Global patient outcomes after elective surgery: prospective cohort study in 27 low-, middle- and high-income countries.

BACKGROUND: As global initiatives increase patient access to surgical treatments, there remains a need to understand the adverse effects of surgery and define appropriate levels of perioperative care. METHODS: We designed a prospective international 7-day cohort study of outcomes following elective adult inpatient surgery in 27 countries. The primary outcome was in-hospital complications. Secondary outcomes were death following a complication (failure to rescue) and death in hospital. Process measures were admission to critical care immediately after surgery or to treat a complication and duration of hospital stay. A single definition of critical care was used for all countries. RESULTS: A total of 474 hospitals in 19 high-, 7 middle- and 1 low-income country were included in the primary analysis. Data included 44 814 patients with a median hospital stay of 4 (range 2-7) days. A total of 7508 patients (16.8%) developed one or more postoperative complication and 207 died (0.5%). The overall mortality among patients who developed complications was 2.8%. Mortality following complications ranged from 2.4% for pulmonary embolism to 43.9% for cardiac arrest. A total of 4360 (9.7%) patients were admitted to a critical care unit as routine immediately after surgery, of whom 2198 (50.4%) developed a complication, with 105 (2.4%) deaths. A total of 1233 patients (16.4%) were admitted to a critical care unit to treat complications, with 119 (9.7%) deaths. Despite lower baseline risk, outcomes were similar in low- and middle-income compared with high-income countries. CONCLUSIONS: Poor patient outcomes are common after inpatient surgery. Global initiatives to increase access to surgical treatments should also address the need for safe perioperative care. STUDY REGISTRATION: ISRCTN5181700

Reduced kinetic mechanism for methanol combustion in spark-ignition engines

A reduced kinetic mechanism for methanol combustion at spark-ignition (SI) engine conditions is presented. The mechanism consists of 18 species and 55 irreversible reactions, small enough to be suitable for large eddy simulations (LES). The mechanism was reduced and optimized using the comprehensive mechanism (AramcoMech 2.0) as a starting point, to maintain performance at stoichiometric conditions for the pressure (10-50 bar) and temperature ranges relevant for SI-engine conditions. The mechanism was validated against experimental data for ignition delay at 1050-1650 K, flow reactor at 783 K and jet-stirred reactors at 800-1150 K, and simulated validation targets for laminar burning velocity under conditions where no experimental data are available. The mechanism performs well for pollutant formation (CO and CH2O), ignition delay, and laminar burning velocity, which are all important properties for LES of engines. Two other reduced mechanisms for methanol combustion, containing around the same number of species and reactions, were tested for comparison. The superior performance of the mechanism developed in the present work is likely a result of that it is specifically produced for the relevant conditions, while the other mechanisms were developed for a limited set of conditions compared to the present work. This highlights the importance of careful selection of reduced mechanisms for implementation in computational fluid dynamics simulations

Composition of Reduced Mechanisms for Ignition of Biodiesel Surrogates

Chemical kinetics mechanisms describing Fatty Acid Methyl Ester (FAME) biofuel combustion are quite extensive and cannot be implemented in Computational Fluid Dynamics simulations of real engine systems. Using the reduction methodology Ant Colony Reduction (ACR), skeletal reduction followed by optimization has been performed for the C-11 FAME biodiesel components methyl decanoate (MD), methyl 5-decenoate (MDe5), and methyl 9-decenoate (MDe9), and for the alkane n-decane. The aim of the present study was to produce small reduced mechanisms accurately describing ignition of the fuels over a wide range of conditions, and in addition to compare the size and composition of reduced mechanisms constructed from two parent mechanisms of different complexity. Reduction targets were ignition delay times over a wide range of equivalence ratios and pressures, for separate temperature ranges of 600–1100 K (LT) and 1100–1500 K (HT). One of the complex mechanisms was constructed to be simplified by a lumping approach and this one included MD and was also used to perform reduction for the alkane n-decane. The most detailed parent mechanism was used to create reduced mechanisms for all the three methyl esters. The lumped complex mechanisms resulted in more compact reduced mechanisms, 157 reactions for LT of MD, compared to 810 reactions for the more detailed mechanism. MD required the largest fuel breakdown subsets while the unsaturated methyl esters could be described by smaller subsets. All mechanisms had similar subsets for the smallest hydrocarbons and H/O chemistry, independent of the fuel and the choice of parent mechanism. The ACR approach for mechanism reduction created reduced mechanisms with high accuracy for all conditions included in the present study

