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Research Papers: Fuel Combustion

Efficacy of Add-On Hydrous Ethanol Dual Fuel Systems to Reduce NOx Emissions From Diesel Engines

[+] Author and Article Information
Jeffrey T. Hwang

Mechanical Engineering,
University of Minnesota,
111 Church Street SE,
Minneapolis, MN 55455
e-mail: hwang183@umn.edu

Alex J. Nord

Mechanical Engineering,
University of Minnesota,
111 Church Street SE,
Minneapolis, MN 55455
e-mail: nord0537@umn.edu

William F. Northrop

Mem. ASME
Mechanical Engineering,
University of Minnesota,
111 Church Street SE,
Minneapolis, MN 55455
e-mail: wnorthro@umn.edu

Contributed by the Internal Combustion Engine Division of ASME for publication in the JOURNAL OF ENERGY RESOURCES TECHNOLOGY. Manuscript received February 13, 2017; final manuscript received February 27, 2017; published online March 30, 2017. Assoc. Editor: Stephen A. Ciatti.

J. Energy Resour. Technol 139(4), 042206 (Mar 30, 2017) (9 pages) Paper No: JERT-17-1072; doi: 10.1115/1.4036252 History: Received February 13, 2017; Revised February 27, 2017

Aftermarket dual-fuel injection systems using a variety of different fumigants have been proposed as alternatives to expensive after-treatment to control NOx emissions from legacy diesel engines. However, our previous work has shown that available add-on systems using hydrous ethanol as the fumigant achieve only minor benefits in emissions without recalibration of the diesel fuel injection strategy. This study experimentally re-evaluates a novel aftermarket dual-fuel port fuel injection (PFI) system used in our previous work, with the addition of higher flow injectors to increase the fumigant energy fraction (FEF), defined as the ratio of energy provided by the hydrous ethanol on a lower heating value (LHV) basis to overall fuel energy. Results of this study confirm our earlier findings that as FEF increases, NO emissions decrease, while NO2 and unburned ethanol emissions increase, leading to no change in overall NOx. Peak cylinder pressure and apparent rates of heat release are not strongly dependent on FEF, indicating that in-cylinder NO formation rates by the Zel'dovich mechanism remain the same. Through single zone modeling, we show the feasibility of in-cylinder NO conversion to NO2 aided by unburned ethanol. The modeling results indicate that NO to NO2 conversion occurs during the early expansion stroke where bulk gases have temperature in the range of 1150–1250 K. This work conclusively proves that aftermarket dual fuel systems for fixed calibration diesel engines cannot reduce NOx emissions without lowering peak temperature during diffusive combustion responsible for forming NO in the first place.

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References

Figures

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Fig. 1

Diagram of engine test setup

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Fig. 2

In-cylinder pressure traces and apparent RoHR for mode 3 and 180 proof hydrous ethanol

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Fig. 3

Brake specific CO emissions as a function of FEF for 160 and 180 proof hydrous ethanol

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Fig. 4

Selected HC emissions on a brake-specific basis as a function of FEF for 160 and 180 proof hydrous ethanol at mode3

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Fig. 5

Brake specific unburned ethanol emissions as a function of FEF for 160 and 180 proof hydrous ethanol

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Fig. 6

Soot concentration as a function of FEF for 160 and 180 proof hydrous ethanol

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Fig. 7

Brake specific NO emissions as a function of FEF for 160 and 180 proof hydrous ethanol

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Fig. 8

Brake specific NOx emissions as a function of FEF for 160 and 180 proof hydrous ethanol

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Fig. 9

NO2/NOx ratio as a function of unburned ethanol for all modes and ethanol proofs

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Fig. 10

NO2/NOx ratio as a function of reaction temperature for selected HCs using a constant pressure reactor

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Fig. 11

Apparent RoHR, in-cylinder pressure, mean in-cylinder temperature, and CA90 temperature range as a function of CAD

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Fig. 12

NO conversion trajectory as a function of CAD starting at CA90

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Fig. 13

NO2/NOX contour as a function of local in-cylinder temperatures at CA90 and normalized unburned ethanol concentrations

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