Air Mass Flow Rate Research Articles

Determining The Ratio Of Pressure And Compressor Air Mass Flow Rate To Generate Thrust

Missiles are strategic defense equipment that have a high deterrent effect in the national defense system because they have high destructive power, high precision, and can be launched remotely. With the above characteristics, the missile is a high-tech product, and it still needs a lot of engineering effort to master the technology, especially the propulsion / propulsion system technology which is mostly in the form of turbojet engines. With the above background, this study designs and analyzes one of the main components of the missile propulsion system, namely the compressor impeller. This study analyzes the pressure ratio and mass flow rate of compressor air whose values are used to obtain the impeller design of a small turbojet engine compressor on a surface-to-surface cruise missile propulsion system. The method used is analytical method. The conclusion of the study is that the combination of a compressor pressure ratio of 4 and an air mass flow rate of 2.5 kg/s can produce a target thrust of 1,300 N, and the diameter of the turbojet engine is smaller than the maximum allowable space diameter of 270 mm.

Heat Release Rate from a Two-Phase Kerosene/Air Flame Using Chemiluminescence

An experimental method based on chemiluminescent measurements is developed to determine the heat release rate produced by a two-phase flow kerosene/air flame. This quantity is known to be proportional to the air mass flow rate and the equivalence ratio. Experimental studies are carried out downstream of a liquid fuel injector used in aeronautical combustion chambers. The chemiluminescent spectra of the flame are analyzed for different air mass flow rates and equivalence ratios ranging from 0.4 to 0.71 in the steady-state flame configuration. The broadband background emission due to emission (where indicates an electronically excited specie) and soot radiation is first evaluated. Then, the analysis of the chemiluminescent emission from , , and indicates that the may be used to determine both the instantaneous equivalence ratio and the air mass flow rate. An example of the application of this method to measure fluctuations in the heat release rate induced by acoustic excitation of the flame is shown.

Performance Optimization of Hybrid Draft Biomass Cookstove Using CFD

ABSTRACT The term “hybrid draft biomass cookstove” (HDBC) refers to a stove that employs both natural and forced drafts for its primary and secondary air supply. The HDBC optimization analysis is carried out in this work using computational fluid dynamics (CFD), considering the effect of forced draft secondary air mass flow rates to achieve the optimum (lower emissions and higher efficiency) HDBC performance. The analysis includes combustion and soot modeling to evaluate the thermal and emission performance of the stove. The CFD results are validated against the experimental data obtained from the water boiling test (WBT 4.2.3). The extremely low or high secondary air mass flow rate degrades the stove’s performance; hence, its optimization is essential. The optimal mass flow rate identified in this investigation was 0.017 kg/s, at which the thermal and emission performances of HDBC were evaluated. An eddy dissipation model is employed to simulate biomass combustion, considering the reaction kinetics of wood volatiles reacting with oxygen, and a one-step soot model is used to predict soot formation. The combustion model agreed well with the experimental data for efficiency and temperature, with an average deviance of 10% and 20%, respectively. However, it significantly overestimated CO emissions by 81% and achieved Tier 4 performance in simulation as opposed to Tier 0 in the experiment. The PM2.5 emissions were under predicted by the soot model, but both the CFD and the experiment results achieved Tier 4 performance as per the World Health Organization (WHO) standards. Hence, a one-step soot model was found to be effective in predicting soot formation.

