The free piston linear expander (FPLE) is an energy conversion device that converts mechanical energy into electric energy by using a linear electric machine (LEM) without emission. This research addresses the numerical modeling of a dual-piston air-driven FPLE constructed on the basis of the free piston engine linear generator (FPELG) concept. The model was built in MATLAB/Simulink. The simulation results were in good agreement with the experimental data. Where the in-cylinder pressure and displacement profiles attained errors of less than 10% (within the acceptable range). Then, the predicted results of the simulation model, namely, the displacement profile, in-cylinder pressure, piston velocity, and engine power results were analyzed. Findings indicate that intake pressure was the most important parameter for enhancing engine performance. The in-cylinder pressure increased by approximately 16% and 21.7% when the intake pressure was increased from 5 to 6 bar and from 6 to 7 bar, respectively. The piston velocity increased by approximately 12.3% when the intake pressure increased by 1 bar. Finally, engine power increased by approximately 26.5% and 30.6% when the intake pressure increased from 5 to 6 bar and from 6 to 7 bar, respectively.

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The methodology used to establish the air-driven expander FPE is discussed in this section. Here, the FPELG operation concept may be described as the forces used in the FPLE. The forces are classified into four parts, namely, the force acting on the right piston, the force acting on the left piston, the force of LEM, and the total friction force. Assuming the compressed air is provided to the left chamber then the piston is moved from TDC to BDC. During this movement, the energy is stored in the right chamber. Then, the pressure in the right cylinder pushes back the piston again to the left side. By repeating this process, a resonance movement is generated, and the current is generated by the LEM. In this study, MATLAB/Simulink was used on the basis of a zero-dimensional model to build the FPLE system's model. According to mathematical equations, the model should include the forces that originate from the left and right cylinders (i.e., the air-driven expander), the LEM force, and the friction force. Figure 6 shows the simulation model of the air-driven FPLE built using MATLAB/Simulink. Some assumptions are considered in this model. The parameters such as gas leakage and heat transfer are neglected because of their extremely small values. Based on Newton's second law, the dynamic model is built as shown in Figure 6. It can be seen from the figure the left and right cylinder models are connected to the LEM model. In addition, the system model, including the friction sub-model and control, is developed. Figure 7 shows a detailed dynamic model of the FPLE simulation. While Figure 8 shows a detailed simulation model of the air-driven expander for a cylinder of the engine side, which is similar to the configuration in the other side. Figures 9 shows the LEM model. The simulation model is validated using experimental data. By using this model, the characteristics of the air-driven expander FPLE, such as the piston linear position profile, velocity of the piston, the in-cylinder pressure, and the engine power can be investigated.

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This study established a numerical model of the dual-piston air-driven FPLE based on the FPELG concept. MATLAB/Simulink was used to build the zero-dimensional numerical model. Experimental data were used to validate the simulation results. The simulation results were in good agreement with experimental data for both in-cylinder pressure and displacement profile. In addition, the measured error was within the acceptable range of less than 10%, indicating that the model can successfully predict the results. The effect of intake pressure on displacement profile, in-cylinder pressure, piston velocity, and engine power were also investigated in this study. The simulation results also showed that intake pressure plays a significant role in FPLE engine performance. The in-cylinder pressure was increased by approximately 16% when the intake pressure increased from 5 to 6 bar. While the in-cylinder pressure was increased by approximately 21.7% when the intake pressure increased from 6 to 7 bar. As for piston velocity, a linear relationship was observed between intake pressure and piston velocity, and the increase was approximately 12.3% when the intake pressure was increased by 1 bar. Moreover, engine power was increased by approximately 26.5% when the intake pressure was increased from 5 to 6 bar. While the engine power was increased by approximately 30.6% when the intake pressure was increased from 6 to 7 bar. This study has presented a fundamental analysis of FPLE engines. Further research is required to explore in detail the optimal value of intake pressure.

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Technology Description:The FPLE is an energy conversion device utilizing a linear electric machine (LEM) to convert mechanical energy into electric energy.

Research and Development:The research focuses on numerical modeling of a dual-piston air-driven FPLE based on the free piston engine linear generator (FPELG) concept.MATLAB/Simulink is used for building the simulation model, and the results show good agreement with experimental data.

Performance Analysis:The simulation model analyzes various parameters, including displacement profile, in-cylinder pressure, piston velocity, and engine power results. Findings highlight the significance of intake pressure in enhancing engine performance, with specific percentage increases noted.

Market Potential Indicators:The technology's ability to convert mechanical energy into electric energy with low emissions aligns with the growing interest in sustainable and environmentally friendly energy solutions.The positive correlation between intake pressure and engine performance could attract attention from industries seeking efficient energy conversion solutions.

Performance Improvements:The noted improvements in in-cylinder pressure, piston velocity, and engine power with increased intake pressure indicate potential for optimization and application in various contexts.

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