Autoignition Chemistry of Gasoline Surrogates Relevant to HCCI Operating Conditions

University Of Connecticut, Storrs CT

Investigators

Abstract

0932559 Sung Homogeneous charge compression ignition (HCCI) combustion has received much attention during the past few years as a cost-effective means of increasing the fuel economy of gasoline engines. HCCI engines offer the potential for 10 to 15% improvement in fuel economy and dramatic reductions in NOx emissions as compared to today's conventional SI engines. While the potential benefits of HCCI combustion are great, this combustion mode has several practical development issues that must be solved before it can be implemented. One of the goals of this project is to develop surrogate fuels made from a small number (less than 10) of pure hydrocarbon components that closely mimics the global ignition characteristics of gasoline at conditions representative of HCCI combustion. The use of surrogate fuels is a viable approach to make the development of chemical kinetic mechanisms for practical fuels tractable. This proposed research aims to conduct kinetic investigation of surrogate fuels relevant to HCCI operating conditions and provide benchmark experimental data of high fidelity that will be used to validate the predictive capability of chemical kinetic models. The main focus of this three-year program will be to experimentally determine the ignition characteristics of neat and blended components for gasoline surrogate fuels using a uniquely designed rapid compression machine. Experimental conditions will cover the compressed pressures of 10-50 bar and charge temperatures of 650-1100 K. Based on the measured pressure traces, information about the delay times of the first and second stage ignition, heat release associated with the first stage ignition, and the fuel burning rate can be obtained. The neat fuel components of interest include n-heptane, iso-octane, toluene, 1-pentene, and methylcyclohexane, while experiments will be also conducted using research-grade gasoline. Experimental efforts will first focus on the investigations of each of these five components in neat form over a range of pressures, temperatures, air-to-fuel ratios, and dilution levels. Subsequently, these neat hydrocarbons will be blended into test fuels, including binary, ternary, and higher-order blends, which will be evaluated to determine if the ignition characteristics match that of a fully blended gasoline. With the availability of benchmark experimental data in a well-defined configuration, the fuel kinetics can be systematically studied, which represents an important step towards the development of robust detailed and reduced chemical mechanisms for gasoline surrogate fuels. For comprehensive kinetic modeling, literature experimental data from shock tubes, flow reactors, and flames will also be included and considered. It is recognized that the kinetics of these neat fuels is rather complex and not yet properly understood. Significant advances in terms of the availability of critical experimental data and kinetic understandings are expected from this proposed work. This research program will provide an invaluable experimental database and chemical kinetic models for gasoline surrogate fuels. These results are critical for the development of successful HCCI engines. Enhanced understanding of gasoline surrogate fuels through this research will help in overcoming R&D barriers to the development of HCCI engines by making reliable predictions and explorations through numerical simulations. Estimates show that if HCCI technology can be successfully implemented starting from year 2010, large savings in the US demand for gasoline in the transportation sector are possible. Furthermore, the research conducted will directly contribute to an improvement in the learning experience of undergraduate and graduate students. With active participation in cutting-edge combustion research, talented students can be attracted to retain in science/engineering areas and be well prepared to meet challenges in the field of clean and efficient energy utilization.