Relighting of jet engines at high altitudes is very difficult because of the high velocity, low pressure, and low tempera- ture of the inlet airflow. Successful ignition needs sufficient ignition energy to generate a ...Relighting of jet engines at high altitudes is very difficult because of the high velocity, low pressure, and low tempera- ture of the inlet airflow. Successful ignition needs sufficient ignition energy to generate a spark kernel to induce a so-called critical flame initiation radius. However, at high altitudes with high-speed inlet airflow, the critical flame initiation radius becomes larger; therefore, traditional ignition technologies such as a semiconductor igniter （SI） become infeasible for use in high-altitude relighting of jet engines. In this study, to generate a large spark kernel to achieve successful ignition with high-speed inlet airflow, a new type of multichannel plasma igniter （MCPI） is proposed. Experiments on the electrical char- acteristics of the MCPI and SI were conducted under normal and sub-atmospheric pressures （P = 10-100 kPa）. Ignition experiments for the MCPI and SI with a kerosene/air mixture in a triple-swirler combustor under different velocities of inlet airflow （60-110 m/s）, with a temperature of 473 K at standard atmospheric pressure, were investigated. Results show that the MCPI generates much more arc discharge energy than the SI under a constant pressure; for example, the MCPI generated 6.93% and 16.05 % more arc discharge energy than that of the SI at 30 kPa and 50 kPa, respectively. Compared to the SI, the MCPI generates a larger area and height of plasma heating zone, and induces a much larger initial spark kernel. Furthermore, the lean ignition limit of the MCPI and SI decreases with an increase in the velocity of the inlet airflow, and the maximum velocity of inlet airflow where the SI and MCPI can achieve successful and reliable ignition is 88.7 m/s and 102.2 m/s, respectively. Therefore, the MCPI has the advantage of achieving successful ignition with high-speed inlet airflow and extends the average ignition speed boundary of the kerosene/air mixture by 15.2%.展开更多
The utilization of graded Al powders offers the possibility to adjust the combustion performance of Al powders,while simultaneously safeguarding their energy properties.In this paper,a series of graded Al powder have ...The utilization of graded Al powders offers the possibility to adjust the combustion performance of Al powders,while simultaneously safeguarding their energy properties.In this paper,a series of graded Al powder have been incorporated into the typical Al@AP composites through the spray drying technique.The thermal behavior,ignition and combustion characteristics were comprehensively evaluated and compared.The experimental results showed that with the varying inclusion of the graded Al,the heat of reaction exhibited a significant change,ranging from 9090 J·g^(-1) to 11036 J·g^(-1),which was strongly dependent on the particle size of Al.The combination of Al with diverse range of particle sizes in graded configuration serves to significantly enhance the decomposition of AP,resulting in the disappearance of the LTD stage and a conspicuous decrease of at least 11.7℃ in the peak temperature of the HTD.Furthermore,the maximum burning rate achieved by the Al-3@AP composite was 33.6 mm·s^(-1),which was exactly twice as high as that of the graded Al-1@AP composite with the lowest burning rate.Diffraction peaks corresponding to unburned Al were detected in the condensed combustion products of Al-1@AP,and the combustion images clearly indicated an incomplete combustion tendency for this sample.In contrast,a well-designed gradation of Al powders,such as a combination of fine Al powders with a particle size below 5μm,has proven to be the most conducive to enhancing the combustion efficiency of the composites.展开更多
In this study,an artificial neural network(ANN)is developed to predict the performance of a spark-ignition engine using waste pomegranate ethanol blends.A series of experiments on a single-cylinder,four-stroke spark-i...In this study,an artificial neural network(ANN)is developed to predict the performance of a spark-ignition engine using waste pomegranate ethanol blends.A series of experiments on a single-cylinder,four-stroke spark-ignition engine yielded the data needed for neural network training and validation.70 percent of the experimental data was used to train the network using the feed-forward back propagation(FFBP)algorithm.The developed network model’s performance was evaluated by contrasting its output with experimental results.Input parameters included engine speed,ethanol blends,and output parameters included indicated and brake power,thermal,volumetric,and mechanical efficiencies.Training and testing data had regression coefficients that were almost identical to one.The research revealed that the ANN model can be a better option for predicting engine performance with a higher level of accuracy.展开更多
