Experiments and Modeling of the Autoignition of Methyl-Cyclohexane at High Pressure

The autoignition delays of mixtures of methyl-cyclohexane (MCH), oxygen, nitrogen, and argon have been studied in a heated rapid compression machine under the conditions $P_C$ = 50 bar, $T_C$ = 690 - 910K. Three different mixture compositions were studied, with equivalence ratios ranging from $\phi$ = 0.5 - 1.5. The trends of the ignition delay measured at 50 bar were similar to the trends measured in earlier experiments at $P_C$ = 15.1 and 25.5 bar. The experimentally measured ignition delays were compared to a newly updated chemical kinetic model for the combustion of MCH. The model has been updated to include newly calculated reaction rates for much of the low-temperature chemistry. The agreement between the experiments and the model was substantially improved compared to a previous version of the model. Nevertheless, despite the encouraging improvements, work continues on further advances, e.g. in improving predictions of the first stage ignition delays.Comment: 8 pages, 8 figures, 1 table, presented at the 8th US National Combustion Meetin

Development of a diesel surrogate for improved autoignition prediction: Methodology and detailed chemical kinetic modeling

While the surrogate fuel approach has been successfully applied to the simulation of the combustion behaviors of complex gasoline and jet fuels, its application to diesel fuels has been challenging. One of the main challenges derives from the large molecular size of the representative surrogate components necessary to simulate diesel blends, as the development of detailed chemical kinetic models and their validation becomes more complex. In this study, a new surrogate mixture that emulates the chemical and physical properties of a well-characterized diesel fuel is proposed. An optimization procedure was used to select surrogate components that can match both the physical and chemical properties of the target diesel fuel comprehensively. The surrogate fuel mixture composition was designed to have fuel properties (e.g., boiling point, cloud point, etc.) that enable its use in future diesel engine experiments. A detailed kinetic model for the surrogate fuel mixture was developed by combining well-validated sub-mechanisms of each surrogate component from Lawrence Livermore National Laboratory. The ability of the surrogate mixture and kinetic model to emulate ignition delay times was assessed by comparing the simulated results with measurements for the target diesel fuel. Comparison of the experimental and simulated ignition delay times shows that the current surrogate mixture and kinetic model well capture the autoignition response of the target diesel fuel at varying conditions of pressure, temperature, oxygen concentration, and fuel concentration. The current study is one of the first to demonstrate the efficacy of detailed chemical kinetics for diesel range fuels by assembling validated sub-mechanisms for palette compounds and successfully simulating the autoignition characteristics of a target diesel fuel. The experimental ignition delay times of diesel measured with a rapid compression machine, the surrogate mixture, and the kinetic model developed shall aid in progress of understanding diesel ignition under engine relevant conditions

Oxidation of hazardous waste in supercritical water: A comparison of modeling and experimental results for methanol destruction

Recent experiments at Sandia National Laboratories conducted in conjunction with MODEC Corporation have demonstrated successful clean- up of contaminated water in a supercritical water reactor. These experiments targeted wastes of interest to Department of Energy production facilities. In this paper we present modeling and experimental results for a surrogate waste containing 98% water, 2% methanol, and parts per million of chlorinated hydrocarbons and laser dyes. Our initial modeling results consider only methanol and water. Experimental data are available for inlet and outlet conditions and axial temperature profiles along the outside reactor wall. The purpose of our model is to study the chemical and physical processes inside the reactor. We are particularly interested in the parameters that control the location of the reaction zone. The laboratory-scale reactor operates at 25 MPa., between 300 K and 900 K; it is modeled as a plug-flow reactor with a specified temperature profile. We use Chemkin Real-Gas to calculate mixture density, with the Peng-Robinson equation of state. The elementary reaction set for methanol oxidation and reactions of other C{sub 1} and C{sub 2} hydrocarbons is based on previous models for gas-phase kinetics. Results from our calculations show that the methanol is 99.9% destroyed at 1/3 the total reactor length. Although we were not able to measure composition of the fluid inside the experimental reactor, this prediction occurs near the location of the highest reactor temperature. This indicates that the chemical reaction is triggered by thermal effects, not kinetic rates. Results from ideal-gas calculations show nearly identical chemical profiles inside the reactor in dimensionless distance. However, reactor residence times are overpredicted by nearly 150% using an ideal-gas assumption. Our results indicate that this oxidation process can be successfully modeled using gas-phase chemical mechanisms. 23 refs., 8 figs

