Mirrlees Blackstone

An impressive medium speed enginebuilding tradition was established by Mirrlees Blackstone of the UK which traced its roots back to the first British licence arranged with Dr Diesel at the end of the 19th century. The Stockport-based company was acquired by the MAN B&W Diesel group from Alstom Engines in June 2000, along with Paxman and Ruston.

Mirrlees Blackstone's final programme—now phased out—was headed by the 800 kW/cylinder MB430L engine, a 430 mm bore/ 560 mm stroke in-line cylinder derivative of the MB430 design which was launched in V45-degree cylinder form in 1985 with a shorter stroke of 480 mm. The two types were respectively produced in six, eight and nine in-line and V12-, V16- and V18-cylinder versions to cover power demands up to 13 144 kW, the in-line engines running at 514 rev/min and the V-engines at 600 rev/min.

The MB430 (Figure 28.13) was introduced with a rating of 665 kW/ cylinder (later increased to 730 kW) and the following key component specification:

Crankshaft: underslung, thin web and high overlap.

Cylinder liners: centri-cast grey iron of heavy section with intensively cooled flanges.

How Many Types Iron Rod Civil Engg
Figure 28.13 Mirrlees Blackstone MB430 design

Cylinder heads: individual, with six holding-down bolts, housing caged exhaust valves and air inlet valves seated on pressed-in seat inserts; valve operation is by Y lever-type gear.

Connecting rods: three-piece construction with a palm-ended shank secured to the large end block with four alloy steel studs, and the halves of the large end block secured together by alloy steel bolts. Large end bearing shells are of steel-backed lead bronze design. Oilways are provided in the connecting rod to facilitate lubrication of the piston pin bearings and deliver a copious flow of cooling oil to the piston.

Pistons: two-piece construction with heat-resistant alloy steel crown and aluminium alloy skirt.

Camshafts: driven by a crankshaft gearwheel via compound intermediate gears; all meshing points are lubricated and cooled by oil sprays; separate cylinder casings house the camshafts and high level fuel pumps.

Engine-driven lubricating oil and water pumps are mounted at the free end of the engine; air manifolds are mounted on the outside of the vee; and turbochargers and intercoolers can be located at either end of the engine.

The MB430 retained many basic features of Mirrlees Blackstone's long-established 400 mm bore/457 mm stroke K Major series which remained in the programme in Mark 3 form, delivering an output of 545 kW/cylinder at 600 rev/min. The design matured from the K-engine of the 1950s, one of the first large medium speed engines in the world, which in its previous Mark 2 form featured a 381 mm bore (Figure 28.14). The connecting rod assembly of a Mark 3 engine is shown in Figure 28.15.

The MB430 design also exploited some concepts introduced for the MB275 series in 1979. This 275 mm bore/305 mm stroke engine was available in six and eight in-line and V12- and 16-cylinder versions covering a power range up to 5070 kW at 1000 rev/min.

Lower power requirements were served by Mirrlees Blackstone's 222 mm bore/292 mm stroke ESL series (Figure 28.16) whose upper output limit was doubled in 1986 by V12- and V16-cylinder models, the latter developing 2985 kW at 1000 rev/min. The programme also embraced five, six, eight and nine in-line cylinder models.

The V-versions tapped the pedigree of the former E range but incorporated several interesting features, including an underslung crankshaft and a belt drive for the lubricating oil and water pumps. The V-models have a 45-degree cylinder configuration, deep main bearing caps, side bolts for added structural stiffness and a central air intake. A simplified rocker arrangement operates four valves (two inlet and two exhaust) through two levers and bridge pieces enclosed within an aluminium cover. The valve gear is actuated by side-loaded camshafts driven from the flywheel end through nitride-hardened gears. The three-piece construction of the connecting rod allows piston withdrawal without disturbing the large end bearing.

Mirrlees Blackstone Engine
Figure 28.14 Cross-section of Mirrlees Blackstone KV Major Mk 2 engine
Mirrlees Blackstone

A pulley and flat belt arrangement for the service pumps, mounted on the engine front, represented a departure from the traditional gear drive used by most enginebuilders. Its adoption was considered beneficial in lower production costs, pump speed flexibility, easier installation and maintenance, and weight and power savings. The belt

comprises a core of endless polyester cords helically wound with a chrome leather friction face covering. A minimum belt life of 10 000 hours was anticipated.

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