Gas Turbine for Heavies in Five Years?
Page 72
Page 77
If you've noticed an error in this article please click here to report it so we can fix it.
Austin Development of 250 b.h.p. Industrial Gas Turbine Represents Lower Limit Efficiency as Applicable to An Automotive-type Unit SHOWN for the first time at the Electrical Engineers Exhibition at Earls Court on March 21, the Austin 250 industrial gas turbine is regarded by the makers, The Austin Motor Co., Ltd., Longbridge, as an important step towards the development of an automotive type of power unit.
At a preview of the turbine earlier in the month, Dr. J. H. Weaving, chief gas turbine engineer, said that a power unit of 250 b.h.p. had been produced because this output represented the lower limit for efficient operation as applicable to automotive-type units.
The industrial turbine is a singleshaft unit without a heat exchanger, but experimental work is well advanced in the development of a twin-shaft type equipped with . an efficient heat exchanger which will be suitable for heavy vehicles. In Dr. Weaving's view, commercial vehicles fitted with gas turbines will be operating on fast trunking routes within five years, the extension of the motorways being a potentially important factor in their efficient application.
12 Years' Work
Introduction of the industrial turbine follows 12 years of intensive experimental work. This included the production of a 120 b.h.p. unit with a heat exchanger which was fitted in an Austin Sheerline car (registration number TUR 1) in 1954, the vehicle being used as a mobile test bed over a number of years. The industrial turbine has completed a 500-hr. endurance test under full load, and turbine blades have been successfully tested under simulated running conditions for periods up to 2,000 hr., the main objective being the evaluation of fixing methods applied to the blade roots, which are developed with the aid of photo-elastic equipment.
OR
During the preview, Dr. Weaving agreed with a member of the staff of The Commercial Motor that a gas turbine was particularly suitable for contractors' machines of the heavier type for off-the-road work. He emphasized that the torque characteristics of a unit, combined with the gearbox giving three ratios, would give a performance superior to that of an oil engine of comparable output used in conjunction with a 10-12-speed gearbox. Moreover, of special importance, stalling torque would be three times the normal' operating torque.
Cheaper It is relevant that the cost of an industrial turbine in its bare form is £2,500, whereas a typical oil engine developing -250 b.h.p. costs around £3,000. With the development of an efficient heat exchanger the automotive version of the turbine is expected to operate as economically as an oil engine in terms of fuel consumption when producing full power, and to offer reduced maintenance costs. The gas turbine is easy to start, it can produce full power within a few seconds of starting and it will maintain peak output continuously without loss of tune. This is mainly the outcome of obviating piston rings.
The absence of a cooling system and the relatively light-weight constructtional features (based on kinematic principles) of the unit give freedom from deterioration or damage over a long period of idleness. Other vehicle advantages will include an increase in payload, which is indicated by a weight comparison between the industrial turbine and a comparable compression-ignition unit. Whereas the power-to-weight ratio of an oil engine is around 10 lb. per b.h.p., the turbine weight of 900 lb. gives a ratio of 3.6 lb. per b.h.p.
Dimensions include a length of 5 ft. 3 in., a width of 3 ft. 5 in., and a height of 4 ft. 3 in. The unit will operate satisfactorily on a wide variety of fuels, including derv, gas Oil, paraffin, petrol and methane. Lubricating oil consumption is relatively low and the exhaust gas is free from carbon monoxide and other unburnt products of combustion.
The compressor is of the single-stage centrifugal type operating at a ratio of 3.5 to 1 and supplies air to a single combustion chamber, where it is mixed with finely atomized fuel. Following combustion the gas is expanded through a two-stage axial turbine and thence passes to the exhaust exit. If a heat exchanger is fitted, air from the compressor is directed through the exchanger before it enters the combustion chamber, the hot exhaust gas being employed as the heating medium.
Power is, transmitted from the compressor end of the rotor to a double helical type of gearbox which reduces the rotor speed of 29,000 r.p.m. to an output speed of 1,500 r.p.m. The rotor is carried on two bearings, one ball and one roller, which are lubricated by oil jet.
Fuel Supply Developed by Joseph Lucas, Ltd.. the combustion chamber is of the sideentry type and incorporates a flame tube of Nimonic 75 housed in an aluminized mild-steel outer casing. Fuel is supplied by a Simplex atomizer from a piston-type fuel pump incorporating a governor control.
A particular feature of importance i to reliability s the method used for cooling the turbine discs and blades. These are maintained at a much lower temperature than that of exhaust gas by means )f cooling air supplied by the corniressor. Automatic devices protect he unit from overspeeding, excessive as temperature and loss of lubricating Al pressure.
The compressor impeller and the eparate guide vanes are machined rom forgings of RR 58 high-tensile iluminium alloy and are shrunk onto
he steel shaft. Aerofoil vanes are ised for the diffuser, whilst the coinwessor casing is constructed of wellibbed aluminium castings. The tur
as fUrbine (Contd.)
bine blades and discs are of Nimonic 90 forgings, and the nozzles are precision cast in HR Crown Max.
One lubricating system feeds oil to the bearings and a second system is used for oil circulation to a cooler. This is normally cooled by water but may be cooled by air with the aid of a fan. Push-button starting is provided by a 24-v. system, the d.c. motor being mounted on the gearbox. Drive is transmitted through a sprag-type clutch.
Of importance to the development of an automotive turbine, experiments are being made with both cross-flow and contra-flow heat exchanger, advance brazing techniques being used for both types to cater for differential expansion.
It is not considered that the more compact rotary-type heat exchanger, as developed in America, could be satisfactorily applied at an economic cost because of sealing difficulties.
Referring to the future of the gas turbine for cars and light commercial vehicles during the preview, Dr. Weaving said that it was unlikely that a suitable power unit would be produced within 10 years, The 50-b.h.p. turbine was, however, a "technical possibility."