Preheating

The authors present experimental studies of the deflagration-to-detonation transition (DDT) in tubes with smooth and rough walls in stoichiometric hydrogen-oxygen and ethylene-oxygen mixtures. On the basis of experimental evidence, it is shown that formation of the preheat zone, where reaction is chemically frozen, promotes the transition to detonation if temperature and width of the preheat zone are above certain critical values. A sequence of high-speed Schlieren records permits an accurate determination of the minimal values of temperature and width of the preheat zone, leading to transition to detonation. The experimentally measured critical temperatures and widths of the preheat zone initiating restructuring of the flame and transition to detonation in hydrogen-oxygen and ethylene-oxygen mixtures are consistent with the developed theory.

The aim of this work is to study the effect of properties of Karanja (Pongamia pinnata) methyl ester on
combustion, and NOx (oxides of nitrogen) emissions of a diesel engine. The properties of the karanja
methyl ester such as viscosity, density, bulk modulus, calorific value, iodine value, cetane number,
saturation% and oxygen% are considered for this study. Experiments were conducted in a naturally
aspirated, single cylinder, four-stroke, stationary, water cooled, constant rpm, in-line (fuel pumppressure
tube-fuel injector) direct injection diesel engine. The engine tests were conducted with karanja
methyl ester (with and without preheating), and baseline fossil diesel. The peak pressures and peak
heat release rates for methyl ester was slightly higher than diesel fuel. The crank angles for peak
pressure of the karanja methyl ester are very close to top dead center. This is probably due to dynamic
injection advance caused by their higher bulk modulus. However, the peak cylinder pressures for
preheated methyl ester decreases, due to late injection and faster evaporation of the fuel. It was
observed that, at full load the oxides of nitrogen emissions of karanja methyl ester are increased by 6%.
A significant reduction in oxides of nitrogen emission is observed with preheated methyl ester

The purpose of this study is to examine the influence of key properties of pongamia biodiesel on engine performance, combustion, and emission characteristics of direct injection diesel engine. The key properties of the pongamia biodiesel such as viscosity, density, bulk modulus, calorific value, iodine value, cetane number, saturation% and oxygen% are considered for this study. Experiments were conducted in a naturally aspirated, single cylinder, four-stroke, stationary, water cooled, constant rpm, in-line (pump-high pressure tube-fuel injector) direct injection diesel engine with pongamia biodiesel (with and without preheating), and petroleum diesel as fuels. The performance was evaluated in terms of fuel consumption, brake specific energy consumption, and thermal efficiency. A significant improvement in thermal efficiency was observed with preheated biodiesel. The peak pressures and peak heat release rates for biodiesel was slightly higher than diesel fuel. The high peak pressures of the biodiesel are probably due to dynamic injection advance caused by its higher bulk modulus. The higher values of peak heat release rates indicate better premixed combustion with the biodiesel. However, the peak pressures for preheated biodiesel decreases due to late injection and faster evaporation of the fuel. It was observed that at full load the nitric oxide emission of biodiesel is increased by 6 %. The hydrocarbon emissions of the biodiesel are very low and are reduced up to 32 % as compared to that of diesel fuel. There is a significant reduction in all exhaust gaseous emissions. Also a considerable reduction in nitric oxide emission is observed with preheated biodiesel due to change in premixed combustion phase. However when the preheated biodiesel is used, the smoke emission was increased due to prolonged combustion (diffusion) at lower viscosity. A considerable reduction in carbon monoxide emission as also observed with the preheated biodiesel.

The major drawback of vegetable oil fuels is their high viscosity. Various conventional approaches to reducing the viscosity of vegetable oils are studied theoretically and experimentally. An attempt to reduce the viscosity of the palm oil methyl esters (POME) by preheating the fuel was performed and a comparison on the basis of its projected chance of leading to 'diesel-like' combustion was also carried out with conventional diesel fuel. It was observed that by preheating the POME fuel above the conventional temperature, the engine performance, especially the brake power output and the exhaust emissions characteristics, is improved significantly, approaching 'diesel-like' performance. This is mainly attributed to the fact that as the fuel is preheated the viscosity is reduced close to ordinary diesel (OD) fuel. This will result in improved spray and atomization characteristics. Torque, brake power, specific fuel consumption, exhaust emissions and brake thermal efficiencies were measured and calculated. The potential for improved engine performance and reduction in emissions levels was demonstrated. © IMechE 1996.

http://pia.sagepub.com/content/210/2/131.short

Drawbacks associated with crude vegetable oils (high viscosity and low volatility) and alcohol (low energy content and cetane number) for use in compression ignition engine call for biodiesels. These biodiesels have numerous advantages compared to fossil fuels as they are renewable, biodegradable, provide energy security and foreign exchange savings besides addressing environmental concerns and socio-economic issues. However, these alternative fuels (vegetable oils and its biodiesels) are highly to moderate viscous and require hot combustion chamber, provided by semi adiabatic diesel engine. Investigations were carried out to determine exhaust emissions of a high grade semi adiabatic diesel engine consisted of air gap insulated piston, air gap insulated liner and ceramic coated cylinder head with dif erent operating conditions [normal temperature and pre-heated temperature] of crude rice bran oil and its biodiesel with varied injector opening pressure. Exhaust emissions were determined at various values of brake mean effective pressure of the engine fuelled with crude rice bran oil and its biodiesel. Comparative studies on exhaust emissions were made with diesel working on similar conditions. Particulate emissions decreased, while NOx levels increased with LHR engine with biodiesel operation. Exhaust emissions improved with increase of injector opening pressure and preheating of biodiesel.

