Experimental and modeling study of the autoignition of 1-hexene/iso-octane mixtures at low temperatures

Autoignition delay times have been measured in a rapid compression machine at Lille at temperatures after compression from 630 to 840 K, pressures from 8 to 14 bar, \Phi = 1 and for a iso octane/1 hexene mixture containing 82% iso-octane and 18% 1 hexene. Results have shown that this mixture is strongly more reactive than pure iso-octane, but less reactive than pure 1 hexene. It exhibits a classical low temperature behaviour, with the appearance of cool flame and a negative temperature coefficient region. The composition of the reactive mixture obtained after the cool flame has also been determined. A detailed kinetic model has been obtained by using the system EXGAS, developed in Nancy for the automatic generation of kinetic mechanisms, and an acceptable agreement with the experimental results has been obtained both for autoignition delay times and for the distribution of products. A flow rate analysis reveals that the crossed reactions between species coming from both reactants (like H-abstractions or combinations) are negligible in the main flow consumption of the studied hydrocarbons. The ways of formation of the main primary products observed and the most sensitive rate constants have been identified

Develop a Hazard Index Using Machine Learning Approach for the Hazard Identification of Chemical Logistic Warehouses

PresentationWith the rapid development of chemical process plants, the safe storage of hazardous chemicals become an essential topic. Several chemical warehouse incidents related to fire and explosion have been reported recently. Therefore, an accurate hazard identification method for the logistic warehouse is needed not only for the facility to develop a proper emergency response plan but also for the residents who live near the facility to have an effective hazard communication. Furthermore, the government can better allocate the resources for first responders to make fire protection strategies, and the stakeholders can lead to improved risk management. Hazard index is a helpful tool to identify and quantify the hazard in a facility or a process unit. The challenge for this research is to improve the current method with the novel technique to implement our purpose. The first objective of this research is to develop a “Storage Hazard Factor” (SHF) to evaluate and rank the inherent hazards of chemicals stored in logistic warehouses. In the factor calculation, the inherent hazard of chemicals is determined by various parameters (e.g., the NFPA rating, the flammability limit, and the protective action criteria values, etc.) and validated by the comparison with other indices. The current criteria for flammable hazard ratings are based on flash point, which is proved to be insufficient. Two machine learning based methods will be used for the classification of liquid flammability considering aerosolization based on DIPPR 801 database. Subsequently, SHF and other warehouse safety penalty factors (e.g., the quantity of the chemicals, the distance to the nearest fire department, etc.) are utilized to identify the Logistic Warehouse Hazard Index (LWHI) of the facilities. In the last chapter, this method is applied to real-time data from Houston Chronicle, and several statistical analyses are used to prove the hazard index is helpful for hazard identification to emergency responders and hazard communication to the public

Experimental and modeling study of the low-temperature oxidation of large alkanes

This paper presents an experimental and modeling study of the oxidation of large linear akanes (from C10) representative from diesel fuel from low to intermediate temperature (550-1100 K) including the negative temperature coefficient (NTC) zone. The experimental study has been performed in a jet-stirred reactor at atmospheric pressure for n-decane and a n-decane/n-hexadecane blend. Detailed kinetic mechanisms have been developed using computer-aided generation (EXGAS) with improved rules for writing reactions of primary products. These mechanisms have allowed a correct simulation of the experimental results obtained. Data from the literature for the oxidation of n-decane, in a jet-stirred reactor at 10 bar and in shock tubes, and of n-dodecane in a pressurized flow reactor have also been correctly modeled. A considerable improvement of the prediction of the formation of products is obtained compared to our previous models. Flow rates and sensitivity analyses have been performed in order to better understand the influence of reactions of primary products. A modeling comparison between linear alkanes for C8 to C16 in terms of ignition delay times and the formation of light products is also discussed