Optimizing Pressure Prediction Models for Pneumatic Conveying of Biomass: A Comprehensive Approach to Minimize Trial Tests and Enhance Accuracy

This study investigates pneumatic conveying of four different biomass materials, namely cottonseeds, wood pellets, wood chips, and wheat straw. The performance of a previously proposed model for predicting pressure drop is evaluated using biomass materials. Results indicate that the model can predict pressure with an error range of 30 percent. To minimize the number of trial tests required, an optimization algorithm is proposed. The findings show that with a combination of three trial tests, there is a 60 percent probability of selecting the right subset for accurately predicting pressure drop for the entire range of tests. Further investigation of different training subsets suggests that increasing the number of tests from 3 to 7 can improve the probability from 60% to 90%. Moreover, thorough analysis of all three-element subsets in the entire series of tests reveals that when considering air mass flow rate as the input, having air mass flow rates that are not only closer in value but also lower increases the likelihood of selecting the correct subset for predicting pressure drop across the entire range. This advancement can help industries to design and optimize pneumatic conveying systems more effectively, leading to significant energy savings and improved operational performance.

Conversion of cud and paper waste to biochar using slow pyrolysis process and effects of parameters

A series of laboratory studies were undertaken in Gondar to explore the effects of temperature, air mass flow rate, heating rate, and residence duration on cud and waste paper char yields in slow pyrolysis. Cud and waste paper were burned at a low pyrolysis temperature to generate biochar (167 °C). The rate of decomposition depends on the feedstock and the process conditions. The biochar yield is mostly governed by the applied regulated temperature and airflow rate, according to the data. During the experiment, the main airflow rate delays the pyrolysis process.The temperature rises when both the primary and secondary air inlets open at the same time, resulting in lesser biochar output. The experiment was carried out at a slow pyrolysis temperature of 167 °C, with 15% biomass moisture, 60% humidity, and a 0.35–1.5 kg/s air mass flow rate. At this temperature, 30 kg of feedstock, cup, and paper in the reactor generate 10 kg–23kg and 10–20 kg of biochar, respectively, at a 0.35 m/s airflow rate. As the airflow rate increases within the restricted values, a temperature gradient appears and tends to increase. However, as the pyrolysis temperature and airflow rate rise, the biochar yield decreases.

Numerical investigation of hydrogen addition effects to a methane-fueled high-pressure combustion chamber

To get a general understanding of hydrogen fuel usage in a real-condition high-pressure industrial gas turbine burner operating at 15 atm pressure, the effects of hydrogen addition to methane fuel are studied numerically. Methane-hydrogen premixed fuel-lean flame is investigated while hydrogen is substituted for methane at a fixed fuel and air mass flow rate at the burner inlet. Steady-state reacting and swirling flow equations (RANS) are solved using the standard k−ε model as the turbulence model. A detailed methane combustion mechanism GRI 2.11 is used to simulate methane-hydrogen combustion with Finite Rate formulation more accurately. Temperature and axial velocity variation and important pollutant species emissions such as CO, CO2, and NOx were investigated at the combustion chamber exit. Flame shape, flow pattern, and flame location variation with hydrogen addition were studied due to hydrogen flashback limits. The hydrogen addition leads to higher temperatures inside the burner and the hot zone inside the combustion chamber extends and moves toward the fuel inlet. Flow structure including recirculation zones change with hydrogen addition. CO emission increases by hydrogen addition to the fuel mixture near the burner exit while CO2 mass fraction is reduced. A significant increase in NO mass fraction with hydrogen addition was observed near the burner exit due to higher temperature.

Investigation of Thermo-Hydraulic Performances of Artificial Ribs Mounted in a Rectangular Duct

This research investigates the fluid flow characterization and thermohydraulic performances (THP) of rib surfaces, using computational and experimental methods. ANSYS computational fluid dynamics (CFD) software was used to predict and validate the findings in the experimental setup. Artificial rib surfaces, including polygonal and forward trapezoidal-shaped ribs, were placed in the absorber plate at different relative pitch distances (p/e) = 6.7, 10, 13.4 and relative height (e/d) = 20, and the mass flow rate of air (working fluid) varied at Reynolds numbers ranging from 2000 to 20,000. According to the validation results, the RNG renormalization k-ε model was selected for the investigation. The results show that strong turbulence occured closer to the wall surface and behind the rib surface, enhancing thermal performances due to the sharp edge shape of the rib. A polygonal rib with a pitch distance of p/e = 6.7 achieved a higher Nusselt number (Nu) and thermohydraulic performance of 2.95 at Re 4000. An empirical correlation between the Nusselt number (Nu) and friction factor (f) was developed using linear regression analysis and was compared with the predicted values. The comparison results show a close range of ±8% between the experimental and predicted values.

