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Title: A UNIFAC-Based Approach to Gasoline Droplet Evaporation and the Role of Oxygenates on PM Precursor Vaporization

Abstract

In some studies, a relationship has been observed between increasing ethanol content in gasoline and increased particulate matter (PM) emissions from vehicles equipped with spark ignition engines. The fundamental cause of the PM increase seen for moderate ethanol concentrations is not well understood. As a result, existing PM indices such as PMI may not be indicative of measured PM emissions for oxygenated biofuel blends. Ethanol features a greater heat of vaporization (HOV) than gasoline and also influences vaporization by altering the liquid and vapor composition throughout the vaporization process. A droplet vaporization model was developed to explore ethanol's effect on the evaporation of aromatic compounds known to be PM precursors. The evolving droplet composition is modeled as a distillation process, with non-ideal interactions between oxygenates and hydrocarbons accounted for using UNIFAC group contribution theory. Detailed hydrocarbon analysis was applied to fuel samples, and used as input for the initial droplet composition. The droplet can be modeled in terms of energy transfer, which in turn provides the transient mass transfer, droplet temperature, and droplet diameter. Model predictions suggest that non-ideal vapor-liquid equilibrium along with an increase in HOV can alter the droplet composition evolution. Results predict that the presence of ethanolmore » causes enrichment of the higher boiling fractions (T90+) in the aromatic components as well as lengthens the droplet lifetime. A simulation of the evaporation process in a transient environment as experienced within an engine cylinder predicts a decrease in mixing time of the heaviest fractions of the fuel prior to spark initiation, possibly explaining observations linking ethanol to PM. A correlation between liquid phase PM precursors and measured PM emissions is shown.« less

Authors:
 [1]; ORCiD logo [1];  [2];  [3];  [3]
  1. National Renewable Energy Laboratory (NREL), Golden, CO (United States)
  2. Colorado State University
  3. University of Colorado, Colorado Springs
Publication Date:
Research Org.:
National Renewable Energy Lab. (NREL), Golden, CO (United States)
Sponsoring Org.:
USDOE Office of Energy Efficiency and Renewable Energy (EERE)
OSTI Identifier:
1461256
Report Number(s):
NREL/CP-5400-71962
DOE Contract Number:  
AC36-08GO28308
Resource Type:
Conference
Resource Relation:
Conference: Presented at the 10th US Combustion Meeting 2017, 23-24 April 2017, College Park, Maryland
Country of Publication:
United States
Language:
English
Subject:
33 ADVANCED PROPULSION SYSTEMS; vaporization; ethanol; gasoline; precursors

Citation Formats

Ratcliff, Matthew A, McCormick, Robert L, Burke, Stephen, Rhoads, Robert, and Windom, Bret. A UNIFAC-Based Approach to Gasoline Droplet Evaporation and the Role of Oxygenates on PM Precursor Vaporization. United States: N. p., 2017. Web.
Ratcliff, Matthew A, McCormick, Robert L, Burke, Stephen, Rhoads, Robert, & Windom, Bret. A UNIFAC-Based Approach to Gasoline Droplet Evaporation and the Role of Oxygenates on PM Precursor Vaporization. United States.
Ratcliff, Matthew A, McCormick, Robert L, Burke, Stephen, Rhoads, Robert, and Windom, Bret. Fri . "A UNIFAC-Based Approach to Gasoline Droplet Evaporation and the Role of Oxygenates on PM Precursor Vaporization". United States.
@article{osti_1461256,
title = {A UNIFAC-Based Approach to Gasoline Droplet Evaporation and the Role of Oxygenates on PM Precursor Vaporization},
author = {Ratcliff, Matthew A and McCormick, Robert L and Burke, Stephen and Rhoads, Robert and Windom, Bret},
abstractNote = {In some studies, a relationship has been observed between increasing ethanol content in gasoline and increased particulate matter (PM) emissions from vehicles equipped with spark ignition engines. The fundamental cause of the PM increase seen for moderate ethanol concentrations is not well understood. As a result, existing PM indices such as PMI may not be indicative of measured PM emissions for oxygenated biofuel blends. Ethanol features a greater heat of vaporization (HOV) than gasoline and also influences vaporization by altering the liquid and vapor composition throughout the vaporization process. A droplet vaporization model was developed to explore ethanol's effect on the evaporation of aromatic compounds known to be PM precursors. The evolving droplet composition is modeled as a distillation process, with non-ideal interactions between oxygenates and hydrocarbons accounted for using UNIFAC group contribution theory. Detailed hydrocarbon analysis was applied to fuel samples, and used as input for the initial droplet composition. The droplet can be modeled in terms of energy transfer, which in turn provides the transient mass transfer, droplet temperature, and droplet diameter. Model predictions suggest that non-ideal vapor-liquid equilibrium along with an increase in HOV can alter the droplet composition evolution. Results predict that the presence of ethanol causes enrichment of the higher boiling fractions (T90+) in the aromatic components as well as lengthens the droplet lifetime. A simulation of the evaporation process in a transient environment as experienced within an engine cylinder predicts a decrease in mixing time of the heaviest fractions of the fuel prior to spark initiation, possibly explaining observations linking ethanol to PM. A correlation between liquid phase PM precursors and measured PM emissions is shown.},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = {2017},
month = {9}
}

Conference:
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