An Improved Core Reaction Mechanism for Saturated C₀-C₄ Fuels

Accurate chemistry models are required to predict the combustion behavior of different fuels, such as synthetic gaseous fuels and liquid jet fuels. A detailed reaction mechanism contains chemistry for all the molecular components in the fuel or its surrogates. Validation studies that compare model predictions with the data from fundamental combustion experiments under well-defined conditions are least affected by the effect of transport on chemistry. Therefore they are the most reliable means for determining a reaction mechanism’s predictive capabilities. Following extensive validation studies and analysis of detailed reaction mechanisms for a wide range of hydrocarbon components reported in our previously published work (Puduppakkam et al., 2010, “Validation Studies of a Master Kinetic Mechanism for Diesel and Gasoline Surrogate Fuels,” SAE Technical Paper No. 2010-01-0545; Naik et al., 2010, “Validated F-T Fuel Surrogate Model for Simulation of Jet-Engine Combustion,” Proc. ASME Turbo Expo, Paper No. GT2010-23709; Naik et al., 2010, “Applying Detailed Kinetics to Realistic Engine Simulation: The Surrogate Blend Optimizer and Mechanism Reduction Strategies,” SAE J. Engines 3(1), pp. 241–259; Naik et al., 2010, “Modeling the Detailed Chemical Kinetics of Mutual Sensitization in the Oxidation of a Model Fuel for Gasoline and Nitric Oxide,” SAE J. Fuels Lubr. 3(1), pp. 556–566; and Puduppakkam et al., 2009, “Combustion and Emissions Modeling of an HCCI Engine Using Model Fuels,” SAE Technical Paper No. 2009-01-0669), we identified some common issues in the predictive nature of the mechanisms that are associated with inadequacies of the core (C₀-C₄) mechanism, such as inaccurate predictions of laminar flame speeds and autoignition delay times for several fuels. This core mechanism is shared by all of the mechanisms for the larger hydrocarbon components. Unlike the reaction paths for larger hydrocarbon fuels; however, reaction paths for the core chemistry do not follow prescribed reaction rate-rules. In this work, we revisit our core reaction mechanism for saturated fuels, with the goal of improving predictions for the widest range of fundamental experiments. To evaluate and validate the mechanism improvements, we performed a broad set of simulations of fundamental experiments. These experiments include measurements of ignition delay, flame speed and extinction strain rate, as well as species composition in stirred reactors, flames and flow reactors. The range of conditions covers low to high temperatures, very lean to very rich fuel-air ratios, and low to high pressures. Our core reaction mechanism contains thermochemical parameters derived from a wide variety of sources, including experimental measurements, ab initio calculations, estimation methods and systematic optimization studies. Each technique has its uncertainties and potential inaccuracies. Using a systematic approach that includes sensitivity analysis, reaction-path analysis, consideration of recent literature studies, and an attention to data consistency, we have identified key updates required for the core mechanism. These updates resulted in accurate predictions for various saturated fuels when compared to the data over a broad range of conditions. All reaction rate constants and species thermodynamics and transport parameters remain within known uncertainties and within physically reasonable bounds. Unlike most mechanisms in the literature, the mechanism developed in this work is self-consistent and contains chemistry of all saturated fuels.