Development of Ecoboy-SCM81

100 W class Stirling Engine, Ecoboy-SCM81

Introduction

Background

Configration of Heat Exchanger System

Mechanical Parts

Piston Ring

Experimental Results

Next Step & Future View

Introduction

A small 100 W displacer type Stirling engine is being developed under a project of a JSME committee, RC127. The project consists of sixteen Japanese academic researchers of universities and governmental laboratories and eleven enterprise members related to the Stirling field. The engine has very unique features. Its expansion cylinder is heated by combustion gas or solar energy directly, and a simple cooling system rejects heat from the working fluid. A regenerator is built in the displacer piston with heating and cooling tubes in which the working fluid flows from/to outer tubes. The outer tubes for heating were located at the top of the expansion cylinder and the tubes for cooling are in the middle of the cylinder.

The target performance is a 100 W output with 20 % thermal efficiency at the operating conditions of 923 K expansion space temperature, 343 K compression space temperature, and 1000 rpm.

Background

Many investigations and developments of Stirling engines have been proceeded. The Stirling engines have been considered attractive due to their promising role in helping to recent energy and environmental problems. Indeed, the characteristics of the engines such as high thermal efficiency, selectional flexibility on high-temperature source, clean and controllable exhaust characteristics, low noise and vibration are more attractive than those of conventional engines. Especially, we should note that the engines can easily realize their clean exhaust gas systems by the continuous combustion, and availability of use of various heat sources including solar energy. Although, in order to apply these characteristics, heating and mechanical systems with high efficiency which should be combined with the higher-efficiency owning Stirling cycle, have to be developed.

In Japan, two national R&D projects tried to develop the high-performance Stirling engines. From 1976 until 1981 the development of a marine engine was pursued by three companies under grants from the Ministry of Transportation and the Japanese Shipbuilding Research Association (Fujita et al. 1982). A two piston type engine was constructed as a part of a future 590 kW class four-cylinder double acting engine. From 1982 to 1988 four-type high-performance Stirling engines applied to heat pump systems and a generator set were constructed by four companies with technical assistance of three national laboratories under New Energy Development Organization funding (Sakai et al. 1988). Two companies for sealing technique joined the project. All of the engines could surpass the assigned goals and proved that well-designed Stirling engines are able to obtain the above mentioned advantages. Besides the national projects, many companies and universities including Nihon University and Meiji University are trying to develop other splendid Stirling engines in Japan.

In order to collect and arrange both the knowledge and design methods on Stirling cycle machines, a committee called RC110, was operated in JSME (Japan Society of Mechanical Engineers) from 1992 to 1994. A draft of the arranged design manual by RC110 promised to guide Stirling developers to their success. In 1994, another JSME committee, RC127, was established to confirm the design methods and arrange the knowledge on Stirling application systems. This committee consists of twenty-three researchers of universities and governmental laboratories and fourteen enterprise members related to the Stirling field. As one of the project activities, a small 100 W displacer type Stirling engine is being developed using the design manual. Actually, it is helpful to confirm the design methods.

Another is a W-type piston ring as shown in next figures. The W-type piston ring was invented by N. Isshiki in 1979 who is one of the authors of this paper. The piston ring has W-type slots inside and outside. The prototype of the ring has five slots outside it and four slots inside it as left of the figure. When the ring is set on a piston, two W-type piston rings is set with different position of the slots and a small pin is fixed to prevent sliding as right of the figure. The ring system does not need the tension ring because the ring is pressed to the cylinder by the tension of the slots itself. The ring system expects high performance of the working fluid leakage because the ring does not have a cut end. The ring consists of a few parts and can be made in low cost.

The material of all explained piston rings are based Teflon except the tension ring. The tension ring is made of the stainless steel.

Experimental Results

Now, we are working to set up and adjust some measuring system. Following figure shows one of the sampling data in such process. It may be imperfect data.

Next Step & Future View

A small 100 W displacer type Stirling engine Ecoboy-SCM81 was designed and is being developed within the RC127 JSME committee. The engine was designed based on a design manual established by the RC110 JSME committee. The prototype engine has many unique components, such as heater, regenerator, cooler, piston ring and others.

The next step of the research will be to measure and analyze the performance of the engine and the components. It is also hoped to complete a useful design manual for Stirling machines at our final stage.

JSME RC127 Committee

"Ecoboy-SCM81 Design Working Group"