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Research Papers

# Investigation of NO2 Formation Kinetics in Dual-Fuel Engines With Lean Premixed Methane–Air Charge

[+] Author and Article Information
Ehsan Arabian

Lehrstuhl f. Thermodynamik,
Technische Universität München,
Garching 85748, Germany,
e-mail: arabian@td.mw.tum.de

Thomas Sattelmayer

Professor
Lehrstuhl f. Thermodynamik,
Technische Universität München,
Garching 85748, Germany
e-mail: Sattelmayer@td.mw.tum.de

1Corresponding author.

Manuscript received March 11, 2019; final manuscript received March 15, 2019; published online April 11, 2019. Editor: Jerzy T. Sawicki.

J. Eng. Gas Turbines Power 141(8), 081010 (Apr 11, 2019) (7 pages) Paper No: GTP-19-1107; doi: 10.1115/1.4043243 History: Received March 11, 2019; Revised March 15, 2019

## Abstract

A dual fuel engine concept with lean premixed methane–air charge ignited by a diesel pilot flame is highly promising for reducing NOx and soot emissions. One drawback of this combustion method, however, is the high nitric dioxide (NO2) emissions observed at certain operating points. The conditions leading to increased NO2 formation have been investigated using a batch reactor model in cantera. It has been found that the high emission levels of NO2 can be traced back to the mixing of small amounts of quenched CH4 with NO from the hot combustion zones followed by postoxidation in the presence of O2, requiring that the temperatures are within a certain range. NO2 formation in the exhaust duct of a test engine has been modeled and compared to the experimental results. The well-stirred reactor model has been used that calculates the steady-state of a uniform composition for a certain residence time. An appropriate reaction mechanism that considers the effect of NO/NO2 on methane oxidation at low temperature levels has been used. The numerical results of NO–NO2 conversion in the duct at low temperature levels show good agreement with the experimental results. The partial oxidation of CH4 can be predicted well. It can be shown that methane oxidation in the presence of NO/NO2 at low temperature levels is enhanced via the reaction steps $CH3+NO2⇌CH3O+NO$ and $CH3O2+NO⇌CH3O+NO2$. In addition, the elementary reaction $HO2+NO⇌NO2+OH$ is the important NO oxidizing step.

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## Figures

Fig. 1

XNO (———) and XNO2 (– – – – –) at equilibrium state

Fig. 2

Xi (———) and temperature (– – – – –) evolution for a methane-air mixture; initial conditions: Φ = 0.5, T = 1200 K, P = 100 bar

Fig. 3

Xi (———) and temperature (– – – – –) evolution for a methane-air-NO mixture; initial conditions: Φ = 0.5, XNO = 1000 ppm, T = 1200 K, P = 100 bar

Fig. 4

Xi (———) and temperature (– – – – –) evolution for a methane-air-NO mixture. Initial conditions: XCH4=1000 ppm, XNO = 500 ppm, sc = 0.21, XN2=0.79, T = 1000 K, P = 100 bar.

Fig. 5

XNO2 evolution in the absence of: O2 (); NO (); CH4 ()

Fig. 6

Effect of CH4 concentration on NO2/NOx (———) and XCH4 (– – – – –) evolution. Initial conditions: XO2=0.1, XNO = 700 ppm, XN2=0.75, XCO2=0.05, XH2O=0.1, T = 1000 K, P = 100 bar.

Fig. 7

Effect of temperature on NO2/NOx (———) and XCH4 (––– – –) evolution predicted by Glarborg mechanism. Initial conditions: XCH4=1000 ppm, XO2=0.1, XNO = 700 ppm, XN2=0.75,XCO2=0.05, XH2O=0.1, P = 100 bar.

Fig. 8

Effect of temperature on NO2/NOx (———) and XCH4 (––– – –) evolution predicted by GRI-3.0 mechanism. Initial conditions: XCH4=1000 ppm, XO2=0.1, XNO = 700 ppm, XN2=0.75, XCO2=0.05, XH2O=0.1, P = 100 bar.

Fig. 9

Reaction path diagram during NO2 formation. Left: Glarborg mechanism; right: GRI-3.0 mechanism.

Fig. 10

Man DF test engine exhaust duct

Fig. 11

Comparison of measured and simulated “NO2,” “NO,” “CH4,” and “CO” mole fraction in exhaust duct at full load

Fig. 12

Comparison of measured and simulated NO2 formation in exhaust duct at partial load

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