D. Healy

National University of Ireland, Galway, Gaillimh, Connaught, Ireland

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Publications (10)9.64 Total impact

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    ABSTRACT: An experimental and kinetic modeling study of the autoignition of 3-methylheptane, a compound representative of the high molecular weight lightly branched alkanes found in large quantities in conventional and synthetic aviation kerosene and diesel fuels, is reported. Shock tube and rapid compression machine ignition delay time measurements are reported over a wide range of conditions of relevance to combustion engine applications: temperatures from 678 to 1356 K; pressures of 6.5, 10, 20, and 50 atm; and equivalence ratios of 0.5, 1.0, and 2.0. The wide range of temperatures examined provides observation of autoignition in three reactivity regimes, including the negative temperature coefficient (NTC) regime characteristic of paraffinic fuels. Comparisons made between the current ignition delay measurements for 3-methylheptane and previous results for n-octane and 2-methylheptane quantifies the influence of a single methyl substitution and its location on the reactivity of alkanes. It is found that the three C8 alkane isomers have indistinguishable high-temperature ignition delay but their ignition delay times deviate in the NTC and low-temperature regimes in correlation with their research octane numbers. The experimental results are compared with the predictions of a proposed kinetic model that includes both high- and low-temperature oxidation chemistry. The model mechanistically explains the differences in reactivity for n-octane, 2-methylheptane, and 3-methylheptane in the NTC through the influence of the methyl substitution on the rates of isomerization reactions in the low-temperature chain branching pathway, that ultimately leads to ketohydroperoxide species, and the competition between low-temperature chain branching and the formation of cyclic ethers, in a chain propagating pathway.
    Proceedings of the Combustion Institute 06/2013; 34(1):335-343. · 2.37 Impact Factor
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    ABSTRACT: Ignition delay time measurements were recorded at equivalence ratios of 0.3, 0.5, 1, and 2 for n-butane at pressures of approximately 1, 10, 20, 30 and 45 atm at temperatures from 690 to 1430 K in both a rapid compression machine and in a shock tube. A detailed chemical kinetic model consisting of 1328 reactions involving 230 species was constructed and used to validate the delay times. Moreover, this mechanism has been used to simulate previously published ignition delay times at atmospheric and higher pressure. Arrhenius-type ignition delay correlations were developed for temperatures greater than 1025 K which relate ignition delay time to temperature and concentration of the mixture. Furthermore, a detailed sensitivity analysis and a reaction pathway analysis were performed to give further insight to the chemistry at various conditions. When compared to existing data from the literature, the model performs quite well, and in several instances the conditions of earlier experiments were duplicated in the laboratory with overall good agreement. To the authors’ knowledge, the present paper presents the most comprehensive set of ignition delay time experiments and kinetic model validation for n-butane oxidation in air.
    Combustion and Flame. 08/2010;
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    ABSTRACT: Autoignition delay time measurements were recorded for blends of CH4/n-C4H10 in “air” at pressures of approximately 10, 16, 20, 25, and 30 atm from fuel-lean to fuel-rich conditions at two different fuel compositions, 90% CH4/10% n-C4H10 and 70% CH4/30% n-C4H10, and temperatures from 660 to 1330 K in both a rapid compression machine and a shock-tube facility. A detailed chemical kinetic model consisting of 1328 reactions involving 230 species was validated using the ignition delay data from this study. This mechanism has already been used to simulate previously published ignition delay times over a wide range of conditions. It was found that the model quantitatively reproduces the ignition delays from both rapid compression and reflected shock waves, accurately capturing reactivity as a function of the temperature, pressure, equivalence ratio, and fuel composition.
    Energy & Fuels 02/2010; 24(3). · 2.85 Impact Factor
