Development of Isopentanol Reaction Mechanism Reproducing Autoignition Character at High and Low Temperatures Taku Tsujimura,* ,† William J. Pitz, ‡ Fiona Gillespie, § Henry J. Curran, § Bryan W. Weber, ∥ Yu Zhang, ∥ and Chih-Jen Sung ∥ † National Institute of Advanced Industrial Science and Technology, 1-2-1 Namiki, Tsukuba, Ibaraki 305-8564, Japan ‡ Lawrence Livermore National Laboratory, 7000 East Avenue, Livermore, California 94551, United States § National University of Ireland, Galway, University Road, Galway, Ireland ∥ The University of Connecticut, 191 Auditorium Road, Unit 3139, Storrs, Connecticut 06269−3139, United States ABSTRACT: Isopentanol is one of a range of next-generation biofuels that can be produced by advanced biochemical production routes (i.e., genetically engineered metabolic pathways). Isopentanol is a C 5 branched alcohol and is also called 3-methyl-1-butanol. In comparison with the most frequently studied ethanol, the molecular structure of isopentanol has a longer carbon chain and includes a methyl branch. The volumetric energy density of isopentanol is over 30% higher than ethanol. Therefore, isopentanol has the capability to be a better alternative than ethanol to gasoline. In this study, a detailed chemical kinetic model for isopentanol has been developed focusing on autoignition characteristics over a wide range of temperatures. The isopentanol model developed in this study includes high- and low-temperature chemistry. In the isopentanol model, high- temperature chemistry is based on a reaction model for butanol isomers whose reaction paths are quite similar to isopentanol. The low-temperature chemistry is based on a reaction model for isooctane which is a branched molecular structure similar to isopentanol. The model includes a new reaction mechanism for a concerted HO 2 elimination, a process recently examined by da Silva et al. for ethanol (J. Phys. Chem. A 2009, 113, 8923). In addition, important reaction mechanisms relevant to low- temperature chemistry were considered in this model. The authors conducted experiments with a shock-tube and a rapid compression machine to evaluate and improve accuracies of this model. The experiments were carried out over a wide range of temperatures, pressures, and equivalence ratios (652−1457 K, 0.7−2.3 MPa, and 0.5−2.0, respectively). Excellent agreement between model calculations and experimental data was achieved under most conditions. Therefore, it is believed that the isopentanol model developed in this study is useful for prediction and analysis of combustion performance involving autoignition processes such as a homogeneous charge compression ignition. 1. INTRODUCTION Bioderived alcohols are promising gasoline substitutes for conventional spark ignition engines and for advanced homo- geneous charge compression ignition (HCCI) engines. Ethanol is the most popular bioderived alcohol which has been used in many countries as a gasoline substitute in blends and stand- alone. If a large amount of ethanol is blended in gasoline, some modifications in materials of fuel pipes, tank, hoses, etc., and in compatibility of engine controls, are required due to the low volumetric energy density (35% less than gasoline), high O/C ratio, and high hygroscopicity of ethanol. In addition, severe problems can occur due to ethanol’s significantly higher solu- bility into water which makes it difficult to use existing pipelines and infrastructure. On the other hand, a great increase in vapor pressure can occur when a small amount of ethanol is blended into gasoline (∼E10). Compared to ethanol, higher alcohols have several advan- tages because of their higher energy content, lower hygrosco- picity, and lower corrosivity. The higher alcohols can be produced from several feed stocks either directly or via gasification. 1−3 A genetically engineered metabolic pathway has been established to produce C 4 −C 5 alcohols without the traditional fermenta- tion route. Such advanced biochemical production routes for next-generation biofuels promise production of a great amount of bioderived fuels which would be more compatible with existing fuel distribution and combustion infrastructure. 4 Isopentanol, also known as 3-methyl-1-butanol, is a branched alcohol with 5 carbon atoms, and is one of the targets at the Department Of Energy (DOE) Joint BioEnergy Institute in the U.S. 2,3 Isopentanol has some advantages over ethanol as a gaso- line substitute since isopentanol has a greater similarity to gasoline in physiochemical properties. For example, isopentanol has much lower miscibility in water, and has a higher volu- metric energy density (over 30% higher than ethanol, and also 2% higher than n-butanol). Despite the status of isopentanol as a prospective bioderived fuel, to the authors’ knowledge, the combustion fundamentals of isopentanol have not been signi- ficantly studied. Yang et al. 5 have investigated combustion fundamentals of isopentanol in their HCCI engine. They found that, similarly to ethanol, isopentanol lacks two-stage ignition for typical HCCI operating conditions despite the fact that iso- pentanol has higher HCCI reactivity than gasoline or ethanol. Isopentanol did not show two-stage ignition even if the engine ran at very low engine speed (350 rpm) with considerable Received: May 21, 2012 Revised: July 15, 2012 Published: July 17, 2012 Article pubs.acs.org/EF © 2012 American Chemical Society 4871 dx.doi.org/10.1021/ef300879k | Energy Fuels 2012, 26, 4871−4886