| 1. |
- Ahmed, Ahfaz, et al.
(författare)
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Kinetic modelling and experimental study of small esters : Methyl acetate and ethyl acetate
- 2017
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Ingår i: 11th Asia-Pacific Conference on Combustion, ASPACC 2017. ; 2017-December
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Konferensbidrag (refereegranskat)abstract
- A detailed chemical kinetic mechanism comprising methyl acetate and ethyl acetate has been developed based on the previous work by Westbrook et al. [1]. The newly developed kinetic mechanism has been updated with new reaction rates from recent theoretical studies. To validate this model, shock tube experiments measuring ignition delay time have been conducted at 15 & 30 bar and equivalence ratio 0.5, 1.0 and 2.0. Another set of experiments measuring laminar burning velocity was also performed on a heat flux burner at atmospheric pressure over wide range of equivalence ratios [ ~ 0.7-1.4]. The new mechanism shows significant improvement in prediction of experimental data over earlier model across the range of experiments.In this study, a detailed chemical kinetic model for methyl and ethyl acetate (Fig. 1) has been developed. This model is advanced from the mechanism proposed for laminar premixed flames by Westbrook and coworkers in 2009 [1]. Acetates studied in this work are both high RON fuels with suitable physical and chemical properties [Table 1] to be considered as potential fuels in advanced gasoline engines [4]. Shock tube experiments measuring ignition delay time have been conducted at 15 & 30 bar and equivalence ratio 0.5, 1.0 and 2.0. Another set of experiments measuring laminar burning velocity have also been performed on a heat flux burner at atmospheric pressure over wide range of equivalence ratios. The model developed in this work shows good agreement with ignition data and laminar burning velocity data across the temperature and equivalence ratio range respectively.
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| 2. |
- Ahmed, Ahfaz, et al.
(författare)
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Small ester combustion chemistry : Computational kinetics and experimental study of methyl acetate and ethyl acetate
- 2019
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Ingår i: Proceedings of the Combustion Institute. - : Elsevier BV. - 1540-7489. ; 37:1, s. 419-428
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Tidskriftsartikel (refereegranskat)abstract
- Small esters represent an important class of high octane biofuels for advanced spark ignition engines. They qualify for stringent fuel screening standards and could be synthesized through various pathways. In this work, we performed a detailed investigation of the combustion of two small esters, MA (methyl acetate) and EA (ethyl acetate), including quantum chemistry calculations, experimental studies of combustion characteristics and kinetic model development. The quantum chemistry calculations were performed to obtain rates for H-atom abstraction reactions involved in the oxidation chemistry of these fuels. The series of experiments include: a shock tube study to measure ignition delays at 15 and 30 bar, 1000-1450 K and equivalence ratios of 0.5, 1.0 and 2.0; laminar burning velocity measurements in a heat flux burner over a range of equivalence ratios [0.7-1.4] at atmospheric pressure and temperatures of 298 and 338 K; and speciation measurements during oxidation in a jet-stirred reactor at 800-1100 K for MA and 650-1000 K for EA at equivalence ratios of 0.5, 1.0 and at atmospheric pressure. The developed chemical kinetic mechanism for MA and EA incorporates reaction rates and pathways from recent studies along with rates calculated in this work. The new mechanism shows generally good agreement in predicting experimental data across the broad range of experimental conditions. The experimental data, along with the developed kinetic model, provides a solid groundwork towards improving the understanding the combustion chemistry of smaller esters.
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| 3. |
- Lokachari, Nitin, et al.
(författare)
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A comprehensive experimental and kinetic modeling study of di-isobutylene isomers : Part 1
- 2023
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Ingår i: Combustion and Flame. - : Elsevier BV. - 0010-2180. ; 251
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Tidskriftsartikel (refereegranskat)abstract
- Di-isobutylene has received significant attention as a promising fuel blendstock, as it can be synthesized via biological routes and is a short-listed molecule from the Co-Optima initiative. Di-isobutylene is also popularly used as an alkene representative in multi-component surrogate models for engine studies of gasoline fuels. However, there is limited experimental data available in the literature for neat di-isobutylene under engine-like conditions. Hence, most existing di-isobutylene models have not been extensively validated, particularly at lower temperatures (< 1000 K). Most gasoline surrogate models include the di-isobutylene sub-mechanism published by Metcalfe et al. [1] with little or no modification. The current study is undertaken to develop a detailed kinetic model for di-isobutylene and validate the model using a wide range of relevant experimental data. Part 1 of this study exclusively focuses on the low- to intermediate temperature kinetics of di-isobutylene. An upcoming part 2 discusses the high-temperature model development and validation of the relevant experimental targets. Ignition delay time measurements for the di-isobutylene isomers were performed at pressures ranging from 15 – 30 bar at equivalence ratios of 0.5, 1.0, and 2.0 diluted in air and in the temperature range 650 – 900 K using two independent rapid compression machine facilities. In addition, measurements of species identified during the oxidation of these isomers were performed in a jet-stirred reactor and in a rapid compression machine. A detailed kinetic model for the di-isobutylene isomers is developed to capture the wide range of new experimental targets. For the first time, a comprehensive low-temperature chemistry submodel is included. The differences in the important reaction pathways for the accurate prediction of the oxidation of the two DIB isomers are compared using reaction path analysis. The most sensitive reactions controlling the ignition delay times of the DIB isomers under the pressure and temperature conditions necessary for autoignition in engines are identified.
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| 4. |
- Lokachari, Nitin, et al.
(författare)
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A comprehensive experimental and kinetic modeling study of di-isobutylene isomers : Part 2
- 2023
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Ingår i: Combustion and Flame. - : Elsevier BV. - 0010-2180. ; 251
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Tidskriftsartikel (refereegranskat)abstract
- A wide variety of high temperature experimental data obtained in this study complement the data on the oxidation of the two di-isobutylene isomers presented in Part I and offers a basis for an extensive validation of the kinetic model developed in this study. Due to the increasing importance of unimolecular decomposition reactions in high-temperature combustion, we have investigated the di-isobutylene isomers in high dilution utilizing a pyrolysis microflow reactor and detected radical intermediates and stable products using vacuum ultraviolet (VUV) synchrotron radiation and photoelectron photoion coincidence (PEPICO) spectroscopy. Additional speciation data at oxidative conditions were also recorded utilizing a plug flow reactor at atmospheric pressure in the temperature range 725–1150 K at equivalence ratios of 1.0 and 3.0 and at residence times of 0.35 s and 0.22 s, respectively. Combustion products were analyzed using gas chromatography (GC) and mass spectrometry (MS). Ignition delay time measurements for di-isobutylene were performed at pressures of 15 and 30 bar at equivalence ratios of 0.5, 1.0, and 2.0 diluted in ‘air’ in the temperature range 900–1400 K using a high-pressure shock-tube facility. New measurements of the laminar burning velocities of di-isobutylene/air flames are also presented. The experiments were performed using the heat flux method at atmospheric pressure and initial temperatures of 298–358 K. Moreover, data consistency was assessed with the help of analysis of the temperature and pressure dependencies of laminar burning velocity measurements, which was interpreted using an empirical power-law expression. Electronic structure calculations were performed to compute the energy barriers to the formation of many of the product species formed. The predictions of the present mechanism were found to be in adequate agreement with the wide variety of experimental measurements performed.
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