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    ABSTRACT: Rapid compression machine (RCM) and shock-tube facilities have been employed to study the oxidation of natural gas blends at high pressure and intermediate to high temperatures. The use of both types of facilities allows a broad temperature envelope to be investigated and therefore encompasses the complete range applicable to gas turbines. A detailed chemical kinetic mechanism has been developed to simulate these results and will be used to approximate similar fuels. Mixtures of CH4/C2H6/C3H8/n-C4H10/n-C5H12 have been studied in the temperature range 630−1550 K, in the pressure range 8−30 bar, and at equivalence ratios of 0.5, 1.0, and 2.0 in “air”. For shock-tube experiments, the diluent gas was nitrogen, whereas in the RCM experiments the diluent gas composition ranged from pure nitrogen (at lower temperatures) to pure argon (at the highest temperatures). In addition, the combustion chamber in the RCM was fitted with a thermostat and heating tape to control and vary the initial temperature thereby varying the compressed gas temperature. Because the time-scale of a rapid compression machine experiment is so long, heat losses are significant. Thus, a series of nonreactive experiments were performed in order to account for the heat loss associated with each mixture composition and pressure.
    Energy & Fuels - ENERG FUEL. 02/2010; 24(3).
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    ABSTRACT: Rapid compression machine and shock-tube ignition experiments were performed for real fuel/air isobutane mixtures at equivalence ratios of 0.3, 0.5, 1, and 2. The wide range of experimental conditions included temperatures from 590 to 1567K at pressures of approximately 1, 10, 20, and 30atm. These data represent the most comprehensive set of experiments currently available for isobutane oxidation and further accentuate the complementary attributes of the two techniques toward high-pressure oxidation experiments over a wide range of temperatures. The experimental results were used to validate a detailed chemical kinetic model composed of 1328 reactions involving 230 species. This mechanism has been successfully used to simulate previously published ignition delay times as well. A thorough sensitivity analysis was performed to gain further insight to the chemical processes occurring at various conditions. Additionally, useful ignition delay time correlations were developed for temperatures greater than 1025K. Comparisons are also made with available isobutane data from the literature, as well as with 100% n-butane and 50–50% n-butane–isobutane mixtures in air that were presented by the authors in recent studies. In general, the kinetic model shows excellent agreement with the data over the wide range of conditions of the present study.
    Combustion and Flame - COMBUST FLAME. 01/2010; 157(8):1540-1551.
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    ABSTRACT: Rapid compression machine (RCM) and shock-tube facilities have been employed to study the oxidation of natural gas blends at high pressure and intermediate- to high-temperatures. The use of both types of facilities allows a broad temperature envelope to be investigated and therefore encompasses the complete range applicable to gas turbines. A detailed chemical kinetic mechanism has been developed to simulate these results and will be used to approximate similar fuels. Mixtures of CH4 / C2H6 / C3H8 / n-C4H10 / n-C5H12 have been studied in the temperature range 630- 1540 K, in the pressure range 8-30 atm and at equivalence ratios of 0.5, 1.0 and 2.0 in 'air'. For shock-tube experiments the diluent gas was nitrogen whereas in the RCM experiments the diluent gas composition ranged from pure nitrogen (at lower temperatures) to pure argon (at the highest temperatures). In addition, the combustion chamber in the RCM was fitted with a thermostat and heating tape to control and vary the initial temperature thereby varying the compressed gas temperature. Because the timescale of a rapid compression machine experiment is so long heat loss are significant. Thus, a series of non-reactive experiments were performed in order to account for the heat loss associated with each mixture composition and pressure.
    01/2009;
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    ABSTRACT: The oxidation of methane/ethane/propane mixtures, for blends containing 90/6.6/3.3, 70/15/15 and 70/20/10 percent by volume of each fuel respectively in ‘air,’ has been studied over the temperature range 770–1580 K, at compressed gas pressures of approximately 1, 10, 20, 30, 40 and 50 atm, and at equivalence ratios of 0.5, 1.0 and 2.0 using both a high-pressure shock tube and a rapid compression machine. The present work represents the most comprehensive set of methane/ethane/propane ignition delay time measurements available in a single study which extends the composition envelope over an industrially relevant pressure range. It is also the first such study to present ignition delay times at significantly overlapping conditions from both a rapid compression machine and a shock tube. The data were simulated using a detailed chemical kinetic model comprised of 289 species and 1580 reactions. It was found that qualitatively, the model reproduces correctly the effect of change in equivalence ratio and pressure, predicting that fuel-rich, high-pressure mixtures ignite fastest while fuel-lean, low-pressure mixtures ignite slowest. Moreover, the reactivity as a function of temperature is well captured with the model predicting negative temperature coefficient behavior similar to the experiments. Quantitatively the model is in general excellent agreement with the experimental results but is faster than experiment for the fuel-rich (ϕ=2.0) mixture containing the highest quantity of propane (70/15/15 mixture) at the lowest temperatures (770–900 K).
