Effects of Additives on the Non-Premixed Ignition of Ethylene in Air

The ignition characteristics of heated C_2H_4 counterflowing against heated air were numerically investigated in the presence of additives such as NO, F_2, and H_2. C_2H_4 and air temperatures were chosen to resemble conditions relevant to high-Mach number, air-breathing propulsion. The numerical simulations were conducted along the stagnation streamline of the counterflow and included detailed descriptions of chemical kinetics and molecular transport. It was found that addition of NO at concentrations of about 10,000 ppm (1%), results in a substantial increase of the ignition strain rate, from 300 /s to values up to 32,000/s. This ignition promotion is caused by enhanced radical production that is initiated through the interaction between NO and HO_2. A further increase in the NO amount leads to reduced improvements. Small additions of F_2 and H_2 were also found to promote ignition, but to lesser extent compared to NO. Results also show that with the addition of F_2 in the presence of NO, ignition promotion is further enhanced, and for F_2 and NO concentrations larger than 25,000 ppm, the system becomes hypergolic. The present investigations suggest that the use of C_2H_4, NO, and F_2 may permit ignition at conditions of relevance to SCRAMJET’s

A Comparative Numerical Study of Premixed and Non-Premixed Ethylene Flames

Detailed numerical simulations of premixed and non-premixed C_2H_4/air flames were conducted, using six available kinetic mechanisms. The results help assess differences between these mechanisms and are of interest to proposed hydrocarbon-fueled SCRAMJET concepts, in which C_2H_4 can be expected to be a major component of the thermally cracked fuel. For premixed flames, laminar flame speeds were calculated and compared with available experimental data. For non-premixed flames, ignition/extinction Z-curves were calculated for conditions of relevance to proposed SCRAMJET concepts. Results revealed a large variance in predictions of the kinetic mechanisms examined. Differences in laminar flame speeds as high as factors of 2.5 were found. For the conditions investigated, computed ignition and extinction strain rates for non-premixed flames differed by factors as high as 300 and 3, respectively. This indicates that while there are differences in high-temperature kinetics that control flame propagation and extinction, discrepancies in low-temperature kinetics that control ignition can be even more significant. Sensitivity- and species-consumption analyses indicate uncertainties in fuel kinetics and, most importantly, on the oxidation of C_2H_3 and the production of CH_2CHO, whose kinetics are not well known and can crucially affect production of the important H radicals. These findings stress the need for experimental data in premixed and non-premixed configurations that can be used to assess these phenomena and provide the basis for a comprehensive validation

Effects of Additives on the Non-Premixed Ignition of Ethylene in Air

The ignition characteristics of heated C_2H_4 counterflowing against heated air were numerically investigated in the presence of additives such as NO, F_2, and H_2. C_2H_4 and air temperatures were chosen to resemble conditions relevant to high-Mach number, air-breathing propulsion. The numerical simulations were conducted along the stagnation streamline of the counterflow and included detailed descriptions of chemical kinetics and molecular transport. It was found that addition of NO at concentrations of about 10,000 ppm (1%), results in a substantial increase of the ignition strain rate, from 300 /s to values up to 32,000/s. This ignition promotion is caused by enhanced radical production that is initiated through the interaction between NO and HO_2. A further increase in the NO amount leads to reduced improvements. Small additions of F_2 and H_2 were also found to promote ignition, but to lesser extent compared to NO. Results also show that with the addition of F_2 in the presence of NO, ignition promotion is further enhanced, and for F_2 and NO concentrations larger than 25,000 ppm, the system becomes hypergolic. The present investigations suggest that the use of C_2H_4, NO, and F_2 may permit ignition at conditions of relevance to SCRAMJET’s

A Comparative Numerical Study of Premixed and Non-Premixed Ethylene Flames

Detailed numerical simulations of premixed and non-premixed C_2H_4/air flames were conducted, using six available kinetic mechanisms. The results help assess differences between these mechanisms and are of interest to proposed hydrocarbon-fueled SCRAMJET concepts, in which C_2H_4 can be expected to be a major component of the thermally cracked fuel. For premixed flames, laminar flame speeds were calculated and compared with available experimental data. For non-premixed flames, ignition/extinction Z-curves were calculated for conditions of relevance to proposed SCRAMJET concepts. Results revealed a large variance in predictions of the kinetic mechanisms examined. Differences in laminar flame speeds as high as factors of 2.5 were found. For the conditions investigated, computed ignition and extinction strain rates for non-premixed flames differed by factors as high as 300 and 3, respectively. This indicates that while there are differences in high-temperature kinetics that control flame propagation and extinction, discrepancies in low-temperature kinetics that control ignition can be even more significant. Sensitivity- and species-consumption analyses indicate uncertainties in fuel kinetics and, most importantly, on the oxidation of C_2H_3 and the production of CH_2CHO, whose kinetics are not well known and can crucially affect production of the important H radicals. These findings stress the need for experimental data in premixed and non-premixed configurations that can be used to assess these phenomena and provide the basis for a comprehensive validation

Measuring affective well-being at work using short-form scales : implications for affective structures and participant instructions

Measuring affective well-being in organizational studies has become increasingly widespread, given its association with key work-performance and other markers of organizational functioning. As such, researchers and policy-makers need to be confident that well-being measures are valid, reliable and robust. To reduce the burden on participants in applied settings, short-form measures of affective well-being are proving popular. However, these scales are seldom validated as standalone, comprehensive measures in their own right. In this article, we used a short-form measure of affective well-being with 10 items: the Daniels five-factor measure of affective well-being (D-FAW). In Study 1, across six applied sample groups (N = 2624), we found that the factor structure of the short-form D-FAW is robust when issued as a standalone measure, and that it should be scored differently depending on the participant instruction used. When participant instructions focus on now or today, then affect is best represented by five discrete emotion factors. When participant instructions focus on the past week, then affect is best represented by two or three mood-based factors. In Study 2 (N = 39), we found good construct convergent validity of short-form D-FAW with another widely used scale (PANAS). Implications for the measurement and structure of affect are discussed

Understanding bottom-up continuous hydrothermal synthesis of nanoparticles using empirical measurement and computational simulation

Continuous hydrothermal synthesis was highlighted in a recent review as an enabling technology for the production of nanoparticles. In recent years, it has been shown to be a suitable reaction medium for the synthesis of a wide range of nanomaterials. Many single and complex nanomaterials such as metals, metal oxides, doped oxides, carbonates, sulfides, hydroxides, phosphates, and metal organic frameworks can be formed using continuous hydrothermal synthesis techniques. This work presents a methodology to characterize continuous hydrothermal flow systems both experimentally and numerically, and to determine the scalability of a counter current supercritical water reactor for the large scale production (>1,000 T·year–1) of nanomaterials. Experiments were performed using a purpose-built continuous flow rig, featuring an injection loop on a metal salt feed line, which allowed the injection of a chromophoric tracer. At the system outlet, the tracer was detected using UV/Vis absorption, which could be used to measure the residence time distribution within the reactor volume. Computational fluid dynamics (CFD) calculations were also conducted using a modeled geometry to represent the experimental apparatus. The performance of the CFD model was tested against experimental data, verifying that the CFD model accurately predicted the nucleation and growth of the nanomaterials inside the reactor