• Direct-injection Adopted for
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New Thornycroft Oil Engines
New Form of Combusilon ChambeI Employed on Company's Latest Products
ANimportant change in the design of the oil engines produced by John I. Thornycroft and Co., Ltd., Thornycroft House, London, S.W.1, for its road vehicles 'concerns the introduction of heads of the direct-injection type. Hitherto, separate combustion chambers have been used, swirl being promoted under the influence of the
compression. In the present design, swirl in the . combustion chamber is promoted during the induction phase of the cycle. The air ports are shaped so as to give the incoming air a rapid swirling motion without the .need • for employing masked inlet 'valves.
The atontizers are disposed centrally between the valves, on the bore centre line. Injection from the pump, which is of C.A.V. manufacture, is through a multi-hole sprayer, the injector spring setting causing fuel admission to commence when a pressure of 2,560 lb. per sq. in. is reached. The compression ratio adopted is 16 to 1. In both the four-cylindered and six. cylindered models the bore and stroke
dimensions are respectively ins. and 6 ins., the smaller engine having a capacity of 5.25 litres and the larger Unit 7.88 litres. At 1,600 r.p.m. the rating of the former is 60 b.h.p., with a maximum torque of 223 ft.-lb.,. whilst the b.m.e.p. is 105 lb per sq. in at 1,000 r.p.m, The governed speed is 1,600 r.p.m., and the piston speed 1,600 ft. per minute.
In the case of the six-cylindered engine the rating, at 1,800 r.p.m., is 99 b.h.p., with a maximum torque of 342 ft.-lb., and a b.m.c.p. of 107 lb.
per sq. in. at 1,000 r.p.m. At the governed speed of 1,800 r.p.m.,. the piston speed is 1,800 ft, per minute.
Apart from the change in the combustion system, the rest of the engines remain substantially as before. Monobloc castings are used for the crankcase water-jacket units, the casting, in each case, being extended well below the main bearings to provide for the maximum rigidity. The distribution drive is at the forward end and as these engines are intended for installation in
forward-control chassis all the auxiliaries, with the • exception bf the starter, are mounted on the near side. •
As the accompanying illustrations show, the air exhauster and injection pump are driven in tandem, whilst the water-circulating pump and dynamo are driven by a common shaft.
Forced circulation is adopted throughout the cooling system, in which .particular attention has been paid to the proportions of the waterjacket at the cylinder head. A V-belt drives the fan from a pulley mounted on the forward extension of the camshaft.
In the four-cylindered engine, five white-metalled bearings are employed to carry the balanced crankshaft, whilst in the case of the larger unit seven bearings are used.
The upper halves of the big-end bearings are lined with lead bronze. and the caps with white metal, all being steel backed. With the exception of the pistons 4nd gudgeon pins, which depend on splash and oil mist, pressure lubrication applies throughout.
Wet-type cylinder liners, individually replaceable, are adopted. The smaller model weighs 1,296 lb., and the larger 1,680 lb., figures which give a power. weight ratio of 2q lb. and 17 lb. respectively per maximum .b.h.p.