    Combustion and Flame 11/2008; · 3.60 Impact Factor
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    ABSTRACT: The oxidation of propane has been studied in the temperature range 680–970 K at compressed gas pressures of 21, 27, and 37 atm and at varying equivalence ratios of 0.5, 1.0, and 2.0. These data are consistent with other experiments presented in the literature for alkane fuels in that, when ignition delay times are plotted as a function of temperature, a characteristic negative coefficient behavior is observed. In addition, these data were simulated using a detailed chemical kinetic model. It was found that qualitatively the model correctly simulated the effect of change in equivalence ratio and pressure, predicting that fuel-rich, high-pressure mixtures ignite fastest, while fuel-lean, low-pressure mixtures ignite slowest. Moreover, reactivity as a function of temperature is well captured, with the model predicting negative temperature coefficient behavior similar to the experiments. Quantitatively the model is faster than experiment for all mixtures at the lowest temperatures (650–750 K) and is also faster than experiment throughout the entire temperature range for fuel-lean mixtures.
    Combustion and Flame. 01/2008; 153:316-333.
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    ABSTRACT: High-pressure experiments and chemical kinetics modeling were performed to generate a database and a chemical kinetic model that can characterize the combustion chemistry of methane-based fuel blends containing significant levels of heavy hydrocarbons (up to 37.5% by volume). Ignition delay times were measured in two different shock tubes and in a rapid compression machine at pressures up to 34 atm and temperatures from 740 to 1660 K. Laminar flame speeds were also measured at pressures up to 4 atm using a high-pressure vessel with optical access. Two different fuel blends containing ethane, propane, n-butane, and n-pentane added to methane were studied at equivalence ratios varying from lean (0.3) to rich (2.0). This paper represents the most comprehensive set of experimental ignition and laminar flame speed data available in the open literature for CH4 /C2 H6 /C3 H8 /C4 H10 /C5 H12 fuel blends with significant levels of C2+ hydrocarbons. Using these data, a detailed chemical kinetics model, based on current and recent work by the authors, was compiled and refined. The predictions of the model are very good over the entire range of ignition delay times, considering the fact that the data set is so thorough. Nonetheless, some improvements to the model can still be made with respect to ignition times at the lowest temperatures and for the laminar flame speeds at pressures above 1 atm and rich conditions.
    ASME Turbo Expo 2008: Power for Land, Sea, and Air; 01/2008
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    ABSTRACT: A chemical kinetics mechanism designed for the oxidation of methane-hydrocarbon blends at elevated pressures was used to study the effect of higher-order hydrocarbons on ignition delay time and flame speed at gas turbine conditions. The mechanism was developed from recent data and modeling conducted by the authors, including pressures above 30 atm, temperatures as low as 700 K, and alkane additives from C2 H6 through C5 H12 . Calculations focused on three target natural gas mixtures containing CH4 mole fractions from 62.5 to 98%. The results show the effects that pressure, temperature, and hydrocarbon content have on the combustion chemistry of the fuel-air mixtures. For example, autoignition times exhibit nonlinear trends with increasing pressure and decreasing temperature. Experiments in the authors’ laboratories are ongoing, and an overview of the related facilities is provided.
    ASME Turbo Expo 2007: Power for Land, Sea, and Air; 01/2007

Publication Stats

41 Citations
9.64 Total Impact Points

Institutions

  • 2007–2013
    • National University of Ireland, Galway
      • Combustion Chemistry Centre
      Gaillimh, Connaught, Ireland
  • 2008–2010
    • University of Central Florida
      • Department of Mechanical and Aerospace Engineering
      Orlando, FL, United States