基金Project supported by the National Natural Science Foundation of China(Grant Nos.91541120,11472306,51336011,and 91641204)
文摘Relighting of jet engines at high altitudes is very difficult because of the high velocity, low pressure, and low tempera- ture of the inlet airflow. Successful ignition needs sufficient ignition energy to generate a spark kernel to induce a so-called critical flame initiation radius. However, at high altitudes with high-speed inlet airflow, the critical flame initiation radius becomes larger; therefore, traditional ignition technologies such as a semiconductor igniter （SI） become infeasible for use in high-altitude relighting of jet engines. In this study, to generate a large spark kernel to achieve successful ignition with high-speed inlet airflow, a new type of multichannel plasma igniter （MCPI） is proposed. Experiments on the electrical char- acteristics of the MCPI and SI were conducted under normal and sub-atmospheric pressures （P = 10-100 kPa）. Ignition experiments for the MCPI and SI with a kerosene/air mixture in a triple-swirler combustor under different velocities of inlet airflow （60-110 m/s）, with a temperature of 473 K at standard atmospheric pressure, were investigated. Results show that the MCPI generates much more arc discharge energy than the SI under a constant pressure; for example, the MCPI generated 6.93% and 16.05 % more arc discharge energy than that of the SI at 30 kPa and 50 kPa, respectively. Compared to the SI, the MCPI generates a larger area and height of plasma heating zone, and induces a much larger initial spark kernel. Furthermore, the lean ignition limit of the MCPI and SI decreases with an increase in the velocity of the inlet airflow, and the maximum velocity of inlet airflow where the SI and MCPI can achieve successful and reliable ignition is 88.7 m/s and 102.2 m/s, respectively. Therefore, the MCPI has the advantage of achieving successful ignition with high-speed inlet airflow and extends the average ignition speed boundary of the kerosene/air mixture by 15.2%.
文摘The utilization of graded Al powders offers the possibility to adjust the combustion performance of Al powders,while simultaneously safeguarding their energy properties.In this paper,a series of graded Al powder have been incorporated into the typical Al@AP composites through the spray drying technique.The thermal behavior,ignition and combustion characteristics were comprehensively evaluated and compared.The experimental results showed that with the varying inclusion of the graded Al,the heat of reaction exhibited a significant change,ranging from 9090 J·g^(-1) to 11036 J·g^(-1),which was strongly dependent on the particle size of Al.The combination of Al with diverse range of particle sizes in graded configuration serves to significantly enhance the decomposition of AP,resulting in the disappearance of the LTD stage and a conspicuous decrease of at least 11.7℃ in the peak temperature of the HTD.Furthermore,the maximum burning rate achieved by the Al-3@AP composite was 33.6 mm·s^(-1),which was exactly twice as high as that of the graded Al-1@AP composite with the lowest burning rate.Diffraction peaks corresponding to unburned Al were detected in the condensed combustion products of Al-1@AP,and the combustion images clearly indicated an incomplete combustion tendency for this sample.In contrast,a well-designed gradation of Al powders,such as a combination of fine Al powders with a particle size below 5μm,has proven to be the most conducive to enhancing the combustion efficiency of the composites.
文摘In this study,an artificial neural network(ANN)is developed to predict the performance of a spark-ignition engine using waste pomegranate ethanol blends.A series of experiments on a single-cylinder,four-stroke spark-ignition engine yielded the data needed for neural network training and validation.70 percent of the experimental data was used to train the network using the feed-forward back propagation(FFBP)algorithm.The developed network model’s performance was evaluated by contrasting its output with experimental results.Input parameters included engine speed,ethanol blends,and output parameters included indicated and brake power,thermal,volumetric,and mechanical efficiencies.Training and testing data had regression coefficients that were almost identical to one.The research revealed that the ANN model can be a better option for predicting engine performance with a higher level of accuracy.