Thermal performance optimization of rectangular cavity receiver for cross linear concentrating solar power system

ABSTRACT A thermodynamic analysis was performed on a newly developed concentrated solar power (CSP) technology known as the Cross-Linear (CL), which addresses the issue of cosine loss in conventional CSP technology. The analytical model has been developed and validated using experimental data collected at the experimental site situated in Bhopal, India. The analysis was performed under direct normal irradiance of 775 W/m2 with the key objective to determine the optimum inlet condition of the heat transfer fluid (HTF) considering three optimization parameters: HTF outlet temperature, energy, and exergy efficiency of the receiver. Also, the exergy of the solar field is investigated depending on the available solar irradiation throughout the day for three different configurations of the heliostat field. After a comprehensive analysis of the results, the optimal air inlet temperature range was observed to be between 373 and 423 K, and the optimal air mass flow rate was overserved to be 0.0925 kg/s (333 kg/h), which provides energy and exergy efficiency values within 50% to 60% and 28% to 34%, respectively. The maximum electrical exergy efficiency for 30 kW plant capacity is observed to be around 70% at solar noon with a cosine factor of around 0.9 for 4-hour duration.

Assessment of thermal and environmental benchmarking of a solar dryer as a pilot zero-emission drying technology

Food drying is a highly energy intensive process and therefore significantly contribute to carbon emission. Although solar air dryers are considered renewable, they are not fully emission free as conventional energy from grid is required to run the fan or blower. The solar air efficiency as well as fan power requirements are influenced by the mass flow rate of air, and therefore flow rate is essential parameter for evaluating solar air dryer performance in terms of thermal, drying and environmental parameters. It is essential to develop a framework to evaluate critical mass flow rate by considering the optimum thermal, drying, and environmental performance for benchmarking of zero-emission solar air dryer. However, such a framework is currently lacking. To address this issue, a novel study was conducted using V-groove double pass solar air heater (SAH) to experimentally analyse thermal, drying and environmental parameters to develop a methodology for zero emission solar air dryers based on critical flow rate for fan power consumption. The experiments were conducted at five different flow rates (0.021, 0.031, 0.041, 0.051, and 0.061 kgs−1). The maximum thermal efficiency achieved was 74.89% at 0.061 kgs−1. However, the average COP, average exergy efficiency, moisture ratio, and CO2 mitigation had optimum results at 0.041 kg/s mass flow rate as fan power consumption was reduced by 16% compared to 0.061 kgs−1. The critical flow rate evaluation is useful for predicting and minimising power consumption and progress towards zero emission system by using photovoltaics in future systems. The successful implementation of the proposed method can substantially contribute to the industrialisation and cutting of emissions of solar air heaters for drying applications.

Thermal performance of a hybrid solar dryer through experimental and CFD investigation

