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The quenching of a heated aluminum alloy plate with a spatial temperature gradient by water jet impingement was experimentally investigated to examine the effect of the liquid mass flow rate and liquid jet velocity by varying the nozzle diameter. The behavior of the liquid film formed by jet impingement was observed by high-speed imaging, and the temperature profile of the test plate was measured by infrared imaging. In addition, the surface heat flux and the amount of the heat removal, from the test plate to the liquid film, were calculated by inverse heat conduction analysis to investigate the heat transfer characteristics between the liquid film and test plate and to estimate the mass fraction of the injected liquid contributing to cooling. Results indicated that the wetting front propagation was affected by the mass flow rate, rather than by the liquid jet velocity. From the estimated results obtained by inverse heat conduction analysis, it was found that the values of the maximum heat flux, whose position lay near the wetting front, were almost the same under the same mass flow rate condition even though the liquid jet velocity was about 2.5 times different. In addition, from the estimation of the amount of heat removal, it was found that about 90% of the injected liquid was splashed away from the test plate without evaporation.

Pulse firing is one of the major operation modes of bipropellant thrusters for the attitude control of small-scale spacecrafts. In the pulse-firing mode, the operational range of the thruster depends on the deterioration of liquid film cooling performance. Because cooling performance is determined by the balance of heat removed by the liquid film and transferred to the manifold, the behavior and heat transfer characteristics of liquid films under the intermittent injection of liquid jets must be understood to enable a wider range of operational patterns. We conducted cooling tests on a superheated metal plate via the pulsed injection of a liquid jet for better understanding of the pulsed cooling process. Different injection patterns, including continuous injection, with the same injection quantity were examined on two types of metal plates (aluminum alloy and copper), because the thermal properties of metal plates affect both the heat transfer characteristics of the liquid film and temperature rise of the plate during the inter-pulse duration. The cooling process was evaluated based on the evolution of the liquid film on the metal plate and rear-side temperature of the metal plate. The evolution and temperature were simultaneously visualized using a high-speed camera and infrared camera, respectively. To link the liquid film state to the heat transfer process, the temperature and heat flux on the cooled surface were estimated by solving the inverse problem of three-dimensional transient heat conduction. The results indicate that the wetting front position corresponds to the position of the maximum temperature gradient. Additionally, the residual liquid film is consumed through the evaporation and the droplet dispersion related to the nucleate boiling. The effects of thermal inertia and diffusivity of the metal plate highlight the differences in the amount of heat removed by the liquid film. The heat removed by the liquid film during pulsed cooling exhibited a peak and was higher than that removed by continuous injection on the aluminum alloy plate. Less heat was removed under low-duty-cycle conditions, and the amount of heat removed by the liquid film was lower than that removed by continuous injection on the copper plate.

形態: カラー図版あり, Physical characteristics: Original contains color illustrations, Accepted: 2020-06-24, 資料番号: PA2110026000

To understand the soot formation characteristics in a pulverized coal flame with a swirling flow, simultaneous imaging of Mie scattering of coal particles and laser induced incandescence (LII) of soot were performed in this study. The pulverized coal flame was stabilized by a hydrogen diffusion pilot flame. The characteristic structures of soot formation in the pulverized coal flame with a swirling flow were analyzed based on a comparison of the experimental results and two-dimensional numerical simulation in the mixing region of coal particles and the oxidizer. The interactions between coal particle clouds and soot formation are discussed in detail. The results clearly show that the averaged radial dispersions of scattering signals from coal particles and of the LII signals from soot are overlapped. The overlapping region appeared nearby the nozzle exit due to the turbulent mixing and the high temperature region formed by swirl-induced recirculation flow. This overlapping region radially expands with increasing the height from the burner. Additionally, the characteristic areas of soot formation were observed in the results of simultaneous imaging of Mie scattering and LII. These areas are 1) streaky soot formation areas around the particle clouds, 2) soot formation areas inside of the particle clouds and 3) soot formation areas around the large coal particles.