PURPOSE:

Heat of composite polymerization (HP) indicates setting efficacy and temperature increase of composite in clinical procedures. The purpose of this in vitro experimental study was to evaluate the effects of 5 temperatures on HP of two new composites.
MATERIALS AND METHODS:

From each material (Core Max II [CM] and King Dental [KD]), 5 groups of 5 specimens each were prepared and their total HPs (J/gr) were measured and recorded, at one of the constant temperatures 0℃, 15℃, 23℃, 37℃ and 60℃ (2 × 5 × 5 specimens) using a differential scanning calorimetry (DSC) analyzer. The data were analyzed using a two-way ANOVA, a Tukey's test, an independent-samples t-test, and a linear regression analysis (α=0.05).
RESULTS:

No polymerization reactions occurred at 0℃; then this temperature was excluded from statistical analyses. The mean HP of the remaining 20 KD specimens was 20.5 ± 14.9 J/gr, while it was 40.7 ± 12.9 J/gr for CM. The independent-samples t-test showed that there were significant differences between the HP of the two materials at the temperatures 15℃ (P=.0001), 23℃ (P=.0163), 37℃ (P=.0039), and 60℃ (P=.0106). Linear regression analysis showed statistically significant correlations between environment temperatures and HP of CM (R(2)=0.777).
CONCLUSION:

Using CM is advantageous over conventional composite because of its better polymerization capacity. However due to its high HP, further studies should assess its temperature increase in vivo. Preheating KD is recommended. Refrigerating composites can negatively affect their polymerization potential.

The aim of the study was to compare the marginal adaptation of three different resin-based materials used for direct restoration: hybrid composite resin (Gaenial Posterio, GC Corporation), a compomer (Dyract eXtra, Dentsply Sirona), and a giomer (Beautifil II, Shofu Dental) applied at room temperature or after preheated at preheating 50 and 60 o C. Class II cavities were prepared on proximal surfaces of extracted teeth and randomly divided in 3 groups according to the material used for restoration. In each group five cavities were restored using the materials at room temperature (subgroup 1), five cavities were restored using preheated materials at 50ºC (subgroup 2), and five cavities were restored using preheated materials at 60ºC (subgroup 3). The teeth were stored in distilled water for 14 days and then were immersed in 2% methylene blue buffered dye solution (pH = 7) for 4 hours. The teeth were transversally cut and the sections were examined using optical microscope (Carl-Zeiss AXIO Imager A1m) at 50x magnification and the dye penetration was evaluated according to 4 scores. Decreased microleakage and fewer gap formation were recorded for all filling materials after they have been heated at 50 or 60 o C. Pre-warming of resin-based materials improves the adaptation of these materials to tooth structures.

This paper presents the investigation of tool life improvement in end-milling of Titanium Alloy Ti-6Al-4V through workpiece preheating. End milling tests were conducted on Vertical Machining Centre with full immersion cutting. Induction heating was utilized during end milling for preheating. The titanium alloy Ti-6Al-4V bar was used as the workpiece. Machining was performed with a 20 mm diameter end-mill tool holder fitted with one PCD inserts. All of the experiments were run under room temperature and preheating condition at 315, 450, and 650ºC. Flank wear has been considered as the criterion for tool failure and the wear was measured using a Hisomet II Toolmaker's microscope. Tests were conducted until an insert was rejected when an average flank wear greater than 0.30 mm was recorded. Cutting force and torque measurements were conducted using the Kistler Rotating Cutting Force Dynamometer. Vibration during cutting was captured using an online vibration monitoring system. Sca...

The origin of the hot phase of the early universe remains so far an unsolved puzzle. A viable option is entropy production through the decays of heavy Majorana neutrinos whose lifetimes determine the initial temperature. We show that baryogenesis and the production of dark matter are natural by-products of this mechanism. As is well known, the cosmological baryon asymmetry can be accounted for by leptogenesis for characteristic neutrino mass parameters. We find that thermal gravitino production then automatically yields the observed amount of dark matter, for the gravitino as the lightest superparticle and typical gluino masses. As an example, we consider the production of heavy Majorana neutrinos in the course of tachyonic preheating associated with spontaneous B−L breaking. A quantitative analysis leads to constraints on the superparticle masses in terms of neutrino masses: For a light neutrino mass of 10^−5 eV the gravitino mass can be as small as 200 MeV, whereas a lower neutrino mass bound of 0.01 eV implies a lower bound of 9 GeV on the gravitino mass. The measurement of a light neutrino mass of 0.1 eV would rule out heavy neutrino decays as the origin of entropy, visible and dark matter.

We study tachyonic preheating associated with the spontaneous breaking of B−L, the difference of baryon and lepton number. Reheating occurs through the decays of heavy Majorana neutrinos which are produced during preheating and in decays of the Higgs particles of B−L breaking. Baryogenesis is an interplay of nonthermal and thermal leptogenesis, accompanied by thermally produced gravitino dark matter. The proposed mechanism simultaneously explains the generation of matter and dark matter, thereby relating the absolute neutrino mass scale to the gravitino mass.