Evaluation of Chemical Kinetic Mechanisms for Methane Combustion: A Review from a CFD Perspective

Methane is an important fuel for gas turbine and gas engine combustion, and the most common fuel in fundamental combustion studies. As Computational Fluid Dynamics (CFD) modeling of combustion becomes increasingly important, so do chemical kinetic mechanisms for methane combustion. Kinetic mechanisms of different complexity exist, and the aim of this study is to review commonly used detailed, reduced, and global mechanisms of importance for CFD of methane combustion. In this review, procedures of relevance to model development are outlined. Simulations of zero and one-dimensional configurations have been performed over a wide range of conditions, including addition of H2, CO2 and H2O, and the results are used in a final recommendation about the use of the different mechanisms. The aim of this review is to put focus on the importance of an informed choice of kinetic mechanism to obtain accurate results at a reasonable computational cost. It is shown that for flame simulations, a reduced mechanism with only 42 irreversible reactions gives excellent agreement with experimental data, using only 5% of the computational time as compared to the widely used GRI-Mech 3.0. The reduced mechanisms are highly suitable for flame simulations, while for ignition they tend to react too slow, giving longer than expected ignition delay time. For combustible mixtures with addition of hydrogen, carbon dioxide, or water, the detailed as well as reduced mechanisms generally show as good performance as for the corresponding simulations of pure methane/air mixtures

Reduced Chemical Kinetic Reaction Mechanism for Dimethyl Ether-Air Combustion

Development and validation of a new reduced dimethyl ether-air (DME) reaction mechanism is presented. The mechanism was developed using a modular approach that has previously been applied to several alkane and alkene fuels, and the present work pioneers the use of the modular methodology, with its underlying H/C1/O base mechanism, on an oxygenated fuel. The development methodology uses a well-characterized H/C1/O base mechanism coupled to a reduced set of fuel and intermediate product submechanisms. The mechanism for DME presented in this work includes 30 species and 69 irreversible reactions. When used in combustion simulation the mechanism accurately reproduced key combustion characteristics and the small size enables use in computationally demanding Large Eddy Simulations (LES) and Direct Numerical Simulations (DNS). It has been developed to accurately predict, among other parameters, laminar burning velocity and ignition delay times, including the negative temperature regime. The evaluation of the mechanism and comparison to experimental data and several detailed and reduced mechanisms covers a wide range of conditions with respect to temperature, pressure and fuel-to-air ratio. There is good agreement with experimental data and the detailed reference mechanisms at all investigated conditions. The mechanism uses fewer reactions than any previously presented DME-air mechanism, without losing in predictability

Evaluation of combustion properties of vent gases from Li-ion batteries

Fire incidents involving Li-ion batteries is an increasing concern as the use of battery electric vehicles is increasing. Abuse conditions such as heating can result in ejection of flammable and toxic gases, presenting a health risk and risk of explosion or fire. The purpose of the present work is to increase the understanding of combustion of gas mixtures vented from Li-ion batteries. The investigation uses a new merged kinetic mechanism including hydrocarbons, hydrogen, carbon oxides, carbonates and fluorinated compounds. Seven typical Li-ion vent gas mixtures were selected based on published studies, and ignition and laminar flames were simulated. Modeling reveal a large variation in laminar burning velocity, flame temperature and heat release. Determining factors for laminar flames are the relative content of the carbonates and hydrogen gas, and the inert carbon dioxide. Gases from highly charged battery cells have the shortest ignition time at high temperatures and the fastest laminar burning velocity. The results can be used as input in computational fluid dynamics or safety engineering modeling. In addition, the versatile kinetic model can be used for fundamental studies of the combustion process and for generation of combustion characteristics such as laminar burning velocities for other vent gas mixtures

Predictions of Spray Combustion using Conventional Category A Fuels and Exploratory Category C Fuels

