Here's some stuff on the incredible Nomad engine. I found a snippet of text from LJK Setright's book which I have included in this post. The first time I saw this cutaway illustration in a book from the local library, I'm pretty sure my jaw literally dropped.
From 'Some Unusual Engines', LJK Setright, ISBN 0852982089
>
>
> On the other hand, a far more thorough (if not to say brilliant)
> exploitation of compounding principles by Napier enjoyed no
> success at all: their Nomad engine, conceived at a time when
> propellors were expected to be the normal means of airliner
> propulsion, did not mature until the aviation world had gone over to
> jets. Like so many unusual engines, it arrived too late ; and to be
> truthful it may be argued that it never really matured anyway, since
> it was by all accounts a pig to start.
>
> Looking at its specification, this hardly seems surprising. The
> Nomad was a 12 cylinder horizontally-opposed liqid cooled two-
> stroke compression-ignition engine cmpounded with an exhaust
> gas turbine, both of these units driving a single propellor shaft
> through reduction gears. Even the basic construction was
> satisfying: the crankcase was a two-piece structure of magnesium
> alloy castings, the two cylinder blocks were of aluminium alloy with
> dry liners fitted in each cylinder bore. Each of the cylinders had its
> own aluminium cylinder head, elegant and simple in shape
> because the 8 inlet and three exhaust ports of each cylinder were
> of course in the walls.
>
> As appropriate to a 2-stroke the the ratio of bore to stroke was
> unfashionably low, resulting in measurements of 6 and 7.375
> inches respectively. This yielded a displacement of 2505 cubic
> inches, (41.2 litres), making a fairly big engine thet weighed
> 3580lb. Beneath and behind the crankcase was the turbine
> department, where a three-stage axial flow turbine rotor was
> mounted on a shaft which drove through a variable-ratio Bair fluid
> coupling and gearing which connected it to the propellor shaft -
> which in turn conected through reduction gears to the crankshaft.
> Coupled ot the turbine shaft was the compressor, a twelve stage
> axial flow affair delivering air to the cylinders at very high pressure
> (8.25 atmospheres) and in enormous quantities (13 lb/sec at
> maximum speed)
>
> Many an engine of much less complication has been debased by
> some want of efficiency in one of more of its component elements.
> It is a tribute to the design of the Nomad that,
> with so many constituent sections that could
> have let it down , it was in fact of
> extraordinary efficiency. The whole operating
> cycle was designed to extract every possible
> quantum of energy: nothing was allowed to to be
> wasted at any stage. After combustion was
> initiated by the injection of diesel fuel into
> the cylinders, the initial expansion of the charge would deliver
> power through the pistons to the crankshaft. As soon as the
> exhaust ports were uncovered expansion would continue through
> the exhaust manifold to the turbine, where the gasses and residual
> hot air produced by combustion would liberate more power for
> transmission through the hydraulic coupling to the propellor shaft.
> The total power from the crankshaft and turbine was considerable,
> and with water injection the take-off rating was 3476hp at 2050
> rev/min. But there was more to come: there as still a little energy
> left in the exhaust gasses even after negotiating the turbine, and
> this was squirted out as a jet at the back to produce a further
> 250lbs of thrust, maing a total equivalent horspower of 3570.
>
> This was equivalent to a BMEP of 205 psi, a very high figure for a 2-
> stroke. The other specific performance factors were no less
> impressive: the engine weighed virtually one pound per horsepower
> and developed 10.5 hp for every square inch of piston area - which
> provides a revealing comparison with the 6.58 hp.in^2 of the Wright
> Turbo Compound. At maximum continuous rating the Nomad
> developed 2248 equivalent horsepower, ; but looming overall was an
> incomparably mean specific fuel consumption. The engine had after
> all been concieved as the propulsive unit for a really long range
> aircraft, intended to realise the most outstanding economy. Napier
> claimed 0.33 lb/hp.hour, although Air Vice Marshal Banks has
> hinted that it never quite achieved that.
>
> It was nevertheless a most satisfying performance. Napier were not
> to be satisfied though, for thay argued that it ought to be possible
> to do something with the unburned air in the exhaust system. A
> diesel can only burn 70% of the air it breathes: they therefore
> inserted an afterburner nozzle in the exhaust manifold, injecting
> extra fuel to burn the remaining oxygen and thus allow the the
> turbine to make a much greater contribution to engine output.
>
> This and an intercooler betwen the the compressor and the
> cylinders added a mere 170lb to the total weight of the engine; but
> the result of this slight investment was a fantastic profit of no less
> than 530hp. On this basis the specific weight fell to 0.83 lb/hp -
> and who would have though that any diesel would have proved to be
> relatively lighter than the majority of spark-ignition engines gulping
> relatively larger quantitis of the best quality petrol?
Here's a better cutaway of the Sabre H-24
[This message has been edited by desmo (edited 04-15-2000).]
