Evaluating the efficiency of a linear based alternator in a free piston engine confuguration

Abstract

Electrical power generation with minimal negative impact, such as low noise ratio, reduced air pollution and reduced carbon footprint on the environment yet producing high efficiency, has become a goal for numerous research institutes and industries. Therefore, more desirable concept to solve aforementioned problems should be identified and implemented. However, several authors in the field of power generation have identified Free-Piston-Engine-Linear-Generator (FPELG) as a possible solution, due to its advantages, such as high efficiency, minimized volume, fewer frictional losses and reduced carbon footprint, as well as its economic feasibility, as compared to rotatory generators with crankshaft mechanism.

Despite the advantages of FPELG over rotatory generators, shortcomings of its own were found, such as piston balancing, system combination (linear generator and free piston engine), and stator design, to trap maximum electromagnetism energy, as well allowing smooth piston motion during energy generation. This study investigates this optimal operational efficiency of a FPELG design and development as an alternative electrical energy generation.

The study objective was to evaluate the efficiency of a linear based alternator in a free piston engine linear configuration, with an added necessity to develop a test bench for obtaining the results. Secondly, with this test setup, data was generated scientifically and evaluated to concur that this setup is economical.

Two types of generators (combustion and linear) were designed and built in two platforms. Firstly, the FPELG was physically built and with the same component specifications a Matlab@/Simulink program was developed to test the efficiency, voltage, speed and current during the system operation.

Secondly, a combustion engine was developed in Matlab@/Simulink for evaluation of the system efficiency as compared to Free Piston Engine Linear Generators. Both engines were examined based on frictional losses to determine which generator is the utmost efficient, compared to the other. Evaluating the assumptions that a linear based alternator in a free piston engine is more efficient were conducted and it was observed that the linear generator is travels at ~2m/s for a cycle of ~ 0.03s.

The speed of the generator depended on the air pressure as well as the load carried by the translator. It was observed that the load mass was exceeding the translator mass and as a result the translator speed was reduced. This caused a bend in the translator and resulted in the translator colliding with the stator.

The magnetic flux depended on the translator speed. However, the Matlab@/Simulink showed that the desired output power was feasible with that speed of 2m/s. The physical model also showed that the voltage obtained for all scenarios tested was feasible to meet the expected output power of 7W.

The system efficiency evaluation was based on the frictional losses. The combustion engines results were based only on Matlab@/Simulink program. However, it is assumed that the results obtained from Matlab@/Simulink program will match the results of the built combustion engines, as is the case for the linear generator.

The combustion engine is seen to experience additional losses, as compared to the linear generator. The losses experienced on the linear generator are lower, due to the fact that FPELG`s have less mechanical wear as compared to the combustion engines.

This research provides a design approach for the alternator, which comprises of the specific measurements for stator design. However, the translator is used as the prime mover between the engine and the alternator. The physical model is then combined into a single unit. Next, the results are simulated and compared to the simulation results from Matlab@/ Simulink between the linear generator and combustion engines. The program parameters used for the engine design are relative to the physical model, to compare the results of the same parameters.