AbstractSolar drying comes under clean energy technology that aims to dry food products hygienically. The present work discusses the development of an energy‐efficient and cost‐effective hybrid‐type solar dryer for drying 15 kg of food products. Experiments and CFD modeling of the solar drying system have been carried out for drying tomato slices. The maximum efficiency of the collector has been obtained as 74.1% and 66.96%, respectively with and without using exhaust hot air recirculation. Performance indicators such as convective heat transfer coefficient, overall loss coefficient, drying efficiency, and collector efficiency factor have been obtained as 7.743685 W/m2°C, 5.94189 W/m2°C, 32.89%, and 0.987%, respectively. The coefficient of determination (R2) is calculated as 0.9863, 0.9919, and 0.9755 for the first, second, and third day, respectively, representing a higher order of fit of getting a performance evaluation of the collector. A p‐value is obtained as 0.49375 (>0.05) from a paired sample t‐test signifying no statistical significance difference between the predicted and actual experimental results of collector efficiency. For a constant mass flow rate of air, the maximum temperature inside the drying chamber and wall radiative heat flux obtained from experiments and CFD simulation are in good agreement, thus satisfying the validation. Further, the dryer can be used during the night time by using an electric coil producing a satisfactory drying effect. It is lightweight and easily portable to capture maximum solar radiation.Practical applicationsThe present solar dryer is most suitable for drying applications in food processing industries due to the clean and hygienic process of drying. It is easily portable to any location to capture maximum solar radiation. It is lightweight and has low construction, and maintenance costs. It is the most efficient and fast drying compared to open sun drying and can be used for large‐scale drying in industrial applications. The present study is about CFD simulations of the solar dryers for drying 5 kg of tomato slices. The drying efficiency has been increased by utilizing exhaust hot air circulation. Both the simulation and experimental results have been validated and further dryer has been used during night time by using an auxiliary heating element.

Theoretical Study of a Closed-Cycle Evaporation System for Seawater Desalination

This paper presents a numerical study of a closed-cycle evaporation system for the desalination of seawater. The system couples the condensing end of a heat pump with a humidifier, where the air is dehumidified in the heat pump evaporator. First, the mechanism of action of the closed-cycle evaporation system was analyzed from the perspective of heat transfer, and the control equations for the heat and mass transfer of the system were investigated. In addition, a mathematical model of the system was developed and validated. The influence of several important parameters of the air and seawater entering the system on the system’s performance under the design conditions was investigated numerically. The parametric analysis showed that the effect of the seawater mass flow rate on the system’s productivity was not significant. As the air mass flow rate increases, the freshwater production rate increases and then decreases. The output ratio (GOR) of the system was estimated and found to be competitive with other reported HDH systems.

Thermal performance evaluation of a compact two-fluid finned heat exchanger integrated with cold latent heat energy storage

To alleviate the mismatch between thermal energy supply and demand, the use of latent heat thermal energy storage of phase change materials is a reliable and effective solution in thermal systems. The present work aims to introduce an innovative finned-plate air-liquid heat exchanger with phase change material partially embedded in the fins' gap providing airside cooling by thermal energy storage during coolant shutdown periods. The thermal performance and accompanying phase change process are studied using a three-dimensional computational fluid dynamic approach. The developed model is validated with corresponding experimental data at the same geometry and operating conditions. The system performance is examined time-dependently considering the charging/discharging processes of the phase change material. The effect of air mass flow rate variation is studied, and the results are discussed in terms of fluids temperature, heat transfer rates, and the phase change material phase transition process. The results demonstrate that the heat exchanger stores excess thermal energy during the charging process, which is later discharged for air cooling during demand periods. It is observed that the use of phase change material provides a cooling load of 188 kJ and over 9 min of extra cooling time for the airside in the discharging process. The share of latent heat transfer in the discharging process is calculated at an average of 54% of the total heat transfer. Obtained results reveal that increasing the air mass flow rate can reduce the rate of discharged cold thermal energy and cooling time. The presented thermal management system offers a unique solution to manage passenger thermal comfort in hybrid and electric vehicles with a start-stop function. The introduced system could provide efficient cabin air cooling and enable effective energy savings during short periods of engine shutdown.

