Ninth Symposium (International) on Combustion

In this study, a novel approach was developed to formulate surrogate fuels having characteristics that are representative of diesel fuels produced from real-world refinery streams. Because diesel fuels typically consist of hundreds of compounds, it is difficult to conclusively determine the effects of fuel composition on combustion properties. Surrogate fuels, being simpler representations of these practical fuels, are of interest because they can provide a better understanding of fundamental fuel-composition and property effects on combustion and emissions-formation processes in internal-combustion engines. In addition, the application of surrogate fuels in numerical simulations with accurate vaporization, mixing, and combustion models could revolutionize future engine designs by enabling computational optimization for evolving real fuels. Dependable computational design would not only improve engine function, it would do so at significant cost savings relative to current optimization strategies that rel...

/pdf/methodology-for-formulating-diesel-surrogate-fuels-with-fayk44gbfz.pdf

Methodology for Formulating Diesel Surrogate Fuels with Accurate Compositional, Ignition-Quality, and Volatility Characteristics

The demand for transport energy is increasing, but this increase is heavily skewed toward heavier fuels such as diesel and jet fuel while the demand for gasoline might decrease. As spark-ignition engines develop to become more efficient, abnormal combustion such as knock and preignition will become more likely. High antiknock quality fuels, those with high research octane number and preferably low motor octane number, will enable future spark-ignition engines to reach their full potential. Higher fuel antiknock quality is also likely to mitigate “superknock” resulting from preignition—an abnormal combustion problem in turbocharged spark-ignition engines. In many parts of the world, fuel antiknock specifications are set on the assumption that higher motor octane number contributes to increased knock resistance. Specifications for fuel antiknock quality have a great impact on fuels manufacture and will need to be revised as this mismatch between existing specifications and engine requirements widens. The pr...

The outlook for fuels for internal combustion engines

Homogeneous charge compression ignition (HCCI) engine uses a relatively new mode of combustion technology. In principle, there is no spark plug or injector to assist the combustion, and the combustion auto-ignites in multiple spots once the mixture has reached its chemical activation energy. The challenges in developing HCCI engines are the difficulties in: controlling the auto-ignition of the mixture and the heat release rate at high load operations, achieving a cold start, meeting emission standards and controlling knock. At low engine speeds, early auto-ignition can occur, possibly leading to knocking, while late auto-ignition at high engine speeds will make HCCI susceptible to misfire. Hydrogen greatly reduces emissions levels but with reduced power. However, when hydrogen is combined with diesel in dual-fuel mode, low NOx, CO and particulate matter (PM) emissions levels can be achieved, and engine efficiency can be increased by 13–16%. Numerical methods are commonly used to predict HCCI engines' performance (i.e. emissions levels, brake thermal efficiency and combustion phasing), which is cost-effective compared to solely relying on experimentation. The multi-zone method promises better simulation results compared to the single-zone model by combining detailed chemical kinetics with simplified 3D modeling so that turbulence and inhomogeneity in the mixture are considered; good agreement between simulations and experiments have been achieved. Specific strategies used in the experimental method (e.g. fuel additives, inlet air heating, inlet air pressurizing, exhaust gas recirculation (EGR) and injection methods), and numerical method (e.g. single-zone and multi-zone models, mixing model, turbulence model and multi-dimensional model), and other issues associated with HCCI engines are discussed in this paper.

/pdf/a-review-of-hydrogen-and-natural-gas-addition-in-diesel-hcci-uzg24lg225.pdf

A review of hydrogen and natural gas addition in diesel HCCI engines

Combustion machine learning: Principles, progress and prospects

Efficient Simulation of Diesel Engine Combustion Using Realistic Chemical Kinetics in CFD

Validation Studies of a Detailed Kinetics Mechanism for Diesel and Gasoline Surrogate Fuels

