An understanding of the ignition and oxidation characteristics of propanol, as well as other alcohols, is important toward the development and design of combustion engines that can effectively utilize bioderived and bioblended fuels. Building upon a database for “first-generation” alcohols including methanol and ethanol, the ignition characteristics of the two isomers of propanol (n-propanol and iso-propanol) have been studied in a shock tube. Ignition delay times for propanol/oxygen/argon mixtures have been measured behind reflected shock waves at temperatures ranging from approximately 1350 to 2000 K and a pressure of 1 atm. Equivalence ratios of 0.5, 1.0, and 2.0 have been used. Pressure measurements and CH* emissions were used to determine ignition delay times. The influences of equivalence ratio, temperature, and mixture strength on ignition delay have been characterized and compared to the behavior seen with a newly developed detailed kinetic mechanism. The overall trends are captured fairly well by the mechanism, which include a greater level of reactivity for the n-propanol mixtures relative to iso-propanol at the conditions used in this study.

Rapid compression machines (RCMs) are widely-used to acquire experimental insights into fuel autoignition and pollutant formation chemistry, especially at conditions relevant to current and future combustion technologies. RCM studies emphasize important experimental regimes, characterized by lowto intermediate-temperatures (600-1200 K) and moderate to high pressures (5-80 bar). At these conditions, which are directly relevant to modern combustion schemes including low temperature combustion (LTC) for internal combustion engines and dry low emissions (DLE) for gas turbine engines, combustion chemistry exhibits complex and experimentally challenging behaviors such as the chemistry attributed to cool flame behavior and the negative temperature coefficient regime. Challenges for studying this regime include that experimental observations can be more sensitive to coupled physicalchemical processes leading to phenomena such as mixed deflagrative/autoignitive combustion. Experimental strategies which leverage the strengths of RCMs have been developed in recent years to make RCMs particularly well suited for elucidating LTC and DLE chemistry, as well as convolved physicalchemical processes. Specifically, this work presents a review of experimental and computational efforts applying RCMs to study autoignition phenomena, and the insights gained through these efforts. A brief history of RCM development is presented towards the steady improvement in design, characterization, instrumentation and data analysis. Novel experimental approaches and measurement techniques, coordinated with computational methods are described which have expanded the utility of RCMs beyond empirical studies of explosion limits to increasingly detailed understanding of autoignition chemistry and the role of physical-chemical interactions. Fundamental insight into the autoignition chemistry of specific fuels is described, demonstrating the extent of knowledge of low-temperature chemistry derived from RCM studies, from simple hydrocarbons to multi-component blends and full-boiling range fuels. Emerging needs and further opportunities are suggested, including investigations of under-explored fuels and the implementation of increasingly higher fidelity diagnostics.

Sandia National Laboratories has been investigating a new, integrated approach to generating electricity with ultra low emissions and very high efficiency for low power (30 kW) applications such as hybrid vehicles and portable generators. Our approach utilizes a free piston in a double-ended cylinder. Combustion occurs alternately at each cylinder end, with intake/exhaust processes accomplished through a two stroke cycle. A linear alternator is mounted in the center section of the cylinder, serving to both generate useful electrical power and to control the compression ratio by varying the rate of electrical generation. Thus, a mechanically simple geometry results in an electronically controlled variable compression ratio configuration. The capability of the homogeneous charge compression ignition combustion process employed in this engine with regards to reduced emissions and improved thermal efficiency has been investigated using a rapid compression expansion machine. Eight different fuels, including propane, natural gas, hydrogen, methanol, n-pentane, hexane, n-heptane, and isooctane have been used at low equivalence ratio (φ ~ 0.35) and initial temperatures of 25°C, 50°C and 70°C. The results indicate that the cycle thermal efficiency can be significantly improved (56% measured) relative to current combustion systems, while low NO x emissions are possible (<10 PPM). HC and CO emissions must be controlled through some aftertreatment technology. The primary cause of

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