Rolls-Royce Adopt Turbo-charging : Six-cylindered Oiler Gives 300 b.h.p.
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TURBO-CHARGING has been I adopted by Rolls-Royce, Ltd., for oil engines, the company revealed this week.
Equipped with an exhaust turbocharger, the Rolls-Royce C6_FL sixcylindered oil engine has an automotive rating of 300 b.h.p. at 2,100 r.p.m: and develops a maximum torque of 840 lb.-ft. at 1,400 r.p.m. This compares with an output of 250 b.h.p. at 2,100 ep,rn. and a maximum torque of 710 lb.-ft, produced by the unit when fitted with the standard Roots-type blower, The advantage of the turbo-blown unit in terms of fuel consumption is in the region of II per cent. when the engine is developing maximum power
and about 8 per eent, at maximum torque. The optimum consumption of the Roots-blown engine is approximately 0.38 lb. per b.b,p.-hour. The unsupercharged version of the engine has an automotive rating of 200 b.h.p. at 2.100 r.p.m, and produces a torque of 547 lb.-ft. at 1,300 r.p.m.
Two Blown Engines A turbo-charged C6.FL unit was one of two engines fitted with exhaustdrive us blowers shown by Rolls-Royce, Derby, at an "at home" organized by the oil-engine division, which started on Monday and will continue until the end of the week.
Supercharged by a Rotol turboblower, the C8,FL-eight-Cylindered unit develops 350 b.h.p. at 2,100 r.p.m., which represents a gain of 17 b.h.p. compared with the rating of the Rootsblown engine at the same speed. Maximum torque is increased from 950 lb.-ft. at 1,300 r.p.m. to 980 lb.-ft. at 1.400 r.p.m.
The Rotol blower is made 'tinder licence to the AiReSearch Co. of California, who have produced units for experiment with intercooled automotive engines.
Development -work in America on applications of intercooling to roadvehicle engines, using air-to-air and water-to-air heat exchangers, has been promising.
The six-cylindered engine may later be equipped with a different type of blower with similar principal features, which include a centrifugal compressor, an inward-flow radial turbine and inboard bearings. Water cooling is not employed for the bearings. The maximum speed of the smaller unit is over 65,000 r.p.m. and the rated speed of the larger unit is 55,000 r.p.m.
Reduced Speed When an intercooler is fitted the C8.FL engine has the same power rating as the turbo-blown engioe of 350 b.h.p., • but this is produced at the reducedspeed of l.800 r.p.m. and the maximum torque is increased . to 1,070 lb.-ft. at 1,200 r.p.m. Moreovet, the specific fuel consumption is appreciably improved, the gain being about 6 per cent, at reduced boost pressures and around 2 per cent. at the maximum pressure. Another outstanding advantage is that the exhaust temperature is reduced from 700° C. to about 625° C.
An American design of turbo-charger has been adopted on account of the relatively high maximum exhaust temperature of the engines. The ability to operate reliably at this temperature arises mainly from the characteristics of the materials employed.
All aspects of 'blower maintenance are being closely considered by RollsRoyce. Operators will probably have to return units to the factory for reconditioning,' but the vehicle should cover a large mileage between replacements. In America a mileage of 100,090 is frequently exceeded.
No Disadvantage
Whilst the elimination of acceleration lag has not been possible, it is claimed that it is substantially reduced compared with that which is normally associated with turbo-bloWers. It should not represent . a practical disadvantage to road-vehicle users.
For some time, production of turbochargers will be on a limited scale.
Other displays of particular interest at the "at home" include the Rolls-Royce " hot-shift" forward-and-reverse gearbox, which is intended for use in heavyduty tractors to provide an easy change from forward to reverse, with a consequent reduction of driver fatigue. The gearbox essentially comprises a planetary gear controlled by two hydraulic ally operated wet-plate clutches. •