Effects of carbon nanodots coating and airflow rate on the thermal efficiency of flat plate collector

ABSTRACT The application of nanoparticle coating in a collector could resolve the issues of lesser heat transfer rate and lower thermal efficiency associated with the flat plate collector (FPC). In this study, carbon nanodots (CNDs) synthesized from fish scales wwere coated over the black paint coating to enhance the thermal efficiency of FPC. The effect of various concentrations (0, 0.1, 0.2, and 0.5%w/v) of CND coatings and mass flow rates of air (0.011 kg/s (natural convection) and 0.015, 0.029, and 0.044 kg/s (forced convection)) on the collector outlet air temperature and efficiency of the FPC were evaluated with a control (black paint). Solar radiation ranged from 382 to 913 W/m2 on the experimental days, and the atmospheric temperature and relative humidity values varied from 26.2 to 34.8°C and 50–72%, respectively. Fourier transform infrared spectroscopic studies of absorber plate coating revealed that the CNDs interacted with the black paint surface through phenolic OH, C=O, and NH mainly by hydrogen bonding. It was observed that the exit air temperature of the collector varied from 55 to 65°C. The thermal efficiency of 59.97%, 62.72%, 71.87%, and 67.75% was obtained for control (black-paint), 0.1%, 0.2%, and 0.5% CNDs coating, respectively, at the airflow rate of 0.044 kg/s. The coating of 0.2% CNDs recorded a maximum thermal efficiency of 71.87% at 0.044 kg/s. Overall, the CNDs coating on the absorber surface enhanced the thermal efficiency of the collector by 19.84% over the black paint-coated surface (control). It can be concluded from the study that CNDs coating resulted in enhanced outlet air temperature and improved thermal efficiency, which can be utilized for low-temperature applications like the drying of food materials.

Performance evaluation of a solar air heater with staggered/longitudinal finned absorber plate integrated with aluminium sponge porous medium

Solar air heaters are used to heat air for drying and space heating applications, however, the low heat transfer between air and absorber plate accounts for its low efficiency. In this paper, an experimental study of a staggered/longitudinal finned plate solar air heater (SLFPSAH) with a built-in aluminium sponge porous media as a sensible heat storage material is presented. The fins with the direction of airflow are arranged in a staggered manner by covering a length of 1.25 m, while the remaining 0.75 m is arranged with longitudinal fins. The parameters influencing the performance of the SLFPSAH are investigated with and without using a porous medium. These parameters include solar irradiance, the temperature difference of air through the heater, air temperature ratio, convective heat transfer coefficient, useful heat gain, daily energy efficiency, and exergy efficiency. Experiments are conducted under different air mass flow rates; namely, 0.0078, 0.01, 0.02, and 0.049 kg/s. The results revealed that the implementation of an aluminium sponge porous media over the absorber plate significantly increases the energetic and exergetic performances of the SLFPSAH. It is found that the average air temperature ratio, daily exergetic efficiency, and daily exergy efficiency of the SLFPSAH integrated aluminium sponge porous medium are about 11.52%, 3.97%, and 45.61% greater than that without the aluminium sponge porous medium, at airflow rate of 0.02, 0.049 kg/s, respectively. Moreover, the maximal increase in the convective heat transfer coefficient of the SLFPSAH integrated with aluminium sponge porous medium is more than 1.62 times that obtained with the SLFPSAH without porous media, at the same conditions. Thus, the SLFPSAH with an integrated aluminium sponge porous medium is an effective way to enhance the exergetic and energetic performances of solar air collectors for solar drying applications.

Effects of Radiator Angle and Sidepod Profile on Aerodynamic Performance of a Race Car

In Formula Society of Automotive Engineers (FSAE) cars engine heat management serves as an important factor for the performance of the vehicle. Therefore, a proper design of sidepod is crucial for optimal cooling of the engine since sidepods are designed to direct the airflow through the radiator. Also, since sidepods play an important role in the aerodynamic performance of the vehicle, factors such as drag and lift must also be considered along with the cooling of the engine. This paper brings forth the methodology carried out to design the sidepods effectively. First the optimal radiator angle is determined on which the maximum mass flow rate of air through the radiator core is observed. Angles are varied from 50, 70 and 90 degrees on various orientations with respect to the car. Fixing this radiator angle, various inlet and outlet areas of the sidepod are analyzed. Choosing the model with least drag and lift coefficient the sidepod is analyzed by sealing it at various sides. Finally, the effects of gills are also analyzed for better optimization of the sidepod. The models are designed in Solidworks and the CFD simulations are carried out in Simscale. Half car simulation is performed with symmetry conditions in order to reduce the cell count. The results of the analysis showed that the radiator angled forward with a diverging type sidepod yields in the better cooling of the engine.

