Big-engine Performance: Small-engine Economy
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Ivy using a B.S.A. 100-200 turboLi charger. the output of a Daimler 8.6-litre engine fitted in a Daimler CVD.6 double-decker has been raised to match the performance of the 10.6-litre unit of the Daimler CVD.650 double-decker,
As reported on page 34, the 8.6-litre unit has been tested by Halifax Passenger Transport Department, and a 10.6-litre engine was employed on similar experimental runs to provide comparative data.
Halifax was chosen for the tests on account of the steep gradients included in many of the routes. The trials were not, however, intended to demonstrate the maximum gain that could be derived from turbochargers. The blower was operating well below its maximum boost pressure.
5-6 per cent. Saving On the hilly routes. with many stops and on non-stop runs with steep inclines alternating with level sections, the fuel-consumption rate of the CVD.6 double-decker showed a saving of 5-6 per cent., compared with the fuel used by the CVD-650. despite a finaldrive ratio that was below the optimum' for the engine output.
Although the test-bed output of the blown engine was generally similar to the rated performance of the larger engine, the acceleration of the CVD.6 showed to advantage throughout the normal speed range. The vehicles were loaded togive the same gross laden weight.
On a level run with many stops the blown engine had a slightly higher consumption than the 10.6-litre unit, and this is attributed to faulty matching at idling speeds. B.S.A. technicians are coolident that correct matching will give an improved consumption under these conditions and that modifications to the injection system will enable further gains to be obtained throughout the range.
No Lag in Acceleration It is claimed, that the test bus accelerated with complete absence of the momentary initial lag normally associated with turboblowers. Laboratory tests observed by a representative of The Commercial Motor confirmed that the lag, if any, was negligible.
Test-bed results show that the maximum fuel saving so far obtained by turhochareing the 8.6-litre engine, compared with the consumption of the 10.6-litre unit, is about 8 per cent., the respective rates being 0.345 lb. per b.h.p.-hr. and 0.375 lb. per b.h.p.-hr. Tests in the laboratory and on the track have proved that engine noise is reduced by turbocharging.
According to the performance curves, the blown engine develops a slightly a6
greater power than the larger unit between 1,200 r.p.m. and 1,500 r.p.m., whilst its maximum output of 137 b.h.p. at 1,800 r.p.m. is about 6 b.h.p. below that of the 10,6-litre engine. In normally aspirated form the 8.6-litre engine develops 124 b.h.p. at lo800 r.p.m.
In the case of a 9.6-litre engine of another make, the blower has been used in combination with an air-to-water intercooIer to raise the normal output from 140 blot). at 2,000 r.p.m. to 222 b.h.p, at the same speed and the maximum b.m.e.p. from about 105 p.s.i. to 180 p.s.i. at 1,350 r.p.m. B.S.A. engineers envisage the use of air-to-air intercoolers for vehicle applications as a probable development.
Down-rated for Economy During the dynamometer tests of the 9.6-litre supercharged engine its power was reduced by adjustment of the rack setting to the normally aspirated rating, and in this case the turboblower afforded a maximum fuel saving of 121 per cent., whilst the average saving from 1,400 r.p.m. to the maximum of 2,000 r.p.m. was more than 10 per cent.
This indicates the potential economy of a blown intercooled engine with a normal rating, which would be combined with a facility to increase the output to compensate for wear or altitude variations. An engine could be equipped with an automatic boost control to compensate for altitode changes.
1,01110-bethr Overspeed Test Both the turbine and compressor of the B.S.A. unit are of the radial-flow type, and the blower operates at 'a Compression ratio of 11 to 1 at 45,000 r.p.m. and 2 to I at 59,000 r.p.m. The reliability of the unit has been demonstrated by a 1,000-hour overspees.1 test at 66,000 r.p.m. and a turbine temperatture of 650° C. It is claimed that the condition of the parts at the end of the run indicated that the blower could have operated satisfactorily for a much longer period, the loss of efficiency being only 21 per cent. Further tests are bhng made without reConditioning the parts.