A reduced kinetic model for the combustion of n-heptane, i-octane, n-cetane and heptamethylnonane was developed based on a prior model designed for use with a primary reference fuel consisting of n-heptane and i-octane. The present model, which can be easily employed in conjunction with a conventional computational fluid dynamics code, contains 59 chemical species and 96 reactions. Predicted ignition delay times under high pressure and temperature conditions were generated using this new kinetic model and compared with those obtained from full kinetic models. The results indicate that the general trends exhibited by the ignition delay times as temperature and pressure are varied are accurately predicted with this reduced model. The present model was also combined with a commercial computational fluid dynamics code and used to simulate the ignition of a diesel spray at high pressure and temperature. Finally, the effects of the cetane number of the fuel on the ignition process were investigated.

The main objective of this study is to evaluate the characteristics of combustion that combine premixed charge compression ignition (PCCI)-based combustion with conventional mixing controlled combustion. In this type of combustion, it is supposed that the combustion duration is shortened due to the synchronization of the timing of two types of combustions. In addition, the cooling loss caused by spray impingement is expected to decrease by the reduction of the proportion of mixing controlled combustion. In this study, the effect of injection pressure, injection timing, and split injection on thermal efficiency and emissions were investigated in order to determine the appropriate injection parameters for PCCI-based combustion to realize the proposed combustion concept., 2019 JSAE/SAE Powertrains, Fuels and Lubricants

Numerical calculations were carried out to investigate the formation of a fuel–air mixture as well as ignition and combustion processes associated with a diesel spray impinging on a wall. This was performed by modeling the spray formed by injecting n-heptane into a constant-volume vessel under high temperature and pressure, with the fuel droplets described by a discrete droplet model. The flow and turbulent diffusion processes were calculated based on the large eddy simulation method to simulate the formation of a local non-homogeneous mixture and the accompanying heat release. The flame structure and heat transfer to the wall during impingement were also assessed. The results show that heat transfer to the wall is increased in the peripheral region around the stagnation point, as a result of the high temperature and thin boundary layer. Conversely, in the outer region, the heat transfer decreases as the boundary layer becomes more developed.

In previous study, post injection has shown a significant benefit in the reduction of soot emissions. Among them, the close post injection which only has short dwell between the main injection is supposed to be able to increase the thermal efficiency. The reduction of the cooling loss due to the main flame impingement is considered as the reason to the increase of thermal efficiency. However, there is a lack of study related to the influence of post injection timing and quantity on the combustion characteristics. Therefore, in this study, the engine performance and emission characteristics of injection strategy with close post injection was investigated. The post injection timing was modified from near zero interval to around 4.5°CA from the end of main injection. In addition, the post injection quantity was modified from 3, 9, to 15 mm3/cycle and the intake pressure was modified from 170, 200, to 220 kPa while maintaining the total injection quantity at 39 mm3/cycle. In order to clarify the mechanism of cooling loss by applying post injection and the effect of injection dwell to the cooling loss and combustion characteristics, an optical engine was used to observe the combustion process. As a result, a certain dwell is needed to fully exploit the effect of cooling loss reduction by post injection.

Previously, some efforts were made to investigate the effect of combining premixed charge compression ignition (PCCI) combustion with conventional mixing controlled combustion using two injectors for single cylinder. In this experiment, the PCCI combustion was introduced by a sub injection fixed at early stage and the conventional diesel combustion was introduced by main injection starts near top dead center (TDC). The self-ignitability of sub injection fuel was modified by blending n-heptane and isooctane. Therefore, the ignition delay of PCCI combustion was extended to overlap with conventional diesel combustion near TDC by increasing the isooctane volume percentage in sub fuel. By overlapping PCCI and conventional diesel combustion, the cooling loss could be reduced. Later, the combustion and emission characteristics of the combined combustion strategy was examined. The experimental results showed that with larger PCCI combustion ratio at the fixed load, the degree of constant volume (DCV) increased. At the same time, the cooling loss was decreased slightly.

