Rhgenerative Braking And Propulsion

In surface mines large trucks are used lo move both the overburden and product. Payloads of 100* 1()3 and 2(>0xl03kg (220 500 and 441 000 lb J are common. A prototype unit of 35 x 104 kg (771 750 lb, J pay load, the Terex Titan, has been constructed in Canada and larger units are contemplated. These giant machines are powered by 735 kW (1000 hp) locomotive diesel engines driving an electric generator which in turn supplies power to the propulsion motors in the rear wheels. Smaller trucks, from 35 x 10* to 85 x 103 kg (77 175 to 187 425 lb,„) capacity, have a conventional mechanical drive from the engine through a transmission system to the rear wheels.

An application for Stirling engines exists with these large mining trucks to provide regenerative braking and propulsion. The principle of the combined regenerative braking and propulsion unit is simple. Consider, for example, the cylinder arrangement for the Siemens double-acting engine shown in Fig. 16.5. When operating as an engine producing power the expansion spaces are located in the heated spaces at the upper end of the cylinder. The compression spaces are ai the cooled lower ends of the cylinder. The direction of heat flow is into the engine at high temperature and out of the engine at low temperature with the production of some work at the shaft. The expansion space of one cylinder is connected to the lower end of the succeeding cylinder through the heater, regenerator, and cooler.

Now let the connections between cylinders be switched at the cold end so that the upper end of one cylinder is connected to the lower end of the preceding rather than succeeding cylinder. This causes roles of the hot and cold spaces to be reversed and the engine will attempt to run in the reverse rotation direction. However, if sufficient power is applied lo the

Regenerator

Fio. 16.5. Cylinder arrangement tor Siemens double-acting Stirling engine (or regenerative braking and propulsion concept.

Pislon

Regenerator

Fio. 16.5. Cylinder arrangement tor Siemens double-acting Stirling engine (or regenerative braking and propulsion concept.

engine shaft to drive the engine in the original forward direction it will operate, not as a prime mover, but as a heat pump. With the switching of the cylinder connections the lower ends become the expansion space abstracting heat from the surroundings to the working fluid. Similarly the upper ends of the cylinder become the compression space and heat is rejected from the working fluid to the heater. Thus, by simply switching connections between adjacent cylinders, the engine can be converted from a prime mover using high temperature heat and producing power, to a heat pump which absorbs power and generates high temperature heat.

When this system is applied to a Stirling engine equipped with thermal-energy storage in a mine truck, it can absorb power during down-haul operation to retard or decelerate the loaded truck and. at the same time, store the thermal energy to drive the empty truck back from the load tipple to the mine site.

The regenerative braking propulsion system was conceived by the author in the course of consulting work in coal mines in Alberta and British Columbia. These are located in mountainous regions and long down-haul operations of loaded trucks are commonplace. The same system can of course be applied in railway locomotive engines and in highway vehicles and is particularly attractive in mountain or foothills areas where considerable downhill braking is necessary.

Preliminary studies for mining trucks have shown that for loaded down-haul operations the fuel savings exceed 50 per cent. Economies of this order with 735 kW (1000 hp) engines in large fleets operating continuously arc very significant indeed, Further savings are attained in reduced wear and tear on mechanical braking systems and in improved safety in operation.

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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