Gregory R. Magoon

Database of Small Molecule Thermochemistry for Combustion

High-accuracy ab initio thermochemistry is presented for 219 small molecules relevant in combustion chemistry, including many radical, biradical, and triplet species. These values are critical for accurate kinetic modeling. The RQCISD(T)/cc-PV∞QZ//B3LYP/6-311++G(d,p) method was used to compute the electronic energies. A bond additivity correction for this method has been developed to remove systematic errors in the enthalpy calculations, using the Active Thermochemical Tables as reference values. On the basis of comparison with the benchmark data, the 3σ uncertainty in the standard-state heat of formation is 0.9 kcal/mol, or within chemical accuracy. An uncertainty analysis is presented for the entropy and heat capacity. In many cases, the present values are the most accurate and comprehensive numbers available. The present work is compared to several published databases. In some cases, there are large discrepancies and errors in published databases; the present work helps to resolve these problems.

Use of electrochemical sensors for measurement of air pollution: correcting interference response and validating measurements

The environments in which we live, work, and play are subject to enormous variability in air pollutant concentrations. To adequately characterize air quality (AQ), measurements must be fast (real time), scalable, and reliable (with known accuracy, precision, and stability over time). Lower-cost air-quality-sensor technologies offer new opportunities for fast and distributed measurements, but a persistent characterization gap remains when it comes to evaluating sensor performance under realistic environmental sampling conditions. This limits our ability to inform the public about pollution sources and inspire policy makers to address environmental justice issues related to air quality. In this paper, initial results obtained with a recently developed lower-cost air-quality-sensor system are reported. In this project, data were acquired with the ARISense integrated sensor package over a 4.5-month time interval during which the sensor system was co-located with a state-operated (Massachusetts, USA) air quality monitoring station equipped with reference instrumentation measuring the same pollutant species. This paper focuses on validating electrochemical (EC) sensor measurements of CO, NO, NO2, and O3 at an urban neighborhood site with pollutant concentration ranges (parts per billion by volume, ppb; 5 min averages, ±1σ): [CO]= 231± 116 ppb (spanning 84–1706 ppb), [NO]= 6.1± 11.5 ppb (spanning 0–209 ppb), [NO2]= 11.7± 8.3 ppb (spanning 0–71 ppb), and [O3]= 23.2± 12.5 ppb (spanning 0–99 ppb). Through the use of high-dimensional model representation (HDMR), we show that interference effects derived from the variable ambient gas concentration mix and changing environmental conditions over three seasons (sensor flow-cell temperature= 23.4± 8.5 C, spanning 4.1 to 45.2 C; and relative humidity= 50.1± 15.3 %, spanning 9.8–79.9 %) can be effectively modeled for the Alphasense CO-B4, NO-B4, NO2B43F, and Ox-B421 sensors, yielding (5 min average) root mean square errors (RMSE) of 39.2, 4.52, 4.56, and 9.71 ppb, respectively. Our results substantiate the potential for distributed air pollution measurements that could be enabled with these sensors.

Updating Our Understanding of JP-10 Decomposition Chemistry: A Detailed JP-10 Combustion Mechanism Constructed Using RMG - an Automatic Reaction Mechanism Generator

We are applying Reaction Mechanism Generator (RMG) to detailed and comprehensive characterization of JP-10 combustion chemistry. JP-10 is a large synthetic fuel with complex high temperature decomposition chemistry for which detailed characterization has been considered intractable; and RMG is a computer program that we developed for automatic construction of predictive kinetic models. In this paper, we present initial results from applying RMG to JP-10 combustion. After considering over 25,000 possible species and more than 1 million possible reactions, we have developed a highly detailed JP-10 combustion mechanism that currently consists of 317 chemical species and 7,715 elementary reactions. Comparisons against existing mechanisms and experimental data in published literature reveal that this RMG-constructed mechanism establishes a new state of the art in JP-10 combustion modeling: ignition delay predictions accurately reproduce experimental observations (to our knowledge, the first detailed mechanism to accomplish this); and our mechanism provides the first detailed insight into the high temperature initial decomposition chemistry of JP-10 in the presence of oxygen, particularly down to C5 hydrocarbons. We are also developing transport property estimates for all species in the mechanism. The final result of this effort will be an experimentally validated comprehensive JP-10 combustion mechanism containing all parameters necessary for application in reacting flow simulations.