This study aims to utilize high-pressure split-main injection for improving the thermal efficiency of diesel engines. A series of experiments was conducted using a single-cylinder diesel engine under conditions of an engine speed of 2, 250 rpm and a gross indicated mean effective pressure of 1.43 MPa. The injection pressure was varied in the range of 160–270 MPa. Split-main injection was applied to reduce cooling loss under the condition of high injection pressure, and the split ratio and the number of injection stages were varied. The dwell of the split main injection was set to near-zero in order to minimize the elongation of the total injection duration. As a result, thermal efficiency was improved owing to the combined increase in injection pressure, advanced injection timing, and split-main injection. According to the analysis of heat balance, a larger amount of the second part of the main injection decreased the cooling loss and increased the exhaust loss. Computational fluid dynamics calculations were performed to reveal the causes of the lower cooling loss; however, the results could not capture the experimental trend when using an ordinary spray cone angle. While using a wider spray angle for the second part of main injection, the calculated trend improved. The total cooling loss depends on the balance between the cooling losses by the first and second main sprays., International Powertrains, Fuels & Lubricants Meeting

The direct-injection-premixed charge compression ignition–based combustion process with a high exhaust gas recirculation ratio and early injection timing is simulated using a Reynolds-averaged Navier–Stokes–based commercial computational fluid dynamics code with a nonhomogeneous mixture auto-ignition combustion model. In addition, the formation processes of nitrogen oxide (NO), carbon monoxide (CO), and unburnt hydrocarbon are calculated. The calculation results are compared with the experimental data. According to the calculation results, the formation processes of NO, CO, and hydrocarbon are discussed in relation to the spray development and ignition point. Furthermore, the combustion process of two-stage injection is also calculated. The result shows that the combustion process is described well by this model except in the case where auto-ignition occurs in the squish area. Additionally, the relationship between the combustion process and the mixture distribution is clarified. The main origins of the unburnt hydrocarbon and CO emissions are located in the center region of the combustion chamber, where the mixture becomes excessively lean and low in temperature.

The factors affecting knock resistance of fuels, including hydrogen (H2), ethane (C2H6), propane (C3H8), normal butane (n-C4H10), and iso-butane (i-C4H10), were determined using modeling and engine operation tests with spark-ignition gas engines. The results of zero-dimensional detailed chemical kinetic computations indicated that H2 had the longest ignition delay time of these gaseous fuels. Thus, H2 possessed the lowest ignitability. Results of engine operation tests indicated that H2 was the fuel most likely to result in knocking. The use of H2 as the fuel produced a temperature profile of the unburned gas compressed by the piston and flame front that was higher than that of the other fuels due to the high specific heat ratio and burning velocity of H2.The relation between knock resistance and secondary fuel ratio in methane-based fuel blends also was investigated using methane (CH4) as the primary component, and H2, C2H6, C3H8, n-C4H10, or i-C4H10 as the secondary components. When the secondary fuel ratio was small, the CH4/H2 blend possessed the lowest knocking tendency. But as the secondary fuel ratio increased, the CH4/H2 mixture possessed a greater tendency to knock than did CH4/C2H6 due to the high specific heat ratio and burning velocity of H2. These results indicate that the knocking that can occur with gaseous fuels is not only dependent on the ignitability of the fuel, but it also the specific heat ratio and burning velocity.Copyright © 2015 by ASME

Numerical calculation based on large eddy simulation was carried out to investigate mixture formation process in a spray formed by injecting n-heptane into a constant volume vessel under high-temperature and high-pressure conditions. Liquid phase of fuel was described by discrete droplet model. The results show that the shape of spray is similar to that of visualized image and spray tip penetration corresponds well to experimental results. In addition, distributions of fuel concentration and local non-homogeneous distribution were discussed by comparing the calculation results with the mixture distributions measured using planer laser induced fluorescence technique. The local distributions were well described except around downstream spray boundary. Calculations were also carried out for lower injection pressure condition and smaller nozzle orifice diameter condition. Although fuel concentration in a spray does not quantitatively reproduce the experimental results, the effects of the injection conditions qualitatively agreed with the experiments. Furthermore, ignition and combustion processes were investigated using Schreiber's model for calculating the progress of oxidation reactions.

Distributions of velocity and concentration of turbulent gas jets with various densities from helium to carbon dioxide against ambient air are measured by using particle image velocimetry and laser induced fluorescence methods. The turbulent transport of the jet fluid is directly investigated to analyzing the distributions of jet-fluid concentration and its vortex motion. The result shows that the self-similarity exists between profiles of scalar flux and Reynolds stress along the radial direction. Furthermore, several subgrid scale scalar-flux models for large eddy simulation are discussed. Based on the scattering plots of model values of subgrid scale scalar-flux against the measured values, the characteristics of each model are basically similar for every density conditions. Also, the Favre-averaged scale similarity model performs well for wide various densities.