Combined effect of solar intensity and air mass flow rate on inline spherical dimple based solar air heater during summer season

Experimental investigation was done in this study to compare the effectiveness of flat and inline spherical dimple engraved absorber plates solar air heater (SAH). During the summer, a SAH with a single glass cover, one pass, and two different types of absorber plates was evaluated on alternating days by taking readings from 9.30 a.m to 2.00p.m at an interval of 30 min. In order to conduct the investigation, the air mass flow rate (Ma) was raised from 0.0098 kg/s to 0.0520 kg/s (corresponding Re: 1861–10218) while solar intensities varied throughout the days. By increasing the Ma, various parameters were measured and different thermal characteristics were examined, such as the convective heat transfer coefficient, the blower’s power consumption, extracted power, effective power, efficiency, the heat gain factor, the heat loss factor, the SAH-efficiency factor, the averaged Nusselt number (Nu), and the averaged friction factor (f). The investigation reveals that with an increase in Ma, both flat and dimpled roughened SAH exhibit an increase in convective heat transfer coefficient, extracted power, instantaneous efficiency, heat gain factor, heat loss factor, and SAH-efficiency factor. However, the enhancement rate of inline dimple plate-solar air heater (IDP-SAH) due to engraved dimples is always higher than the flat plate-solar air heater (FP-SAH). Up to a particular Ma, both types of SAH have higher effective efficiencies. Thereafter effective efficiency decreases due to a significant increase in required pumping power. Comparing IDP-SAH to FP-SAH, the averaged Nu and the averaged f of IDP-SAH is 83.42% and 176.51% greater, respectively. In addition, the effective efficiency of IDP-SAH is 31.24% higher than the FP-SAH. The friction factor (f) starts to decline as the Ma increases. Even though the IDP-SAH and FP-SAH performance analyses were conducted on different days during the summer, IDP-SAH outperformed FP-SAH. The indentation of dimple on absorber plate helps in increasing surface area as well as helps in changing flow structure which is responsible for augmentation of heat transfer rate.

Prediction of the mean turbulence intensity with a thermodynamic model for CNG and gasoline fuels

Combustion is the main parameter that affects efficiency and exhaust gas emissions in internal combustion engines. In this study, the burning speed of gasoline and CNG were investigated quantitatively by calculating the mean value of turbulent consumption speed instead of qualitatively as is usually done. A three-zone quasi-dimensional thermodynamic model based on the measured cylinder pressure was created to calculate the mean value of turbulent consumption speed and turbulence intensity. The mass flow rate of air was kept constant in all experiments as much as possible, and the spark advance was kept constant at each relative air/fuel ratio. Thus, the effect of fuel and combustion chamber design on the consumption speed and turbulence intensity was directly determined. MR shape reached the highest consumption speed and turbulence intensity in all conditions. In the flat geometry, without any bowl, speed continuously decreased differently from the other designs. Natural gas burned clearly faster in the ultra-lean mixture. The increase in turbulence intensity has different effects on CNG and gasoline. The highest value of the mean turbulence intensity was calculated as approximately 3.4 m/s in the MR design. In the ultra-lean mixture, although the mass flow rate of air was constant, the mean value of the turbulence intensity changed in the same combustion chamber. Therefore, it has been determined that the combustion process affects the turbulence intensity. Using the quasi-dimensional thermodynamic model, mean values of the turbulent burning speeds and turbulence intensity might be calculated without having any optical observation and CFD analysis.

