An Analysis of the Combustion Behavior of Ethanol, Butanol, Iso-Octane, Gasoline, and Methane in a Direct-Injection Spark-Ignition Research Engine

Future automotive fuels are expected to contain significant quantities of bio-components. This poses a great challenge to the designers of novel low-CO2 internal combustion engines because biofuels have very different properties to those of most typical hydrocarbons. The current article presents results of firing a direct-injection spark-ignition optical research engine on ethanol and butanol and comparing those to data obtained with gasoline and iso-octane. A multihole injector, located centrally in the combustion chamber, was used with all fuels. Methane was also employed by injecting it into the inlet plenum to provide a benchmark case for well-mixed “homogeneous” charge preparation. The study covered stoichiometric and lean mixtures (λ = 1.0 and λ = 1.2), various spark advances (30–50° CA), a range of engine temperatures (20–90°C), and diverse injection strategies (single and “split” triple). In-cylinder gas sampling at the spark-plug location and at a location on the pent-roof wall was also carried out using a fast flame ionization detector to measure the equivalence ratio of the in-cylinder charge and identify the degree of stratification. Combustion imaging was performed through a full-bore optical piston to study the effect of injection strategy on late burning associated with fuel spray wall impingement. Combustion with single injection was fastest for ethanol throughout 20–90°C, but butanol and methane were just as fast at 90°C; iso-octane was the slowest and gasoline was between iso-octane and the alcohols. At 20°C, λ at the spark plug location was 0.96–1.09, with gasoline exhibiting the largest and iso-octane the lowest value. Ethanol showed the lowest degree of stratification and butanol the largest. At 90°C, stratification was lower for most fuels, with butanol showing the largest effect. The work output with triple injection was marginally higher for the alcohols and lower for iso-octane and gasoline (than with single injection), but combustion stability was worse for all fuels. Triple injection produced a lower degree of stratification, with leaner λ at the spark plug than single injection. Combustion imaging showed much less luminous late burning with tripe injection. In terms of combustion stability, the alcohols were more robust to changes in fueling (λ = 1.2) than the liquid hydrocarbons

Thermal Emission and Albedo Spectra of Super Earths with Flat Transmission Spectra

Planets larger than Earth and smaller than Neptune are some of the most numerous in the galaxy, but observational efforts to understand this population have proved challenging because optically thick clouds or hazes at high altitudes obscure molecular features (Kreidberg et al. 2014b). We present models of super Earths that include thick clouds and hazes and predict their transmission, thermal emission, and reflected light spectra. Very thick, lofted clouds of salts or sulfides in high metallicity (1000x solar) atmospheres create featureless transmission spectra in the near-infrared. Photochemical hazes with a range of particle sizes also create featureless transmission spectra at lower metallicities. Cloudy thermal emission spectra have muted features more like blackbodies, and hazy thermal emission spectra have emission features caused by an inversion layer at altitudes where the haze forms. Close analysis of reflected light from warm (~400-800 K) planets can distinguish cloudy spectra, which have moderate albedos (0.05-0.20), from hazy models, which are very dark (0.0-0.03). Reflected light spectra of cold planets (~200 K) accessible to a space-based visible light coronagraph will have high albedos and large molecular features that will allow them to be more easily characterized than the warmer transiting planets. We suggest a number of complementary observations to characterize this population of planets, including transmission spectra of hot (>1000 K) targets, thermal emission spectra of warm targets using the James Webb Space Telescope (JWST), high spectral resolution (R~10^5) observations of cloudy targets, and reflected light spectral observations of directly-imaged cold targets. Despite the dearth of features observed in super Earth transmission spectra to date, different observations will provide rich diagnostics of their atmospheres.Comment: 23 pages, 23 figures. Revised for publication in The Astrophysical Journa

Synchrotron x-ray imaging visualization study of capillary-induced flow and critical heat flux on surfaces with engineered micropillars

Over the last several decades, phenomena related to critical heat flux (CHF) on structured surfaces have received a large amount of attention from the research community. The purpose of such research has been to enhance the safety and efficiency of a variety of thermal systems. A number of theories have been put forward to explain the key CHF enhancement mechanisms on structured surfaces. However, these theories have not been confirmed experimentally because of limitations in the available visualization techniques and the complexity of the phenomena. To overcome these limitations and elucidate the CHF enhancement mechanism on the structured surfaces, we introduce synchrotron x-ray imaging with high spatial (similar to 2 mu m) and temporal (similar to 20,000 Hz) resolutions. This technique has enabled us to confirm that capillary-induced flow is the key CHF enhancement mechanism on structured surfaces.11Ysciescopu

Single-Stage, Venturi-Driven Desalination System

Water demand is increasing at a rapid pace due to population increase, industrial expansion, and agricultural development. The use of desalination technology to meet the high water demands has increased global online desalination capacity from 47 million m^3/d in 2007 to 92.5 million m^3/d as of June 2017 [49]. Membrane and thermal processes are the two mainstream desalination categories used worldwide for desalination plants. Reverse Osmosis (RO) is the most widely used membrane process and it has become the dominant technology for building desalination plants over recent decades. Thermal distillation, however, has become less and less competitive due to its high production costs, mainly due to a reliance on increasing fuel prices and large thermal energy requirements. Although heat recuperation is commonly used, it adds investment cost and increases complexity of the system. The concept of Single-Stage Venturi-driven (SSV) Desalination, a single-stage, thermal desalination system, using a Multifunctional Venturi Water Ejector (Venturi system), is proposed, analyzed, and demonstrated. The system requires only low-grade solar heat (\u3c 60 °C) mainly to supplement the heat loss during operation. As compared to the conventional methods of solar desalination, the proposed system has the following intellectual novelties: First, the novel multifunctional water ejector integrates a vacuum pump for steam production, a compressor for condensation, and a starter for heat recuperation. Second, only residential-grade solar water heating is needed for the heat demand which greatly reduces the production cost of solar desalination, as compared to those systems using concentrated solar power (CSP). Third, the proposed system is operated standalone based solely on solar energy. The main objective of this research is to accurately analyze and model the SSV system, and achieve an estimated levelized cost of water (LCOW) close to the DOE target of $0.50/m3 (DE-FOA-0001778) [55]. Additionally, prototypes, operating at about 0.1 bar, were built to prove the concept that very low-grade heat sources can be utilized with the system. While similar to other thermal methods, such as MSF (multi-stage flash desalination), MED (multi-effect desalination), and VC (vapor compression desalination), the SSV system utilizes a unique water ejector to reduce vapor pressure in a “boiler” and operate at lower temperatures, thereby increasing the heat regeneration efficiency and decreasing the heat input temperature requirements. The concept, as well as the scalability, of the system is proven in the results. The performance of the Venturi System was simulated using Comsol Multiphysics. The simulation results were compared to both the theoretical and experimental results. The lowest experimental vacuum pressure achieved during operation was 0.07 bar, equating to a boiling point of 40 ℃. High-performance, customized Venturi water ejector designs are projected to further lower vacuum pressures. In this study, a thermo-economic analysis was performed as a theoretical baseline for the performance of the novel technology. In the future, the baseline results should be compared to experimental results of a pilot or operational SSV desalination plant. The resulting energy requirements of the system are calculated as 40.6 kWh/m3 for thermal and 0.23 kWh/m3 for electrical energy requirements. The performance ratio and exergy efficiency are calculated as 15.4 and 39$0.67/m3, achieving a lower price point than most commercialized solar desalination technologies