EXPERIMENTAL AND MODELING STUDY OF IGNITION-RESISTANT FUELS

This research investigates relative ignition behavior of some oxygenated fuels and their blends with gasoline surrogates. It seeks to identify fuels with higher resistance to ignition and validate tentative kinetic models intended to predict their combustion chemistry. It also develops a method for simplified ignition delay time correlation that can allow for a more rapid estimation of the ignition behavior of a given fuel at known thermodynamic conditions. The work is motivated by the fact that in spark-ignition (SI) engines, increasing energy conversion efficiency through increasing the engine compression ratio is limited by the phenomenon of undesired autoignition known as engine knock. This is controlled by the chemical kinetics of the fuels which can be modified toward higher resistance using fuels of higher ignition resistance. In this study, the ignition behavior of the representative fuels is studied using both shock tube experiments and simulations of the kinetics of homogeneous chemical reactors. Specifically, we study: 1) propanol isomers, which are alcohols with three carbon atoms and promising alternative fuels for gasoline fuels; 2) MTBE and ETBE, which are effective ignition-resistant fuel components; 3) blends of a gasoline with ETBE or iso-propanol, to establish the kinetic interactions. The resulting experimental data are used to validate current chemical kinetics models of the individual fuels. To further facilitate the use of fuel blends suggested by this study, combined chemical kinetic models are developed of iso-octane as a gasoline surrogate and each of ignition resistant fuels identified. In order to reduce the computational cost of using the validated detailed models of the fuels studied, reduced kinetic models are developed. These reduced versions are of two kinds. The first uses the model reduction method known as Alternate Species Elimination (ASE) to derive smaller versions of the detailed models. The second reduction approach focuses on the prediction of the chemical time scale associated with ignition. Here a generalized ignition format is developed and detailed model simulations are used to obtain the constraining data. This makes it possible to predict ignition time scales based on knowledge of temperature, pressure, and composition of the combustible mixture. The work advances understanding of biofuels combustion by characterizing ignition properties of promising fuel additives and the effects of fuel blend on ignition. The resulting experimental data sets are useful for validating existing and future kinetic models. The combined models will allow for better insight into the combustion chemistry of ignition-resistant fuels formed from blending iso-octane with iso-propanol or ETBE

Impacts of Fuel Chemical Structure and Composition on Fundamental Ignition Behavior and Autoignition Chemistry in a Motored Engine.

The autoignition characteristics of individual hydrocarbon species studied in motored engine can provide a better understanding of the autoignition process and complex fuels for homogeneous spark and compression ignition engines, whether the interest is understanding and preventing knock or controlling autoignition. In both instances, there is a critical need to comprehend how fuel molecular structure either retards or promotes autoignition reactivity. This understanding ultimately contributes to the development of kinetic mechanisms, which are needed for simulation of reacting flows and autoignition processes. For this reason, the dissertation discusses autoignition data on i) three pentane isomers (n-pentane, neo-pentane and iso-pentane), ii) ethyl-cycloahexane and its two isomers (1,3-dimethyl-cyclohexane and 1,2-dimethyl-cyclohexane), and iii) diisobutylene in primary reference fuels. looking for their chemical structural impacts on the ignition process. Particularly for exploring the low and intermediate temperature regions, the motored variable compression ratio engine, developed from a Cooperative Fuel Research (CFR) Octane Rating engine, provided a good platform. Analyses of the stable intermediates in the CFR engine exhaust at various end of compression pressures and temperatures can help to identify reaction pathways through which different compounds prefer to autoignite. The approach of those studies is to conduct a systematic investigation of the autoignition, which can provide useful input for qualitative and semi-quantitative validation of kinetic mechanisms for oxidation of target chemical compounds. Finally, the dissertation is further extended to an experimental validation of jet aviation fuel surrogates, potentially emulating a series of physical and chemical ignition processes in diesel engines, with an emphasis on the needs for detailed auto-ignition characteristics of various individual hydrocarbon species.PhDChemical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/133374/1/kangdo_1.pd

Experimental investigations on controlled auto-ignition combustion in a four-stroke gasoline engine

This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University.The effects of air and exhaust gas dilution on the CAI combustion of a range of fuels including three gasoline compositions, four primary reference fuels, and two alcohols are experimentally investigated using a single cylinder research engine. Two of the three gasolines tested are manufactured from standard gasoline during engine operation by a novel fuel system, designed to improve the performance of both controlled autoignition and spark ignition engines. A series of experimental tests are performed to establish the satisfactory combined air and exhaust gas dilution regions for each fuel. Detailed in-cylinder pressure and exhaust gas speciation measurements are taken, and the fuels are compared and contrasted for their performance in terms of power output, fuel consumption, and harmful exhaust emissions. Results show that alcohol fuels are superior to hydrocarbon fuels for controlled autoignition combustion because their autoignition characteristics are less affected by the presence of exhaust gas species. Furthermore, the timing of autoignition is shown to be of minor importance for achieving efficient and stable controlled autoignition combustion, contrary to widely held beliefs. In addition, the novel fuel system is developed and commissioned for use on a single cylinder research engine operating with a spark ignition system. The two gasoline fuels produced by the system are evaluated individually for their knocking combustion characteristics over a range of compression ratios and spark advances. Results from these tests indicate that the fuel system used in conjunction with a specially modified production engine may allow the normal compression ratio of that engine to be increased by up to 1.0, increasing its efficiency.Financial support obtained from Ford Motor Company

