Turbo-charging background

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Turbo-charging background

I was interested to read Mr. Winstanley’s tette’ in October MOTOR SPORT, especially as he mentions the Napier Nomad as an example ol technical ingenuity. Unfortunately, his description of the engine as an opposed piston two stroke in triangular form is not correct, this engine was in fact known as the Deltic and was a marine / industrial unit.

The Nomad aero engine was a flat 12 cylinder compression ignition two stroke compounded to a 12 stage axial compressor, driven by a three stage axial turbine. Excess power from the turbine was fed through a Beier variable speed hydraulic gearbox to the propeller shaft, which was also driven through a reduction gear by the piston hall of the engine. Finally, there was still some residual energy left in the exhaust gases and this was used as jet thrust. This highly technical and complex unit is very well detailed in L. J. K. Setright’s book “Power to Fly”.

The Deltic was a high speed opposed piston two stroke compression ignition unit with the cylinders arranged in three banks to form, in section, an inverted equilateral triangle with a crankshaft at each corner. The basic engine was developed in 18 and nine cylinder form with a gear driven two sided centrifugal scavenging blower. Alternatively the engine could be fitted with a turbo-charger or compounded by the addition of axial flow compressor / turbine unit located within the triangular space between the cylinders.

The Deltic was originally developed as a lightweight high-speed, high-output marine engine for naval use. The high-output series being scheduled for fast patrol boats of the “Dark Aggressor” class and similar craft for other navies. The lower power or “commercial rating’. engines being destined for minesweepers, where engine low magnetic content was advantageous.

As an alternative to the marine engine, The English Electric Company built locomotives for British Rail using two commercially rated 18 cylinder units. These engines were also used to power mobile generators, compressors audio one case a refrigeration unit.

The capacity of the 18 cylinder unit was 86.9 litres and power outputs ranged from 1,700 to 2,500 h.p. depending on engine standard and 3,850 h.p. for the compound unit at engine speed of 1,500 to 2,000 r.p.m. In addition to the two types of engines, Napier built a series of turbo-blowers for fining to large diesel engines. Throughout the period of dcsign and development of these engines, H. Sammons and later E. Chatterton were Napier chief engineers, and I doubt that Major Halford was at all concerned, as by this time he was involved with Rolls-Royce.

I hope this letter will be of interest and will clear up a, confusion about the two engines. CLIFFORD ENGLAND Great Barbed, Bedford