Diesel Fuel Effects on Emissions: Towards a Better Understanding

A continued challenge to engine combustion simulation is predicting the impact of fuel-composition variability on performance and emissions. Diesel fuel properties, such as cetane number, aromatic content and volatility, significantly impact combustion phasing and emissions. Capturing such fuel property effects is critical to predictive engine combustion modeling. In this work, we focus on accurately modeling diesel fuel effects on combustion and emissions. Engine modeling is performed with 3D CFD using multi-component fuel models, and detailed chemical kinetics. Diesel FACE fuels (Fuels for Advanced Combustion Engines) have been considered in this study as representative of street fuel variability. The CFD modeling simulates experiments performed at Oak Ridge National Laboratory (ORNL) [1] using the diesel FACE fuels in a light-duty single-cylinder direct-injection engine. These ORNL experiments evaluated fuel effects on combustion phasing and emissions. The actual FACE fuels are used directly in engine experiments while surrogate-fuel blends that are tailored to represent the FACE fuels are used in the modeling. The 3D CFD simulations include spray dynamics and turbulent mixing. We first establish a methodology to define a model fuel that captures diesel fuel property effects. Such a model should be practically useful in terms of acceptable computational turnaround time in engine CFD simulations, even as we use sophisticated fuel surrogates and detailed chemistry. Towards these goals, multi-component fuel surrogates have been developed for several FACE fuels, where the associated kinetics mechanisms are available in a model-fuels database. A surrogate blending technique has been employed to generate the multi-component surrogates, so that they match selected FACE fuel properties such as cetane number, chemical classes such as aromatics content, T50 and T90 distillation points, lower heating value and H/C molar ratio. Starting from a well validated comprehensive gas-phase chemistry, an automated method has been used for extracting a reduced chemistry that satisfies desired accuracy and is reasonable for use in CFD. Results show the level of modeling necessary to capture fuel-property trends under these widely varying engine conditions.

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Fuel Effects on Particulate Emissions from D.I. Engine - Relationship among Diesel Fuel, Exhaust Gas and Particulates

10.4271/971605 ◽

1997 ◽

Cited By ~ 5

Author(s):

Tadao Ogawa ◽

Kiyomi Nakakita ◽

Minoru Yamamoto ◽

Masanori Okada ◽

Yoshio Fujimoto

Keyword(s):

Diesel Fuel ◽

Particulate Emissions ◽

Exhaust Gas ◽

Fuel Effects

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Fuel Effects on Particulate Emissions from D.I. Engines - Precise Analyses and Evaluation of Diesel Fuel

10.4271/2000-01-2882 ◽

2000 ◽

Cited By ~ 1

Author(s):

Tadao Ogawa ◽

Masae Inoue ◽

Keiko Fukumoto ◽

Yoshio Fujimoto ◽

Masanori Okada

Keyword(s):

Diesel Fuel ◽

Particulate Emissions ◽

Fuel Effects

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Diesel Fuel Lubricity - Base Fuel Effects

10.4271/2001-01-1928 ◽

2001 ◽

Cited By ~ 11

Author(s):

Ken Mitchell

Keyword(s):

Diesel Fuel ◽

Fuel Effects ◽

Fuel Lubricity

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Comparison of Petroleum and Alternate-Source Diesel Fuel Effects on Light-Duty Diesel Emissions

10.4271/831712 ◽

1983 ◽

Cited By ~ 1

Author(s):

Bruce B. Bykowski ◽

Charles T. Hare ◽

Robert L. Mason ◽

Thomas M. Baines

Keyword(s):

Diesel Fuel ◽

Diesel Emissions ◽

Light Duty ◽

Alternate Source ◽

Fuel Effects

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Experimental Study of Diesel Fuel Effects on Direct Injection (DI) Diesel Engine Performance and Pollutant Emissions

Energy & Fuels ◽

10.1021/ef070149x ◽

2007 ◽

Vol 21 (5) ◽

pp. 2642-2654 ◽

Cited By ~ 14

Author(s):

Theodoros C. Zannis ◽

Dimitrios T. Hountalas ◽

Roussos G. Papagiannakis

Keyword(s):

Experimental Study ◽

Diesel Engine ◽

Diesel Fuel ◽

Direct Injection ◽

Engine Performance ◽

Pollutant Emissions ◽

Di Diesel Engine ◽

Fuel Effects

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Effect of the hydrocarbon molecular structure in diesel fuel on the in-cylinder soot formation and exhaust emissions

International Journal of Engine Research ◽

10.1243/146808705x7400 ◽

2005 ◽

Vol 6 (3) ◽

pp. 187-205 ◽

Cited By ~ 16

Author(s):

K Nakakita ◽

K Akihama ◽

W Weissman ◽

J T Farrell

Keyword(s):

Molecular Structure ◽

Diesel Fuel ◽

Exhaust Emissions ◽

Combustion Characteristics ◽

Unexpected Result ◽

Single Cylinder ◽

Soot Precursors ◽

Class 1 ◽

Fuel Effects ◽

Load Conditions

Evaluations of diesel fuel effects on combustion and exhaust emissions in single-cylinder direct-injection diesel engines led to the unexpected result that a Swedish ‘class 1’ fuel generated more particulate matter (PM) than a fuel denoted ‘improved’, even though ‘class 1’ fuel had much lower distillation temperatures, aromatic concentration, sulphur level, and density than the ‘improved’ fuel. Little differences were observed in the combustion characteristics between these fuels, but detailed compositional analyses showed that ‘class 1’ fuel contains higher levels of cyclic and/or branched paraffins. Subsequent investigations in a laboratory flow reactor showed that ‘class 1’ fuel produces more soot precursors such as benzene and acetylene than the ‘improved’ fuel. In addition, experiments in a low-pressure laminar flame apparatus and shock tube with model (single-molecule) paraffin fuels showed that isoparaffins and cycloparaffins generate more soot precursors and soot than n-paraffins do. These results strongly suggested that the effect of molecular structure on exhaust PM formation should be more carefully examined. Therefore, a new series of investigations were performed to examine exhaust emissions and combustion characteristics in single-cylinder engines, with well-characterized test fuels having carefully controlled molecular composition and conventional distillation characteristics and cetane numbers (CNs). These investigations revealed the following. Firstly, under low and medium loads, cycloparaffins (naphthenes) have a higher PM formation tendency than isoparaffins and n-paraffins. Under high-load conditions, however, the paraffin molecular structure has a very small effect. Secondly, a highly n-paraffinic fuel does not yield PM reductions as high as expected, due to its high CN and corresponding shorter ignition lag, which initiates combustion under a state of insufficient fuel-air mixing. This finding was corroborated by laser-induced incandescence analyses. Thirdly, the lowest PM emissions were observed with a paraffinic fuel containing 55 per cent isoparaffins and 39 per cent n-paraffins. Fourthly, aromatics give higher soot and PM levels than paraffins do at high and medium load conditions. Smaller differences are observed at lower speeds and loads. Fifthly, the best fit to the PM emissions was obtained with an equation containing the regression variables CN, aromatic rings, and naphthene rings. This expression of the fuel effects in chemical terms allows well-to-wheel analyses of refining and vehicle impacts resulting from molecularly based fuel changes.

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