Aviation currently contributes about 3% of the world’s CO2 emissions, 5% of the global warming, and 35% of the trade. Reducing the emissions and the global warming from aviation is thus essential. Many approaches to achieve this goal are underway, including H2, fuel cells, and batteries, but also by replacing the fossil jet fuel with sustainable jet fuel from non-fossil feedstocks. This involves many challenges, and among them we have the issue of current jet engines being developed for existing fossil jet fuels. To facilitate the change towards sustainable jet fuel, typically having different thermophysical and combustion properties compared to fossil jet fuels, we need to analyze the sensitivity of combustion to other fuels, having a wider range of thermophysical specifications. Here, we examine combustion of n-heptane, n-dodecane, Jet A, and two test fuels, C1 and C5 in three different combustors. The first and second cases are axisymmetric and rectilinear pre-vaporized premixed bluff-body stabilized flames, whereas the third is a single sector helicopter combustor for liquid fuel. A Finite Rate Chemistry (FRC) Large Eddy Simulation (LES) model is used together with small comprehensive reaction mechanisms of ~300 reactions. Comparison with experimental data is performed for the pre-vaporized combustor configurations. Good agreement is generally observed, and small to marginal differences in combustion behavior is observed between the different fuels

Kinetics of the reaction of Cl atoms with CHCl3 over the temperature range 253-313 K

The reaction CHCl3 + Cl → CCl3 + HCl was studied in the atmospherically relevant temperature range from 253 to 313 K and in 930 mbar of N2 diluent using the relative rate method. A temperature dependent reaction rate constant, valid in the temperature range 220-330 K, was determined by a fit to the result of the present study and that of Orlando (1999); k = (3.77 ± 0.32) × 10-12 exp((-1011 ± 24)/T) cm3 molecule-1 s-1

The comparative and combined effects of hydrogen addition on the laminar burning velocities of methane and its blends with ethane and propane

Laminar burning velocities of hydrocarbon blends of relevance to natural gas combustion, with addition of 0, 10, 35 and 50% hydrogen, were measured using the heat flux method. Hydrocarbon blends were methane (80%)/ethane (20%), methane (80%)/propane (20%) and methane (80%)/ethane (10%)/propane (10%), and in addition experiments were performed using pure methane as a fuel. For the first time it was shown experimentally that hydrogen promotes laminar burning velocity of blends with heavier hydrocarbons to a smaller extent than the well-studied effect on methane. Measurements show that enrichment by hydrogen results in 20–40% lower increase in laminar burning velocity for hydrocarbon blends compared to pure methane, depending on stoichiometry. Modeling points at the importance of increasing concentrations of OH, O and H radicals in H2 enriched flames. At lean conditions increase in H atom concentration is of particular importance. The results are rationalized based on asymptotic flame theory analysis

Gas-Phase Advanced Oxidation for Effective, Efficient in Situ Control of Pollution

In this article, gas-phase advanced oxidation, a new method for pollution control building on the photo-oxidation and particle formation chemistry occurring in the atmosphere, is introduced and characterized. The process uses ozone and UV-C light to produce in situ radicals to oxidize pollution, generating particles that are removed by a filter; ozone is removed using a MnO₂ honeycomb catalyst. This combination of in situ processes removes a wide range of pollutants with a comparatively low specific energy input. Two proof-of-concept devices were built to test and optimize the process. The laboratory prototype was built of standard ventilation duct and could treat up to 850 m³/h. A portable continuous-flow prototype built in an aluminum flight case was able to treat 46 m³/h. Removal efficiencies of >95% were observed for propane, cyclohexane, benzene, isoprene, aerosol particle mass, and ozone for concentrations in the range of 0.4–6 ppm and exposure times up to 0.5 min. The laboratory prototype generated a OH^• concentration derived from propane reaction of (2.5 ± 0.3) × 10¹⁰ cm^–3 at a specific energy input of 3 kJ/m³, and the portable device generated (4.6 ± 0.4) × 10⁹ cm^–3 at 10 kJ/m³. Based on these results, in situ gas-phase advanced oxidation is a viable control strategy for most volatile organic compounds, specifically those with a OH^• reaction rate higher than ca. 5 × 10^–13 cm³/s. Gas-phase advanced oxidation is able to remove compounds that react with OH and to control ozone and total particulate mass. Secondary pollution including formaldehyde and ultrafine particles might be generated, depending on the composition of the primary pollution