Study on Indium (III) Oxide/Aluminum Thermite Energetic Composites

Thermites or composite energetic materials are mixtures made of fuel and oxidizer particles at micron-scale. Thermite reactions are characterized by high adiabatic flame temperatures (>1000 °C) and high heats of reaction (>kJ/cm3), sometimes combined with gas generation. These properties strongly depend on the chemical nature of the couple of components implemented. The present work focuses on the use of indium (III) oxide nanoparticles as oxidizer in the elaboration of nanothermites. Mixed with an aluminum nanopowder, heat of reaction of the resulting Al/In2O3 energetic nanocomposite was calculated and its reactive performance (sensitivity thresholds regarding different stimuli (impact, friction, and electrostatic discharge) and combustion velocity examined. The Al/In2O3 nanothermite, whose heat of reaction was determined of about 11.75 kJ/cm3, was defined as insensitive and moderately sensitive to impact and friction stimuli and extreme sensitive to spark with values >100 N, 324 N, and 0.31 mJ, respectively. The spark sensitivity was decreased by increasing In2O3 oxidizer (27.71 mJ). The combustion speed in confined geometries experiments was established near 500 m/s. The nature of the oxidizer implemented herein within a thermite formulation is reported for the first time.

Effects of methane ratio on MPDF (micro-pilot dual-fuel) combustion characteristic in a heavy-duty single cylinder engine

In this study, the characteristics of micro-pilot dual-fuel combustion with respect to the fuel mixture ratio in a single cylinder dual-fuel engine have been investigated. In order to analyze the characteristics of micro-pilot dual-fuel combustion, a metal engine and an optical single cylinder dual-fuel engine were used. The fuel mixture ratio was varied for experimental purposes; the diesel was directly injected into combustion chamber and the methane gas was supplied via intake port. The present study reports that increasing the methane mixture ratio from 0 to 97.67% changes the diesel combustion to pre-mixed combustion. As a result, the peak cylinder pressure was increased from 184 to 198 bar, and the rate of heat release was greatly advanced. In the MPDF condition, the nitrogen oxides emissions were reduced by about 90%p, and the fuel conversion efficiency increased about 5%p because of the low combustion temperature of pre-mixed combustion. However, for the same reason, the hydrocarbon emissions were increased about 95%p. The fastest combustion speed was found form the results of methane mixture ratio between 40 and 80%. In the condition of diesel combustion and micro-pilot dual-fuel combustion, the combustion periods of middle and initial were increased, respectively, resulting in the low combustion speed. The standard deviation of peak cylinder pressure, which represents the combustion variation, was correlated with initial combustion period. While the condition of methane gas mixture ratio between 40 and 80% shows the lowest combustion variation, the highest combustion variation was occurred by MPDF condition. Through the optical engine experiment, it can be found that the cycle to cycle combustion variation is ascribed to the turbulent flow and the variation of ignition position. The combustion images show that the unpredictable characteristics of the ignition position and slow flame propagation speed caused the combustion variation in micro-pilot dual-fuel combustion.

COMBUSTION SPEED PARAMETERS WHEN SIMULATING BY ANSYS FLUENT PROGRAM OF SOLID FUEL COMBUSTION

The existing difference in the models used to describe the burning rate of solid fuel particles, and, accordingly, the difference in the constants appearing in them, determines the relevance of the formulation of the relation between the constants known from the literature and the parameters that must be set in programs for CFD modeling of heat and power processes. This, in particular, relates to modeling the combustion of solid fuels in the well-known program ANSYS FLUENT. The paper outlines a possible approach to solving this problem. Bibl. 5, Fig. 3.

The influence of the hydrogen injection timing on the IC engine working cycle

From an ecological aspect, the hydrogen has all properties to be a very good fuel for IC engines. However the high combustion speed, as well as the possibility of backfire, is inconvenient properties of port injection. In this paper, the influence of the injection timing on the IC engine working cycle parameters (pressure and temperature) was investigated deeply. The investigation, of the injection timing influence on the IC engine working cycle parameters, was performed numerically by application of ANSYS software. It was observed the geometry of the real engine with added pre chamber, in order of layer mixture formation and pressure damping, because of high combustion speed. The results are presented for four cases with different injection timing and the same spark timing. By earlier injection, the time for mixing rise as well as the possibility of homogenization and uniform mixture creation, in pre chamber and cylinder. This claim it is confirmed on the basis of obtaining pressure and pressure rise gradient, which are growing with earlier injection, because of hydrogen combustion characteristics in stoichiometric mixture. The higher pressures as well as the surface under the diagram are positive from the aspect of the engine efficiency. However, with the earlier injection, the values of the pressure rise gradient are higher than for the classic diesel engine. This means that this phenomena can cause brutal engine work from the aspect of mechanical stresses. However the value of the maximum pressure is smaller than this in a diesel engine, this is due to added pre chamber, which has decreased the compression ratio.

