Diesel Engine Troubleshooting

Archive for the ‘Uniflow Scavenge’ tag

Uniflow Scavenge Opposed Piston Diesel Engines

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In engines of this type admission of air is effected by ‘air piston’ controlled inlet ports, and rejection of products of combustion by ‘exhaust piston’ controlled exhaust ports. The motion of the two sets of pistons is controlled by either two crankshafts connected through gearing, or by a single crankshaft with the ‘top’ bank of pistons transmitting their motion to the single crankshaft through a crosshead-siderod mechanism. By suitable offsetting of the cranks controlling the air and exhaust pistons asymmetrical timing can be achieved.

It is evident that this system displays the same favourable characteristics as the exhaust valve in head system, but at the expense of even greater mechanical complications. Its outstanding advantage is the high specific output per cylinder associated with two pistons. However, the system is now retained only in large low speed marine, and smaller medium speed stationary and marine engines. In high speed form it is still employed for naval purposes such as in some fast patrol vessels and mine searchers, although its use in road vehicles and locomotives is discontinued.

Written by Ed

October 18th, 2011 at 3:12 am

Uniflow Scavenge Single Piston Diesel Engines

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In engines of this type admission of air to the cylinder is usually effected by piston controlled ports while the products of combustion are exhausted through a camshaft operated exhaust valve. Such systems are preferable from the standpoint of scavenging in that the ‘uniflow’ motion of the air from the inlet ports upwards through the cylinder tends to lead to physical displacement of, rather than mixing with, the products of combustion thus giving improved charge purity at the end of the scavenging process. At the same time it is now possible to adopt asymmetrical timing of the exhaust and inlet processes relative to bottom dead centre (BDC) so that, with exhaust closure preceding inlet closure the danger of escape of fresh charge into the exhaust manifold present in the loop scavenge system is completely eliminated. This system has been adopted in a number of stationary and marine two-stroke engines.

Written by Ed

October 18th, 2011 at 3:10 am

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