Autoignition of natural gas fuels with ethane and propane additives at low to intermediate temperature

Advanced combustion systems are designed to achieve lower pollutant emissions, higher efficiencies and greater fuel flexibility. However, more uniform fuel/air mixing, higher operational pressure and temperature of these systems increase the propensity to a few critical issues such as autoignition. As an important characteristic of a fuel, autoignition is affected by its operational parameters (such as temperature, pressure, and equivalence ratio) and fuel composition. Natural gas varies greatly in its fuel compositions due to its origin and handling. Although the primary constituent in natural gas is methane (CH 4) and higher hydrocarbons (hydrocarbons with two or more carbon atoms) count for only a small fraction in natural gas, they play a critical role in characterizing the autoignition of natural gas. This dissertation studies the autoignition of natural gas fuels with ethane and propane additives at low to intermediate temperature (773--1573 K).;To effectively and efficiently study autoignition of natural gas over a wide range of operational conditions and fuel compositions, statistical design of experiments (DOEx) methodologies are utilized to design test matrices, which are implemented with simulation data obtained from detailed chemical kinetics modeling using existing validated detailed chemical kinetics mechanisms.;A series of factorial studies are first conducted to identify critical impacting factors of autoignition delay times of natural gas fuels at different temperatures. In both lower and temperature ranges, higher hydrocarbon additives are found to play important while distinct roles while equivalence ration is found to have little effect.;To quantitatively characterize the autoignition characteristics of natural gas, correlations of autoignition temperature and autoignition delay time as a function of operational parameter and fuel composition are developed based on chemical kinetics simulation results. The correlations then are evaluated and compared to existing correlations. Furthermore, temperature sensitivity analysis is conducted to reveal the effects of higher hydrocarbon additives on autoignition of natural gas fuels and to identify the most important reactions of the detailed chemical kinetics mechanisms in affecting autoignition. In addition, the general procedures and methodologies that are outlined can be used to efficiently assess and compare the autoignition characteristics of different fuel under different conditions in either experimental or simulation studies.