over a fairly wide range of operating conditions, except when knocking or incomplete combustion occurred. The NOx emissions were relatively constant when the combustion phasing was within the acceptable range. NOx emissions increased substantially when the HCCI combustion phasing was retarded beyond the optimal phasing even though lower combustion temperatures were expected. The increased N2 O and UHC emissions observed with retarded combustion phasing may contribute to this unexpected increase in NOx emissions. N2 O emissions were generally less than 0.5 ppm; however, they increased substantially with excessively retarded and incomplete combustion. The highest measured N2 O emissions were 1.7 ppm, which occurred when the combustion efficiency was approximately 70%.

Copyright © 2012 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Schematic diagram of HCCI engine setup

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Figure 2

Effect of air/fuel ratio on the emissions of NOx , CO, and THC. CR = 10, Tin  = 30°C, Pin  = 95 kPa, Pexh  = 105 kPa, no EGR.

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Figure 3

Effect of air/fuel ratio on combustion efficiency and NOx emissions. CR = 10, Tin  = 30°C, Pin  = 95 kPa, Pexh  = 105 kPa, no EGR.

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Figure 4

Effect of air/fuel ratio on NOx and N2 O emissions. CR = 10, Tin  = 30°C, Pin  = 95 kPa, Pexh  = 106 kPa, no EGR.

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Figure 5

Effect of compression ratio on NOx and N2 O emissions. Pin  = 95 kPa, Tin  = 30°C, AFR = 50, no EGR.

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Figure 6

Effect of compression ratio on combustion efficiency and NOx emissions. Pin  = 95 kPa, Tin  = 30°C, AFR = 50, no EGR.

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Figure 7

Effect of EGR rate on NOx and N2 O emissions at constant air/fuel ratio. CR = 10, AFR = 40, Tin  = 50°C, Pin  = 95 kPa.

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Figure 8

Effect of EGR rate on combustion efficiency and NOx emissions at constant air/fuel ratio. CR = 10, AFR = 40, Tin  = 50°C, Pin  = 95 kPa.

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Figure 9

Effect of EGR rate on NOx and N2 O emissions at constant fuel flow rate. CR = 10, Tin  = 40–62°C. Pin  = 95 kPa, ṁfuel=0.395kg/h.

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Figure 10

Effect of EGR rate on NOx emissions and combustion efficiency at constant fuel flow rate. CR = 10, Tin  = 40–62°C, Pin  = 95 kPa, ṁfuel=0.395kg/h.

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Figure 11

Effect of intake pressure on NOx emissions. CR = 10, Tin  = 65–72°C, AFR = 22.5, EGR rate = 45%, Pexh  = Pin  + 15 kPa, ṁfuel=0.309−0.721kg/h.

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Figure 12

Effects of air/fuel ratio and compression ratio on NOx emissions. Pin  = 95 kPa, no EGR, Tin  = 30°C for AFR = 50; Tin  = 50°C for AFR = 40.

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Figure 13

Variations of NOx emissions with changes in combustion phasing. Pin  = 95 kPa, no EGR. Tin  = 30°C for AFR = 50, Tin  = 50°C for AFR = 40.

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Figure 14

Variations of combustion efficiency with changes in combustion phasing. Pin  = 95 kPa, no EGR. Tin  = 30°C for AFR = 50, Tin  = 50°C for AFR = 40.

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Figure 15

Variations of NOx emissions with changes in combustion phasing. AFR = 50; CR experiment: CR = 9–16, Tin  = 30°C. Intake temperature experiment: CR = 10, Tin  = 25–116°C.

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Figure 16

Variations of NOx emissions with change in combustion phasing obtained by varying EGR rate or compression ratio. Pin  = 95 kPa, ṁfuel=0.395kg/h. EGR experiment: Tin  = 40–62°C, CR = 10. CR experiment: Tin  = 50°C, no EGR.

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Figure 17

Comparison of NOx emission variations with change in combustion phasing obtained by different approaches. Operating conditions as described in Table 2.

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Figure 18

Correlation of NOx emissions with THC emissions. Operating conditions described in Table 2.

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Figure 19

Correlation of NOx emissions with combustion efficiency. Operating conditions described in Table 2.

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Figure 20

Correlation of N2 O emissions with combustion efficiency. Operating conditions described in Table 2.

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