A comparative analysis of knock severity in a Cooperative Fuel Research engine using binary gasoline–alcohol blends

Knock remains one of the main limitations for increasing the efficiency in spark-ignition engines. The use of certain alcohol–gasoline blends is an effective way to either mitigate or eliminate knock, allowing the use of higher compression ratios, therefore increasing the efficiency of spark-ignition engines. Methanol and ethanol are alcohols commonly employed for reducing knock, due to their higher octane number and vaporization heat value. Major attention is being paid recently to butanol and its blends with gasoline since they present similar characteristics to gasoline; however, it was found to be the least knock resistant among the three fuels. In the present work, a comparison between the knock performance of methanol–gasoline, ethanol–gasoline and butanol–gasoline blends is carried out, by volume concentrations up to 20 v/v%. This comparison is made in terms of knock intensity and knock probability. Tests are performed in a single-cylinder, variable-compression ratio, Cooperative Fuel Research engine equipped with port fuel injection system, facilitating the comparison against future results obtained by similar experimental facilities. Results obtained allow to reach meaningful conclusions about the capacity of each blend to mitigate knock.

Vaporization Heat Transfer in a Small Diameter Closed Two-Phase Thermosyphon

This paper deals with vaporization heat transfer in a small diameter closed two-phase thermosyphon with a long evaporator and a short condenser, filled with water as operating fluid. The internal diameter of the evaporator is equal to 6.4 mm and the length-to-diameter ratio at the evaporator is equal to 166. A similar geometry is commonly used in vacuumed tube solar collectors. In the present investigation, the input power to the evaporator is provided by means of an electrical resistance wire wrapped around the external wall of the tube, while a water jacket is built at the condenser to reject the heat. The performance of the thermosyphon is described by using the wall temperature and the overall thermal resistance for different operating conditions: input power at the evaporator, cooling water temperature at the condenser, and inclination of the thermosyphon (30 deg, 60 deg, and 90 deg tilt angle to the horizontal plane). The present experimental data cover a range of heat flux between 1700 and 8000 W/m2 and saturation temperature between 28 °C and 72 °C. The vaporization heat transfer coefficients are compared with some correlations for closed two-phase thermosyphons displaying large disagreement. A new correlation is presented, which accurately predicts the present experimental values and other data by independent labs taken in closed two-phase thermosyphons, varying geometry and operating fluid (water, R134a, and ethanol).

Vaporization heat of bound water in wood chemically modified via grafting and crosslinking patterns by DSC and NMR analysis

Radiata pine wood (W) was modified with acetic anhydride and glutaraldehyde (GA) resulting in WAcand WGAto various weight percent gains (WPGs), whereas in WActhe effect is due to grafting and in WGA, crosslinking. The heat of vaporization of bound water (BW) of the modified woods was studied by differential scanning calorimetry (DSC) and the mass loss (due to water loss) of the samples by thermogravimetry (TG). The temperature program was in both cases from 25 to 40°C with 10°C min−1. The adsorbed or condensed water in wood were observed via low-field nuclear magnetic resonance (LFNMR). At a comparable WPG level, the LFNMR analysis showed that the interaction of water with WGAwas stronger than that with WAc. In both modified woods, a considerable reduction in the vaporization heat of BW was visible due to cell wall hydrophobization and bulking. The reduction of condensed water in micropores was lower for WGAthan WAc, probably because BW needs more energy to evaporate from the crosslinked stiff WGAcell walls.

Effect of Humidity on Condensation in Vapour Compression Refrigeration System for Fresh Foods Transport Vehicles

In today’s world the developed countries rely on the refrigerated container (reefer) vehicles for the transportation of cold chain products such as fresh foods. In India this technology was introduced in late 1980s but the growth was very slow compared to other countries and failed to match the international trends. However recently, with fast development of roadways, urbanisation and connectivity the reefers get a massive response. The reefers have several advantages but they consume considerable amount of electrical energy to operate. Reefer works based on vapour compression refrigeration cycle in which condenser is an important device. This condenser uses fan-blown atmospheric air over it to remove vaporization heat from refrigerant. The temperature of refrigerant after condensation has effects on Coefficient of performance (COP) of the refrigeration system. This temperature can be altered by the relative humidity of air. The result of our project shows that the increase in air humidity by 18.60% increases the COP by 11.37% and also it reduces the power consumption.

Quantum Dot Temperature Sensor Ab Initio Test: Droplet Vaporization Heat Transfer

Better understanding of phase change phenomena can be obtained through local measurements of the heat transfer process, which can’t be attained by traditional thermocouple point measurements. Infrared (IR) technology, which has been used by many researchers in the past, cannot be used under certain circumstances due to spectral transparency issues present in some materials. In the current study, Quantum Dots (QDs) are proposed as a novel tool for heat transfer measurements. QDs are nano-sized semiconductor materials which fluoresce upon excitation by blue or UV light. The light intensity emitted by QDs drops with temperature, which can be utilized to obtain the surface temperature distribution at a camera pixel resolution. If QDs are distributed on a surface of interest and optical access to that surface is available, the heat transfer processes can be examined using inexpensive equipment such as CCD/CMOS cameras and LED excitation sources. In this paper, a description of a QD based technique is given, where it is applied to visualize the heat transfer associated with ethanol droplet evaporation.

Water liquid-vapor equilibrium by molecular dynamics: Alternative equilibrium pressure estimation

The molecular dynamics simulations of the liquid-vapor equilibrium of water including both water phases — liquid and vapor — in one simulation are presented. Such approach is preferred if equilibrium curve data are to be collected instead of the two distinct simulations for each phase separately. Then the liquid phase is not restricted, e.g. by insufficient volume resulting in too high pressures, and can spread into its natural volume ruled by chosen force field and by the contact with vapor phase as vaporized molecules are colliding with phase interface. Averaged strongly fluctuating virial pressure values gave untrustworthy or even unreal results, so need for an alternative method arisen. The idea was inspired with the presence of vapor phase and by previous experiences in gaseous phase simulations with small fluctuations of pressure, almost matching the ideal gas value. In presented simulations, the first idea how to calculate pressure only from the vapor phase part of simulation box were applied. This resulted into very simple method based only on averaging molecules count in the vapor phase subspace of known volume. Such simple approach provided more reliable pressure estimation than statistical output of the simulation program. Contrary, also drawbacks are present in longer initial thermostatization time or more laborious estimation of the vaporization heat. What more, such heat of vaporization suffers with border effect inaccuracy slowly decreasing with the thickness of liquid phase. For more efficient and more accurate vaporization heat estimation the two distinct simulations for each phase separately should be preferred.