Maximum Power at 8,000 ft.
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pOWERED by a D.A.F.-Leyland 0.350 turbocharged engine, an irticulated tandem-axle trailer outfit was recently tested on the GrossgIockier Pass in Austria by technicians of Ltd., Turbocharger Division, Warple ,Way, London, W.3, to assess the effect of altitude changes on the mgine's output, torque characteristics, !uel consumption and so on. Built by Van Doornes Automobielfabriek N.V. A Eindhoven, Holland, the vehicle had t gross weight• of 181 tons and turbo;harging increased the sea-level rating A the engine from 100 b.h.p. at 2,200 -.p.m. to 140 b.h.p. at 2,400 r.p.m. Tests were made from an altitude of ,000 ft. up to 7,800 ft. on a gradient tarying between 12 per cent, and 14 )er cent., and demonstrated that turbo;harging can enable maximum power o be maintained up to 8,000 ft. The )utput of a naturally aspirated engine Nould have been reduced by 26 per rent. to 74 b.h.p., and the gain in per
formance that can be attributed to turbocharging is, therefore, over 89 per cent.
Test results also show that turbocharger speed is increased by 1.83 per cent. per 1,000 ft. and that some power is lost at lower engine speeds. According to C.A.V., the makers of the turbocharger, this increase in turbocharger speed is acceptable up to 10,000 ft., and it has been estimated that loss of maximum power over about 8,000 ft. would be 2.1 per cent, per 1,000 ft. This is qualified, however, by the observation that the percentage loss at higher altitudes is reduced when the boost pressure at sea-level is increased.
Torque readings taken during the tests show that the sea-level torque rating of 255 lb.-ft. at 1,400 r.p.m., is raised to 340 lb.-ft. at the same speed, and that at 6,500 ft. the torque is reduced to about 300 lb.-ft. Taken over a number of tests, measurements of fuel consumption indicate that specific fuel consumption tends to incr ase slightly with altitude, but that the increase is negligible between 4,00 ft. to 7,500 ft.
It is notable that there was yin ally no variation in exhaust gas tern rature with changes of altitude, w ich contrasts with the observations ade by some engine makers on the e ects of altitude. Inlet and exhaust press res were constant throughout the test Amongst other interesting co lusions that can be drawn from the t sts, it is apparent that the availabilit of optimum gear ratios is more impo ant than the shape of the engine to que curve. When the driver of the ye icle had to change down from second ear to first gear with an increase in gra lent from 12 per cent. to 14 per cent., en ine output was reduced to approxim tely 80 b.h.p., which left a surplus o 60 b.h.p. which could not be used bee use no suitable intermediate gear wag available,
Improved 96 per cent.
Laboratory tests in an Easterniloc country have been conducted to sir dy the effects of altitude up to I 8,001 ft. on a turbocharged engine, the nit being designed to give a zero gai at sea-level and maximum advantag at 20,000 ft. The engine used for ti ese tests developed 100 b.h.p. at sea-1 vet and over 93 b.h.p. at 18,000 ft.. whe eas the output of a naturally aspirated ersion of the unit would be reduce to 48 b.h.p. The improvement in ou put provided by turbocharging was, t fore, about about 96 per cent.
Comparison between the specific vet consumption of naturally aspirated and turbocharged engines shows tha at 16,000 ft., consumption is increase by some 5 per cent. and 120 per c nt. respectively. At 8,000 ft. the consu ption increase is less than 2 per cent, for the turbocharged engine, whilst the consumption of the naturally aspir ted engine is increased by 36 per cent