Diesel Engine Possibilities
Page 47
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A DEVICE to supercharge a diesel 1-1engine to a degree determined by the torque requirement of the vehicle, thus giving virtually constant-power characteristics, was referred to in a paper prepared for the Institution of Mechanical Engineers by Mr. J. G. Dawson, B.Sc.. M.1.Mech.E., and Mr. N. M. F. Vulliamy, M.A., A.M.I.Mech.E., engineering director and chief diesel engineer respectively of F. Perkins Ltd., Peterborough. This was one of the several types of compound engine referred to by the authors, who felt that the true requirement for a vehicle was constant power independent of speed down to engine idling, or, in other words, an engine with a continuous rise in torque from the value required at governed speed down to idling speed.
Whilst admitting that the gas turbine, which could give a torque ratio of 3 or 4 to 1, had advantages in this connection. the authors pointed out that some form of gearbox or automatic transmission would still be required, thereby accentuating an already bad price situation. Another solution was a reciprocating engine linked to a gas turbine, whilst the third alternative was the type of differential pressure charged engine already referred to, which is more closely allied to existing diesel engines and which was 'originally propounded in 1955 by Dr. Glamann.
Mr. Dawson and Mr. Vulliamy felt that the only major advance towards
obtaining more power from a given size of engine must come from some form or other of supercharging, but that under present conditions the lower economic limit for blowing was about 4 litres, or
100 b.h.p. naturally aspirated. Above this, application of supercharging became increasingly attractive, and more supercharged — particularly turbocharged — engines could be expected in the reasonably near future, though the authors stressed that the increased use of turbochargers would not halt the development of normally aspirated engines.
Referring to "V" engines, the authors did not think that the V-6 configuration was likely to replace either the in-line six in the smaller sizes or the V-8 in the larger b.h.p. ranges, disadvantages of the V-6 being its greater weight at the same stress level than the in-line six, the need for increased balance weights and heavier flywheel, greater cost, difficult outputtorque characteristics and big enginemounting problems.
Weight reduction was likely to form a big part of future developments, the obvious approach being to use aluminium alloys instead of cast iron for such components as cylinder blocks and cylinder heads, though expense was a big drawback. Alternatively, improved foundry techniques could allow cast-iron blocks to be produced with substantially thinner minimum thicknesses, resulting in weight savings of up to 20 per cent.