Thermal Stability of Distillate Hydrocarbon Fuels

Thermal stability of fuels is expected to become a severe problem in the future due to the anticipated use of broadened specification and alternative fuels. Future fuels will have higher contents of heteroatomic species which are reactive constituents and are known to influence fuel degradation. To study the degradation chemistry of selected model fuels, n-dodecane and n-dodecane plus heteroatoms were aerated by bubbling air through the fuels amd stressed on a modified Jet Fuel Thermal Oxidation Tester facility operating at heater tube temperatures between 200 to 400 C. The resulting samples were fractionated to concentrate the soluble products and then analyzed using gas chromatographic and mass spectrometric techniques to quantify and identify the stable reaction intermediate and product specifically. Heteroatom addition showed that the major soluble products were always the same, with and without heteroatoms, but their distributions varied considerably

Spark Ignition of Monodisperse Fuel Sprays

A study of spark ignition energy requirements was conducted with a monodisperse spray system allowing independent control of droplet size, equivalent ratio, and fuel type. Minimum ignition energies were measured for n-heptane and methanol sprays characterized at the spark gap in terms of droplet diameter, equivalence ratio (number density) and extent of prevaporization. In addition to sprays, minimum ignition energies were measured for completely prevaporized mixtures of the same fuels over a range of equivalence ratios to provide data at the lower limit of droplet size. Results showed that spray ignition was enhanced with decreasing droplet size and increasing equivalence ratio over the ranges of the parameters studied. By comparing spray and prevaporized ignition results, the existence of an optimum droplet size for ignition was indicated for both fuels. Fuel volatility was seen to be a critical factor in spray ignition. The spray ignition results were analyzed using two different empirical ignition models for quiescent mixtures. Both models accurately predicted the experimental ignition energies for the majority of the spray conditions. Spray ignition was observed to be probabilistic in nature, and ignition was quantified in terms of an ignition frequency for a given spark energy. A model was developed to predict ignition frequencies based on the variation in spark energy and equivalence ratio in the spark gap. The resulting ignition frequency simulations were nearly identical to the experimentally observed values

Some observations on the effects of EGR, oxygen concentration, and engine speed on the homogeneous charge combustion of n-heptane

Paper presented at the 2004 SAE Fuels and Lubricants Meeting and Exhibition, June 2004, Toulouse, France. Retrieved 3/16/2006 from http://www.mem.drexel.edu/cnf/.NOx and soot emissions remain critical issues in diesel engines. One method to address these problems is to achieve homogeneous combustion at lower peak temperatures – the goal of research on controlled autoignition. In this paper n-heptane is used to represent a large hydrocarbon fuel and some of the effects of internal and external EGR, oxygen concentration, and engine speed on its combustion have been examined through simulation and experiment. Simulations were conducted using our existing skeletal chemical kinetic model, which combines the chemistry of the low, intermediate, and high temperature regimes. Experiments were carried out in a single cylinder, four-stroke, air cooled engine and a single cylinder, two stroke, water cooled engine. In the four-stroke engine experiments the effects of EGR were examined using heated N2 addition as a surrogate for external EGR and engine modifications to increase internal EGR. Two-stage ignition was observed in both the simulations and experiments. The modeling results indicate that the ignition times were sensitive to EGR through both thermal and chemical effects. High levels of EGR completely suppressed autoignition. The most apparent effect of oxygen concentration is a shortening of the time between the first stage and second stage ignition. The modeling shows that EGR or extra air are key factors in eliminating knock during mid-load conditions. For higher load operation knock is serious and the only way to avoid it is to control reaction timing through the use of spark ignition. The experimental and modeling results from the two-stroke engine show that autoignition can be avoided by increasing the engine speed. This appears to result from shortened reaction time at lower temperatures thereby reducing the extent of the low and intermediate temperature chemical reactivity. The two-stroke engine experiments indicate that high levels of internal EGR (obtained by increasing the engine back pressure) can enable spark ignition at lean/dilute conditions. Based on the similarity between two-stoke and four-stroke engines, spark ignition may be possible at higher load conditions using internal EGR (simultaneously keeping peak temperature lower) for four-stroke engines

2022 Roadmap on integrated quantum photonics

AbstractIntegrated photonics will play a key role in quantum systems as they grow from few-qubit prototypes to tens of thousands of qubits. The underlying optical quantum technologies can only be realized through the integration of these components onto quantum photonic integrated circuits (QPICs) with accompanying electronics. In the last decade, remarkable advances in quantum photonic integration have enabled table-top experiments to be scaled down to prototype chips with improvements in efficiency, robustness, and key performance metrics. These advances have enabled integrated quantum photonic technologies combining up to 650 optical and electrical components onto a single chip that are capable of programmable quantum information processing, chip-to-chip networking, hybrid quantum system integration, and high-speed communications. In this roadmap article, we highlight the status, current and future challenges, and emerging technologies in several key research areas in integrated quantum photonics, including photonic platforms, quantum and classical light sources, quantum frequency conversion, integrated detectors, and applications in computing, communications, and sensing. With advances in materials, photonic design architectures, fabrication and integration processes, packaging, and testing and benchmarking, in the next decade we can expect a transition from single- and few-function prototypes to large-scale integration of multi-functional and reconfigurable devices that will have a transformative impact on quantum information science and engineering

A global reaction model for the HCCI combusion process

Paper presented at the 2004 Powertrain and Fluid Systems Conference and Exhibition, October 2004, Tampa, Fla. Retrieved April 2006 from http://www.mem.drexel.edu/cnf/publications/SAE_2004-01-2950.pdfThis paper presents a new global reaction model to simulate the Homogeneous Charge Compression Ignition (HCCI) combustion process. The model utilizes seven equations and seven active species. The model includes five reactions that represent degenerate chain branching in the low temperature region, including chain propagation, termination and branching reactions and the reaction of HOOH at the second stage ignition. Two reactions govern the high temperature oxidation, to allow formation and prediction of CO, CO2, and H2O. Thermodynamic parameters were introduced through the enthalpy of formation of each species. We were able to select the rate parameters of the global model to correctly predict the autoignition delay time at constant density for n-heptane and iso-octane, including the effect of equivalence ratio. Keeping the same reactions and rate parameters, simulations were compared with measured and calculated data from our engine operating at the following conditions: speed – 750 RPM, inlet temperature – 393 K to 453 K, fuel – PRF 20, equivalence ratio - 0.4 and 0.5, and volumetric efficiency - 71% and 89%. The simulations are in good agreement with the experimental data for this initial set of runs using PRF 20, including temperature, pressure, ignition delay, combustion duration, and heat release