There are limited studies on improving the piston expander performance for a wider operating range by adopting the variable valve timing method. This study uses a simple conversion technique to develop a single-piston expander (SPE) from a small two-stroke engine. The SPE is being tested at different operating conditions to study the feasibility of the SPE operating under different intake pressure and valve timing conditions. By fixing the exhaust valve timing, the SPE was tested at four intake pressure; 3, 4, 5, and 6 bar, while the intake valve closing varied from 30° to 110°. From the study, the highest power produced by the SPE was only 64 Watt when tested at 6 bar, with the intake valve opening at TDC and closed at 70°. The results show that the converted SPE is feasible in terms of functionality, but it is not performance-wise because much power has been lost through the recompression process. The study also observed that the intake valve timing could significantly affect the SPE power output, besides the intake pressure alone.
An electronic valve timing control unit has been developed mainly for the internal combustion engine operation. This study aims to implement a similar technology into a single-piston expander (SPE) with readily available and low-cost microcontrollers. The study used an Arduino Mega 2560 and ESP32-WROOM microcontrollers to control the valve timing with the rotational input signal obtained from an absolute encoder. The SPE has been expected to run at the rotational speed of up to 2000 rpm. This setup was prepared to simulate the actual SPE operation using a direct current motor to drive the spindle connected to the encoder shaft to create a similar hardware testing and controlled environment. The study aims to identify the efficiency of the microcontroller’s performance with a variation of the valve’s opening and closing time. Results have shown that the clock rate of the microcontroller affects the performance of valve timing response. By increasing the clock rate, the microcontroller can control the valve at a higher speed.
Abstract. This paper presents the progress of a small-scale dynamometer prototype development for performance measurement of a reciprocating piston expander (RPE). Since the available dynamometer systems in the market are limited to specific applications that require for the customization, their price normally very expensive. Since the current study on the RPE required a dynamometer unit, therefore, a new and cheaper dynamometer prototype that was suitable for RPE application has been developed. Using air as RPE working fluid, a case study has been carried out to measure its performance at different inlet fluid conditions, i.e., within 20℃−140℃ and 3−5 bars. The results observed that the performance of RPE was proportionally increased to the increased of inlet fluid pressure and temperature. The maximum brake power produced was 27 Watt when the RPE operated at 140℃, 5 bars and the speed of 820 rpm. It also revealed that the changes in the pressure of inlet fluid can give significant change on the performance of the RPE due to its direct relation to the RPE actual rotating force. Although the RPE and dynamometer seem good being adapted to each other, both of them require some improvements to ensure both systems well operated and reliable.
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