Analysis of Stirling engine

Japanese

The purpose of Analysis

The Stirling engine has many features that is a low pollution and can use low temperature, but it has never put to practical use. Because the Stirling engine is low power compared with gas engines. Especially low temperature Stirling engine, it is circumscribed the low heat value within its size. If we want to take out more power, we must decrease many losses. So, analysis is important because Stirling engine seal up gas, of Stirling engine is accurately. If we corrects analysis data of Stirling engines, we will be able to know the relation between the power and losses of various kind, and we can take out much power and high efficiency.

The analysis of Stirling engine are parted on three methods.

1st-order method
The analysis is use of experimental value and engine size, or use the ideal analysis models. For example Beal Number and schmidt model and ideal adiabatic model.

2nd-order method
The analysis take into consideration losses of various of kind. Theses use the result of ideal analysis and analysis losses of various kind. For example isothermal model and adiabatic model.

3rd-order methods
The analysis solve homogeneous equations of flow and equations of kinds losses. The analysis solve relation between losses. For example quasi-steady flow model.

We explane some of analysis for Stirling engine.

1. Beal Number
Beal Number is experimental number for estimate shaft power. The Stirling engine's shaft power is affected by engine pressure, power piston volume and engine speed. So, Beal Number is shaft power per the three elements. Beal Number has been publication for high temperature engines, but never been publication for low temperature engines. So, we research for wide aria Beal Number.

2. Isothermal model
We part engine elements to five elements, expansion space, heater regenerator, cooler and compression space. Isothermal model assume that gas temperature in elements are isothermal for cycle, and this model called schmidt model. This analysis model is most famous for analysis of stirling engine. There is analysis equation for this model.

3. Adiabatic model
Adiabatic model assume that gas temperature in heat exchangers is isothermal, but expansion gas and compression gas is adiabatic. Heat exchange is done in heat exchangers, so Adiabatic model is akin to real engine than isothermal model.

4. Quasi-steady flow model
Quasi-steady flow model solve homogeneous equations of flow and losses of various kind. Engine elements part to more pieces as the need arias. Old Quasi steady flow model use temperature of heat exchanger's wall, but our Quasi-steady flow model solve by heat source temperature, and we can know drop of heat source temperature, too.

The Stirling engine has many losses and we explane some losses.

1. The flow loss
The stirling engine has three heat exchangers, and the pass of gas in heat exchangers is very narrow. Especially regenerator has much opposition and it is amount to 90 percent of total flow loss. The flow loss is one of large loss of all stirling engine losses.

2. The gas leakage
Because of stirling engine must seal up gas, the gas leakage much effects to power.

3. The heat transfer loss
When the heat escape on the engine wall and heating surface, the heat does not change the work. Especially a big size engine or a high temperature difference Stirling engine has large effect.

4. Regenerator loss
The regenerator is a kind of heat exchangers to save an excess heat. If the regenerator efficiency is 1, the engine heat efficiency is equal Carnot efficiency. But the regenerator exchange much heat its loss has large effect for power. But increased regenerator matrix is cause of much flow loss. So, the relation is impossible.

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