Tempiuature Control Systems

The temperature control systems used in Stirling engines are all basically similar. The principle is that the temperature of the heater tubes (or other critical part) is to be maintained constant at all operating condi-

lions. The temperature is monitored by a thermocouple which generates a signal for some control device regulating the air flow, fuel Mow or both to maintain the temperature constant.

The essential features of the United Stirling temperature control system ¡ire shown in Fig. 10.3. Hallare and Rosenqvist (1977) describe the air fuel control systems as follows:

'The temperature of the heater tube is measured by a thermocouple 1. I'lic signal nf the thermocouple is amplified and converted in the electronic control unit 2 to a signal controlling the posiiion of the air throttle 3. Thus the right amount of air is delivered to the combustor via the burner air Idowcr I. to a slightly modified Bosch k-Jelronic unit, a sensor plate 6 installed inside a conical air passage provides a posiiion indication of air flow rate.

'Hie fuel Irotn lite tank 5 passes an electric pump 7 and a filter 8. The fuel pressure is held constant by a relief valve 9. The position of the sensor plate controls, via a plunger III. the amount by which a fuel metering port is opened.

The dilferentinl pressure across the metering port is maintained at a constant value by a valve 11 so that the fuel flow it» the atomizer depends only upon the amount the port is opened.

The air-fuel ratio depends upon lite hydraulic counter pressure controlled by a pressure regulating valve 12. Adjustment of the ratio over the load range can be achieved by a modification of the shape of the conical air passage'.

6 Sensor plate

7 Fuel pump »osch K Jetronic Unit X Filter

9 Relief valve

10 Plunger

11 Differential pressute valve 1?. Pressure regulating valve

FlG. 10.3. Schematic diagram of United Stirling fuel/air control system (after Hallare und

Rosenqvist 1977).

Fuel control

Fuel control

Flo. IDA Schematic diagram of Philips/Ford Inel/air control svstem (after Postma ef af.

Flo. IDA Schematic diagram of Philips/Ford Inel/air control svstem (after Postma ef af.

A system essentially similar was described briefly by Postma et al. (1973) for the Philips/Ford Type D.A. 4-215 engine. The system is shown schematically in l:ig. 1.0.4 and was described by Postma as follows:

'The Stirling engine fuel control is designed so that the engine heater tubes arc operated at n constant temperature of 1470®F (799 °C). A temperature sensor mounted on one of the heater tubes' is the primary control devicc in the air and fuel control circuit. The combustion blower is driven directly from the engine. The amount of air supplied is regulated by the temperature sensor through a throttle valve which is interconnected with (he fuel/air control to maintain a constant A/F ratio (30 per cent excess air)'.

Earlier Ncelcn et al. (1971) briefly described the fuel control system used on the four-cylinder rhombic-drive Philips I'ype 4-235 traction motor developed for installation in buses.

No description ol the fuel/air control system used on MAN/MWM engines was found in any of the references consulted but it is thought to be similar to those discussed above.

Solar Stirling Engine Basics Explained

Solar Stirling Engine Basics Explained

The solar Stirling engine is progressively becoming a viable alternative to solar panels for its higher efficiency. Stirling engines might be the best way to harvest the power provided by the sun. This is an easy-to-understand explanation of how Stirling engines work, the different types, and why they are more efficient than steam engines.

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