To achieve further reductions in fossil fuel consumption and carbon dioxide (CO2) emissions, the transportation sector will need to assume a key role. Based on the BLUE Map scenarios for 50 % reduction in CO2 emissions by 2050 in the Energy Technology Protocol 2010 of the International Energy Agency, conventional engine vehicles and hybrid electric vehicles (HEVs)—including plug-in hybrid electric vehicles (PHEVs)—are expected to account for 90 % of the market and will still account for 50 % of the market by 2050. This means that it is important that thermal efficiency of the internal combustion engine (ICE) be increased. Research and development into high-efficiency ICEs has been progressing in Japan, Europe, and the United States. In this paper, current research status and future prospects of ICEs and HEVs (PHEVs) are described.

The flow and mixing process of unsteady jets are fundamentally analyzed by large eddy simulations. The effects of nozzle velocity and turbulence intensity on the turbulent eddy structure and mixing process between the nozzle fluid and ambient fluid were investigated. The results show that a toroidal-shaped vortex, which emerges around the jet tip, primarily accelerates the entraining flow. Also, increasing the turbulence intensity in the nozzle encourages mixing in the jet without changing the jet-contour. Furthermore, when the rise-up time of the initial nozzle velocity is elongated, turbulent mixing is suppressed. © 2007 Wiley Periodicals, Inc. Heat Trans Asian Res, 36(5): 303–313, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.20158

The factors affecting knock resistance of fuels, including hydrogen (H2), ethane (C2H6), propane (C3H8), normal butane (n-C4H10), and iso-butane (i-C4H10), were determined using modeling and engine operation tests with spark-ignition gas engines. The results of zero-dimensional detailed chemical kinetic computations indicated that H2 had the longest ignition delay time of these gaseous fuels. Thus, H2 possessed the lowest ignitability. Results of engine operation tests indicated that H2 was the fuel most likely to result in knocking. The use of H2 as the fuel produced a temperature profile of the unburned gas compressed by the piston and flame front that was higher than that of the other fuels due to the high specific heat ratio and burning velocity of H2. The relation between knock resistance and secondary fuel ratio in methane-based fuel blends also was investigated using methane (CH4) as the primary component, and H2, C2H6, C3H8, n-C4H10, or i-C4H10 as the secondary components. When the secondary fuel ratio was small, the CH4/H2 blend possessed the lowest knocking tendency. But as the secondary fuel ratio increased, the CH4/H2 mixture possessed a greater tendency to knock than did CH4/C2H6 due to the high specific heat ratio and burning velocity of H2. These results indicate that the knocking that can occur with gaseous fuels is not only dependent on the ignitability of the fuel, but it also the specific heat ratio and burning velocity.

A series of experiments was conducted using a single-cylinder small-bore (85 mm) diesel engine to investigate the smoke-reduction effect of post injection by varying the number of injection nozzle orifices and the injection pressure. The experiments were performed under a constant injection quantity condition and under a fixed NOx emission condition. The results indicated that the smoke emission of six-hole, seven-hole, and eight-hole nozzles decreased for advanced post injection, except that the smoke emission of the 10-hole nozzle increased as the post injection was advanced from a moderately late timing around 17° ATDC. However, the smoke emission of the 10-hole nozzle with a higher injection pressure decreased for advanced post injection. These trends were explained considering the influence of the main-spray flames on post sprays based on CFD simulation results., JSAE/SAE 2015 International Powertrains, Fuels & Lubricants Meeting

The flow of a high-speed unsteady jet is analyzed using computational fluid dynamics for an incompressible flow with the k–e turbulence model. The pseudo-nozzle concept is applied to the inlet condition with a large pressure gradient. The results show that the time history of the jet development agrees with the experimental data for methane and hydrogen fuels. In addition, the effect of the injection condition on the development of the jet tip is well described with this model. Furthermore, the effects of inlet conditions of the turbulence intensity and scale on the flow are investigated. © 2006 Wiley Periodicals, Inc. Heat Trans Asian Res, 36(1): 1– 12, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.20141