This chapter makes a review, in a complete methodological framework, of various global sensitivity analysis methods of model output. Numerous statistical and probabilistic tools (regression, smoothing, tests, statistical learning, Monte Carlo, …) aim at determining the model input variables which mostly contribute to an interest quantity depending on model output. This quantity can be for instance the variance of an output variable. Three kinds of methods are distinguished: the screening (coarse sorting of the most influential inputs among a large number), the measures of importance (quantitative sensitivity indices) and the deep exploration of the model behaviour (measuring the effects of inputs on their all variation range). A progressive application methodology is illustrated on a scholar application. A synthesis is given to place every method according to several axes, mainly the cost in number of model evaluations, the model complexity and the nature of brought information.

A Review on Global Sensitivity Analysis Methods

Proton-transfer reaction mass spectrometry (PTR-MS) is a technique developed almost exclusively for the detection of gaseous organic compounds in air. Volatile organic compounds (VOCs) in air have both natural and anthropogenic sources. Natural sources include the emission of organic gases by living objects, both plants and animals. A well-known example, which is discussed later in this review, is the emission of a variety of gaseous organic compounds in the breath of animals, which are released from both the digestive system and the lungs. Plants are major sources of organic gases, as is the decay of dead animal and plant matter. Subsequent photochemistry can add further compounds to the mixture. Consequently, even without contributions from humans, ambient air from the Earth’s atmosphere would consist of a complex mixture of VOCs.

Proton-transfer reaction mass spectrometry.

https://elib.dlr.de/59672/1/scientdir.pdf

Transport impacts on atmosphere and climate: Aviation

Kinetics of elementary reactions in low-temperature autoignition chemistry

A detailed chemical kinetic modeling approach is used to examine the phenomenon of suppression of sooting in diesel engines by the addition of oxygenated hydrocarbon species to the fuel. This suppression, which has been observed experimentally for a few years, is explained kinetically as a reduction in concentrations of soot precursors present in the hot products of a fuel-rich diesel ignition zone when oxygenates are included. The kinetic model is also used to show how different oxygenates, ester structures in particular, can have different soot-suppression efficiencies due to differences in the molecular structure of the oxygenated species.

/pdf/chemical-kinetic-modeling-study-of-the-effects-of-oxygenated-1rycba60jz.pdf

Chemical kinetic modeling study of the effects of oxygenated hydrocarbons on soot emissions from diesel engines.

The objective of a global sensitivity analysis is to rank the importance of the system inputs considering their uncertainty and the influence they have upon the uncertainty of the system output, ty...

Global sensitivity analysis for systems with independent and/or correlated inputs.

In April 2004, the Aerodyne Mobile Laboratory measured trace gas and particle emissions from a CFM56-2C1 high-bypass-ratio turbofan engine used to power the NASA DC-8 aircraft as part of the Aircraft Particle Emissions Experiment (APEX). This article focuses on the measured hydrocarbon species which include formaldehyde, ethylene, acetaldehyde, benzene, toluene, and several higher aromatic species. Formaldehyde and ethylene were measured by tunable-infrared-laser differential absorption spectroscopy, and the other species were measured by proton-transfer reaction mass spectroscopy. Continuous samples were taken at 1,10, and 30 m downstream of the engine-exit plane of the grounded aircraft and analyzed at a frequency of up to 1 Hz. The engine power was scanned from ground-idle up to takeoff power, and three fuel types (a baseline JP-8, a high-aromatic fuel, and a high-sulfur fuel) were investigated. Fuel type and plume age were shown to have only a minor impact on hydrocarbon emissions within the ranges studied in this experiment. However, ambient temperature was shown to have a substantial effect on these emissions. The sum of these speciated measurements agreed favorably with separate measurements of the total hydrocarbon emissions by flame ionization. The fast time response of the speciated measurements revealed interesting variability and transient behavior on a several-second timescale.

Chemical Speciation of Hydrocarbon Emissions from a Commercial Aircraft Engine

Approximately 15 million dry tons of food waste is produced annually in the United States (USA), and 92% of this waste is disposed of in landfills where it decomposes to produce greenhouse gases and water pollution. Hydrothermal liquefaction (HTL) is an attractive technology capable of converting a broad range of organic compounds, especially those with substantial water content, into energy products. The HTL process produces a bio-oil precursor that can be further upgraded to transportation fuels and an aqueous phase containing water-soluble organic impurities. Converting small oxygenated compounds that partition into the water phase into larger, hydrophobic compounds can reduce aqueous phase remediation costs and improve energy yields. HTL was investigated at 300 °C and a reaction time of 1 h for conversion of an institutional food waste to bio-oil, using either homogeneous Na2CO3 or heterogeneous CeZrOx to promote in situ conversion of water-soluble organic compounds into less oxygenated, oil-soluble products. Results with food waste indicate that CeZrOx improves both bio-oil higher heating value (HHV) and energy recovery when compared both to non-catalytic and Na2CO3-catalyzed HTL. The aqueous phase obtained using CeZrOx as an HTL catalyst contained approximately half the total organic carbon compared to that obtained using Na2CO3—suggesting reduced water treatment costs using the heterogeneous catalyst. Experiments with model compounds indicated that the primary mechanism of action was condensation of aldehydes, a reaction which simultaneously increases molecular weight and oxygen-to-carbon ratio—consistent with the improvements in bio-oil yield and HHV observed with institutional food waste. The catalyst was stable under hydrothermal conditions (≥16 h at 300 °C) and could be reused at least three times for conversion of model aldehydes to water insoluble products. Energy and economic analysis suggested favorable performance for the heterogeneous catalyst compared either to non-catalytic HTL or Na2CO3-catalyzed HTL, especially once catalyst lifetime differences were considered. The results of this study establish the potential of heterogeneous catalysts to improve HTL economics and energetics.

Catalytic Hydrothermal Liquefaction of Food Waste Using CeZrOx

Prediction of the Knock Limit and Viable Operating Range for a Homogeneous-Charge Compression-Ignition (HCCI) Engine

A proton transfer reaction mass spectrometer was used to measure the concentrations of selected volatile organic compounds in the exhaust of a commercial turbofan aircraft engine. Nine different compounds including methanol, acetaldehyde, acetic acid, benzene, toluene, phenol, styrene, naphthalene, and the methylnaphthalenes were identified as engine exhaust components that are free of spectral interferences and quantifiable by the proton transfer reaction mass spectrometer. The emission characteristics of the engine were examined as a function of engine power, fuel composition, and downstream distance from the engine. The hydrocarbon emission indices were found to be highly variable, upwards to a factor of 10 for the same nominal engine power setting. Although the magnitude of the HC emissions exhibited large variation, we observed that plots of the HC emission indices versus that of the emission index determined for formaldehyde (normalized plots) were linear and essentially independent of power setting and fuel composition, which suggests that the HC emissions scale together. The results of this study are critically examined and are shown to compare favorably with those of previous studies and serve to validate the proton transfer reaction mass spectrometer method as a reliable quantitative technique for online monitoring of selected hydrocarbon emissions within the engine exhaust matrix.

Paul E. Yelvington

Papers

Global sensitivity analysis for systems with independent and/or correlated inputs.

Chemical Speciation of Hydrocarbon Emissions from a Commercial Aircraft Engine

Catalytic Hydrothermal Liquefaction of Food Waste Using CeZrOx

Prediction of the Knock Limit and Viable Operating Range for a Homogeneous-Charge Compression-Ignition (HCCI) Engine

Quantification of Aircraft Engine Hydrocarbon Emissions Using Proton Transfer Reaction Mass Spectrometry