D

Figure 28.28 General Motors EMD 710G two-stroke medium speed engine with overhead camshafts and unit injectors

Figure 28.29 Cross-section throiÁgh Bolnes VDNL 150/600 two-stroke engine

an output band from 400 kW to 2800 kW. The crosshead took the form of a lower piston/scavenge pump, with uniflow scavenging arranged via a single valve in the head. Air is drawn in by the turbocharger, passes through a first-stage air cooler to the scavenge pump and then fed to the cylinder for the compression stroke via a second-stage air cooler.

Bolnes cited the following merits of the design:

• Very low lubricating oil consumption due to the complete separation of combustion space and crankcase.

• Unique air control due to the design of the 260 mm bore crosshead scavenge pump which was claimed to secure completely smokeless combustion under all load conditions.

• High performance at low speed (for example, 110 per cent torque at 70 per cent rev/min).

• Separate lubrication systems promoting good heavy fuel-burning operation.

• Simple maintenance.

Bolnes engines had a faithful following in fishing, dredger, coaster and survey vessel propulsion sectors. The design was also valued as a test engine in fuel and lubricating oil research laboratories.

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