Prediction of auto-ignition temperatures and delays for gas turbine applications

International audienceGas turbines burn a large variety of gaseous fuels under elevated pressure and temperature conditions. During transient operations, variable gas/air mixtures are involved in the gas piping system. In order to predict the risk of auto-ignition events and ensure a safe operation of gas turbines, it is of the essence to know the lowest temperature at which spontaneous ignition of fuels may happen. Experimental auto-ignition data of hydrocarbon–air mixtures at elevated pressures are scarce and often not applicable in specific industrial conditions. Auto-ignition temperature (AIT) data correspond to temperature ranges in which fuels display an incipient reactivity, with timescales amounting in seconds or even in minutes instead of milliseconds in flames. In these conditions, the critical reactions are most often different from the ones governing the reactivity in a flame or in high temperature ignition. Some of the critical paths for AIT are similar to those encountered in slow oxidation. Therefore, the main available kinetic models that have been developed for fast combustion are unfortunately unable to represent properly these low temperature processes. A numerical approach addressing the influence of process conditions on the minimum AIT of different fuel/air mixtures has been developed. Several chemical models available in the literature have been tested, in order to identify the most robust ones. Based on previous works of our group, a model has been developed, which offers a fair reconciliation between experimental and calculated AIT data through a wide range of fuel compositions. This model has been validated against experimental auto-ignition delay times corresponding to high temperature in order to ensure its relevance not only for AIT aspects but also for the reactivity of gaseous fuels over the wide range of gas turbine operation conditions. In addition, the AITs of methane, of pure light alkanes, and of various blends representative of several natural gas and process-derived fuels were extensively covered. In particular, among alternative gas turbine fuels, hydrogen-rich gases are called to play an increasing part in the future so that their ignition characteristics have been addressed with particular care. Natural gas enriched with hydrogen, and different syngas fuels have been studied. AIT values have been evaluated in function of the equivalence ratio and pressure. All the results obtained have been fitted by means of a practical mathematical expression. The overall study leads to a simple correlation of AIT versus equivalence ratio/pressure

Prediction of Auto-Ignition Temperatures and Delays for Gas Turbine Applications

International audienceGas turbines burn a large variety of gaseous fuels under elevated pressure and temperature conditions. During transient operations like maintenance, start-ups or fuel transfers, variable gas/air mixtures are involved in the gas piping system. Therefore, in order to predict the risk of auto-ignition events and ensure a safe and optimal operation of gas turbines, it is of the essence to know the lowest temperature at which spontaneous ignition of fuels may happen. Experimental auto-ignition data of hydrocarbon-air mixtures at elevated pressures are scarce and often not applicable in specific industrial conditions. AIT data correspond to temperature ranges in which fuels display an incipient reactivity, with time scales amounting in seconds or even in minutes instead of milliseconds in flames. In these conditions, the critical reactions are most often different from the ones governing the reactivity in a flame or in high temperature ignition. Some of the critical paths for AIT, especially those involving peroxy radicals, are similar to those encountered in slow oxidation. Therefore, the main available kinetic models that have been developed for fast combustion, are unfortunately unable to represent properly these low temperature processes.In this context, a numerical approach addressing the influence of process conditions on the minimum auto-ignition temperature of different fuel/air mixtures has been developed. For that purpose, several chemical models available in the literature have been tested, in order to identify the most robust ones. Based on previous works of our group, a model covering a large temperature range has been developed, which offers a fair reconciliation between experimental and calculated AIT data through a wide range of fuel compositions. This model has been validated against experimental auto-ignition delay times (AID) corresponding to high temperature in order to ensure its relevance not only for AIT aspects but also for the reactivity of gaseous fuels over the wide range of gas turbine operation conditions. In addition, the AITs of methane, of pure light alkanes and of various blends representative of several natural gas and process-derived fuels were extensively covered. In particular, among alternative gas turbine fuels, hydrogen-rich gases are called to play an increasing part in the future so that their ignition characteristics have been addressed with particular care. Natural gas enriched with hydrogen, and different CO/H2 syngas fuels originating from a blast furnace (BFG) have namely been studied. Globally, the individual species covered are: H2, CO, CO2, N2, CH4, C2H6, C3H8, C4H10, and C5H12. AIT values have been evaluated in function of the equivalence ratio and pressure. All the results obtained have been fitted by means of a practical mathematical expression. The overall study leads to a simple correlation of AIT versus equivalence ratio/pressure that may be of fruitful use for the engineering community