Effects of different physical properties of anthracite powder fuel on detonation characteristics of a rotating detonation engine

The rotating detonation engine (RDE) fueled by coal powder has attracted much attention because of its high thermal cycle efficiency. To explore the detonation characteristics of anthracite powder and further study the effects of particle size and morphology on them, a series of rotating detonation experiments with anthracite powder were carried out in a disk-shaped combustor. The experimental results show that the morphology of anthracite particles plays an important role in detonation. The addition of porous anthracite (PA) enhances the detonation intensity in the lean hydrogen–air, while flaky anthracite (FA) weakens it. The concentration rise of PA increases the detonation wave height, while FA does not have such an obvious effect on the height. The excessive addition of any anthracite powder increases the heat loss of the detonation, resulting in a decrease in detonation velocity. By comparing the detonation characteristics of 20-nm, 3-μm, and 40-μm PA, it is found that the detonation performance of 20-nm PA, which has strong agglomeration, has no significant advantages over the micron-sized PA. Among the three PA powders, 3-μm PA has the largest detonation intensity and velocity. The difference in engine performance caused by pulverized anthracite with different morphological characteristics is as follows: when the mass flow rates of coal, H2, and air are 6.7, 5.3, and 260 g/s, respectively, the specific impulse of 3-μm PA reaches 7.8 kN·s/kg, which is about 2.7 times higher than that of 5-μm FA. This research provides theoretical guidance for the powder fuel selection of the RDE.

Arrhenius type empirical ignition delay equations based on the phenomenology of in-cylinder conditions for wide operating ranges in modern diesel engines

Ignition delays were systematically measured in a DI diesel engine under wide ranging and various engine operating conditions, including engine speeds, fuel injection pressures, intake gas temperatures, intake gas pressures, and intake oxygen concentrations changed with EGR. Empirical equations to predict the ignition delay based on the Arrhenius equation with and without the Livengood-Wu integral and multiple regression analysis of the experimental results. The simple equation assuming constant conditions during the ignition delay without the Livengood-Wu integral can accurately predict the ignition delay. However, the lack of generality has remained as the fuel injection pressure is directly included in the Arrhenius equation which should contain only the chemical parameters. To improve the generality of the equation, the ignition delay was separated into the initial physical process of the fuel spray breakup and the following chemical process. The start of the Livengood-Wu integral was set at the breakup time of liquid fuel jet assuming that the chemical reactions do not occur before the fuel spray breakup, and that the physical factors are directly involved in the physical processes and indirectly in the chemical processes. The fuel spray tip dynamics based on Wakuri’s momentum theory was introduced to express the changes in the conditions in the fuel spray during the ignition delay. The ignition delay can be accurately predicted by the equation with the Livengood-Wu integral and six parameters, including the breakup time, the mass flow rates of air and fuel at the cross section of the spray tip, the oxygen partial pressure, the engine speed, and the averaged in-cylinder gas temperature. The empirical equation predicted longer ignition delays at high ignition pressure conditions, and the accuracy was improved by performing a multiple regression analysis separately at each fuel injection pressure, suggesting unknown factors varying with the fuel injection pressures.

Effects of backpressure on unstart and restart characteristics of a supersonic inlet

AbstractThe unstart phenomenon of supersonic inlets caused by backpressure is dangerous for aircraft during flights because it severely reduces the air mass flow rate through the engine. We used unsteady numerical simulations to evaluate the unstart and restart characteristics of a two-dimensional supersonic inlet during rapid backpressure changes. The effects of the depressurisation time and depressurisation value on the inlet flow characteristics and restart features are discussed. The results show that the depressurisation time affects the restart procedure when the back pressure drops from the inlet unstart value to the normal working state value. When the depressurisation time decreases, it becomes easier for the inlet to restart. However, the inlet cannot restart if the depressurisation time is too long. When the depressurisation time and value were large enough, a short buzz period occurred before the inlet restarted. Both the time and value of depressurisation affected the restart characteristics.