Experimental and Kinetic Modeling Study of Extinction and Ignition of Methyl Decanoate in Laminar Nonpremixed Flows

Methyl decanoate is a large methyl ester that can be used as a surrogate for biodiesel. In this experimental and computational study, the combustion of methyl decanoate is investigated in nonpremixed, nonuniform flows. Experiments are performed employing the counterflow configuration with a fuel stream made up of vaporized methyl decanoate and nitrogen, and an oxidizer stream of air. The mass fraction of fuel in the fuel stream is measured as a function of the strain rate at extinction, and critical conditions of ignition are measured in terms of the temperature of the oxidizer stream as a function of the strain rate. It is not possible to use a fully detailed mechanism for methyl decanoate to simulate the counterflow flames because the number of species and reactions is too large to employ with current flame codes and computer resources. Therefore a skeletal mechanism was deduced from a detailed mechanism of 8555 elementary reactions and 3036 species using 'directed relation graph' method. This skeletal mechanism has only 713 elementary reactions and 125 species. Critical conditions of ignition were calculated using this skeletal mechanism and are found to agree well with experimental data. The predicted strain rate at extinction is found to be lower than the measurements. In general, the methyl decanoate mechanism provides a realistic kinetic tool for simulation of biodiesel fuels

Development of the RIOT Web Service and Information Technologies to enable mechanism reduction for HCCI simulations.

Abstract. New approaches are being explored to facilitate multidisciplinary collaborative research of Homogenous Charge Compression Ignition (HCCI) combustion processes. In this paper, collaborative sharing of the Range Identification and Optimization Toolkit (RIOT) and related data and models is discussed. RIOT is a developmental approach to reduce the computational of detailed chemical kinetic mechanisms, enabling their use in modeling kinetically controlled combustion applications such as HCCI. These approaches are being developed and piloted as a part of the Collaboratory for Multiscale Chemical Sciences (CMCS) project. The capabilities of the RIOT code are shared through a portlet in the CMCS portal that allows easy specification and processing of RIOT inputs, remote execution of RIOT, tracking of data pedigree, and translation of RIOT outputs to a table view and to a commonly-used mechanism format. Introduction The urgent need for high-efficiency, low-emission energy utilization technologies for transportation, power generation, and manufacturing processes presents difficult challenges to the combustion research community. The needed predictive understanding requires systematic knowledge across the full range of physical scales involved in combustion processes -from the properties and interactions of individual molecules to the dynamics and products of turbulent multi-phase reacting flows. Innovative experimental techniques and computational approaches are revolutionizing the rate at which chemical science research can produce the new information necessary to advance our combustion knowledge. But the increased volume and complexity of this information often makes it even more difficult to derive the systems-level knowledge we need. Combustion researchers have responded by forming interdisciplinary communities intent on sharing information and coordinating research priorities. Such efforts face many barriers, however, including lack of data accessibility and interoperability, missing metadata and pedigree information, efficient approaches for sharing data and analysis tools, and the challenges of working together across geography, disciplines, and a very diverse spectrum of applications and funding. This challenge is especially difficult for those developing, sharing and/or using detailed chemical models of combustion to treat the oxidation of practical fuels. This is a very complex problem, and the development of new chemistry models requires a series of steps that involve acquiring and keeping track of a large amount of data and its pedigree. Also, this data is developed using a diverse range of codes and experiments spanning ab initio chemistry codes, laboratory kinetics and flame experiments, all the way to reacting flow simulations on massively parallel computers. Each of these processes typically requires different data formats, and often the data and/or analysis codes are only accessible by personally contacting the creator. Chemical models are usually shared in a legacy file format, such as Chemki

The effect of oxygenate molecular structure on soot production in direct-injection diesel engines.

A combined experimental and kinetic modeling study of soot formation in diesel engine combustion has been used to study the addition of oxygenated species to diesel fuel to reduce soot emissions. This work indicates that the primary role of oxygen atoms in the fuel mixture is to reduce the levels of carbon atoms available for soot formation by fixing them in the form of CO or COz. When the structure of the oxygenate leads to prompt and direct formation of CO2, the oxygenate is less effective in reducing soot production than in cases when all fuel-bound 0 atoms produce only CO. The kinetic and molecular structure principles leading to this conclusion are described