A method has been developed in which the flow field predicted by Computational Fluid Dynamics (CFD) is automatically condensed into an Equivalent Reactor Network (ERN), composed of well stirred reactors, allowing rapid and accurate analysis of emissions. This paper presents the effectiveness of utilizing an ERN that is a direct abstraction of the computational flow field for combustion analysis. The CFD results are divided into reactors using various filters on flow-field variables to construct an ERN that represents the 3-D combustor flow field and flame structure. Detailed kinetics can then be used in ERN simulations to analyze effects of fuel composition and operating condition on emissions. The technique is applied to a commercial industrial gas turbine combustor fuel injector and compared against experimental emissions results. Sensitivity of emissions predictions to different parameters in the network extraction is also presented. Parameter variations in fuel flow rate are applied to the ERN to obtain relative impacts of fuel-air ratio on the emissions of NOx without requiring new CFD solutions. This automatic approach has been found to reduce the time required to construct and analyze flow field derived ERNs with detailed chemistry by 90%. A local calculation of Damkohler number, important for stability analysis, is also presented. This calculation also uses abstracted information from the CFD flow field and detailed-kinetics simulations for more accurate, cost-effective analysis.Copyright © 2009 by ASME

Flow Field Derived Equivalent Reactor Networks for Accurate Chemistry Simulation in Gas Turbine Combustors

Validated surrogate models have been developed for two Fisher-Tropsch (F-T) fuels. The models started with a systematic approach to determine an appropriate surrogate fuel composition specifically tailored for the two alternative jet-fuel samples. A detailed chemical kinetic mechanism has been assembled for these model surrogates starting from literature sources, and then improved to ensure self-consistency of the kinetics and thermodynamic data. This mechanism has been tested against fundamental laboratory data on auto-ignition times, laminar flame-speeds, extinction strain rates, and NOx emissions. Literature data used to validate the mechanism include both the individual surrogate-fuel components and actual F-T fuel samples where available. As part of the validation, simulations were performed for a wide variety of experimental configurations, as well as a wide range of temperatures and equivalence ratios for fuel/air mixtures. Comparison of predicted surrogate-fuel behavior against data on real F-T fuel behavior also show the effectiveness of the surrogate-matching approach and the accuracy of the detailed-kinetics mechanisms. The resulting validated mechanism has been also reduced through application of automated mechanism reduction techniques to provide progressively smaller mechanisms, with different degrees of accuracy, that are reasonable for use in CFD simulations employing detailed kinetics.Copyright © 2010 by ASME

Validated F-T Fuel Surrogate Model for Simulation of Jet-Engine Combustion

Ignition timing and control, as well as predictability of engine emissions, are critical factors in advanced-engine system design. The use of detailed chemical kinetics is key to simulating ignition performance and to predicting emissions. This paper describes a collaborative and systematic effort that is underway to enable computationally efficient use of accurate kinetics in engine simulation. The collaboration is focused on building a database of chemical information and on developing a complementary set of software tools that provide efficient engine-simulation capabilities. The goal is predictive simulations that capture the detailed behavior of complex fuels, such as gasoline and diesel, under homogeneous charge compression ignition (HCCI) and related operating conditions. Since directly accounting for all of the hundreds of constituent molecules in a fuel during simulation of real-fuel combustion is intractable, we employ a “model-fuel” or surrogate-fuel approach instead. Mixtures of model-fuel molecules can be determined to adequately represent important real-fuel properties and engine-combustion characteristics. In this work, model fuel compositions are determined by matching a mixture behavior to that of the real fuel, focusing on distillation-curve characteristics, net-heating value, hydrogen-to-carbon ratio, and octane/cetane numbers. This surrogate-definition process requires detailed chemical-kinetics mechanisms for a variety of model-fuel compounds. To build such a database of model-fuel component mechanisms, we have used a combination of automatic mechanism-generation and manual mechanism-development approaches. These methods adhere to a systematic set of class-based rules in determining elementary reaction rates, as well as thermodynamic and transport properties of species. In addition, a comprehensive validation study of the mechanisms, using a wide variety of both fundamental and engine experiments, has allowed refinement of these rules and improvement of both the mechanisms’ predictions and their consistency across components. Even though model fuels have a small number of components, their detailed mechanisms contain large numbers of species (>1000) and reactions (>10000). Systematic mechanism reduction is therefore required for many engineering applications. To this end, we have also developed a package of automated mechanism-reduction techniques. In addition, we have advanced the solution algorithms used in the kinetics simulations and developed a multi-zone engine model that provides good predictions of ignition behavior and emissions. We report on selected results of this systematic approach to using detailed kinetics in engineering simulation, as well as the challenges encountered.

New Modeling Approaches Using Detailed Kinetics for Advanced Engines

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