Numerical investigations on hydrogen-enhanced combustion in ultra-lean gasoline spark-ignition engines

Performance of lean-burn gasoline spark-ignition engines can be enhanced through hydrogen supplementation. Thanks to its physicochemical properties, hydrogen supports the flame propagation and extends the dilution limits with improved combustion stability. These interesting features usually result in decreased emissions and improved efficiencies. This article aims at demonstrating how hydrogen can support the combustion process with a modern combustion system optimized for high dilution resistance and efficiency. To achieve this, chemical kinetics calculations are first performed in order to quantify the impacts of hydrogen addition on the laminar flame speed and on the auto-ignition delay times of air/gasoline mixtures. These data are then implemented in the extended coherent flame model and tabulated kinetics of ignition combustion models in a specifically updated version of the CONVERGE code. Three-dimensional computational fluid dynamics engine calculations are performed at λ = 2 with 3% v/v of hydrogen for two operating points. At low load, numerical investigations show that hydrogen enhances the maximal combustion speed and the flame growth just after the spark which is a critical aspect of combustion with diluted mixtures. The flame front propagation is also more isotropic when supported with hydrogen. At mid load, hydrogen improves the combustion speed and also extends the auto-ignition delay times resulting in a better knocking resistance. A maximal indicated efficiency of 48.5% can thus be reached at λ = 2 thanks to an optimal combustion timing.

Effect of Combustion Characteristics on Knocking in a Direct Injection Turbo-Charged Gasoline Engine

Experimental study on knocking characteristics in a direct injection turbo-charged gasoline engine was carried out. The thermodynamic analysis was conducted to investigate effects of the combustion phasing and the burning rate on the knocking behavior. The localization of knock events and the characterization of the early flame kernel propagation were conducted with the fiber optic sensor. The advanced combustion phasing and the slower combustion speed generally increased the knocking probability. However, not only quasi-dimensional thermodynamic combustion characteristics but also the spatial parameter such as the flame propagation direction significantly affected the knocking occurrence. From the fiber optic sensor test results, knocking onset location was found to be closely correlated with the flame propagation direction and mainly observed in the opposite side to the main flame propagation direction. The flame propagation direction leaning to the exhaust side was identified to be favorable for the knocking mitigation because the end gas location on hotter exhaust side could be avoided. Engine tests for various squish designs and tumble port designs were implemented to study the effect of the in-cylinder flow, which significantly affects previously discussed knocking-related parameters. As a result, tumble and squish flow significantly increased combustion speed and advanced combustion phasing. Fuel consumption could be also reduced due to suppressed knocking combustion. In addition, new tumble port design enabled the flame propagation to have favorable leaning direction.

Combustion Characteristics of Methane Direct Injection Engine Under Various Injection Timings and Injection Pressures

The performance of a methane direct injection engine was investigated under various fuel injection timings and injection pressures. A single-cylinder optical engine was used to acquire in-cylinder pressure data and flame images. An outward-opening injector was installed at the center of the cylinder head. Experimental results showed that the combustion characteristics were strongly influenced by the end of injection (EOI) timing rather than the start of injection (SOI) timing. Late injection enhanced the combustion speed because the short duration between the end of injection and the spark-induced strong turbulence. The flame propagation speeds under various injection timings were directly compared using crank-angle-resolved sequential flame images. The injection pressure was not an important factor in the combustion; the three injection pressure cases of 0.5, 0.8, and 1.1 MPa yielded similar combustion trends. In the cases of late injection, the injection timings of which were near the intake valve closing (IVC) timing, the volumetric efficiency was higher (by 4%) than in the earlier injection cases. This result implies that the methane direct injection engine can achieve higher torque by means of the late injection strategy.

On the Supersonic Combustion of Hydrogen around a Conical Obstacle Considering Variable Specific Heats with Application to Scramjets

One proposes a combined analytical-numerical method for the supersonic combustion around a conical obstacle, considering variable specific heats with temperature. One important aspect is to avoid the dissociation what is not possible if normal detonation waves (of Chapman-Jouguet type) occur. The Clarke model where the detonation wave is separated in a shock wave and a deflagation wave is able to reduce the temperature. Here conical waves are used. In order to characterize the combustion speed and intensity, new parameters are proposed. A comparison with the Chapman-Jouguet combustion is also presented.

Experimental Study on Combustion Characteristics of LPG and Gasoline

Experiments were separately carried out on Liquefied Petroleum Gas (LPG) and gasoline as fuel for a spark ignition (SI) engine. According to the indicator diagram and the calculation of corresponding heat release, combustion characteristics of the two fuels were analyzed. The results showed that using LPG would lead to 7.64% power reduction and a little peak pressure reduction when the structures and ignition advance angle of the engine were remained. At rated speed and full load, the power of engine fueled with gasoline reaches the maximum when the excess air ratio is 0.90 and 0.76 fueled with LPG; when comparing the maximum power and specific heat consumption at different excess air ratios, we can see that the change of excess air ratio has a greater effect on the engine fueled with gasoline than that fueled with LPG; the specific heat consumption of both fuels decrease with the increase of load. Besides, under the same Фa, LPG has a shorter combustion delay period, faster combustion speed and shorter combustion period than gasoline.