Twostroke Medium Speed Engines

The medium speed engine market has long been dominated by four-stroke, uniflow-scavenged designs but at one time a number of two-stroke designs enjoyed popularity, notably the Polar loop-scavenged type which ceased production when Nohab introduced its four-stroke F20 range, and Sulzer's uniflow-scavenged ZH40.

WICHMANN's commitment to the two-stroke loop-scavenged trunk piston concept was renewed in 1984 with the launch of its 295 kW/ cylinder WX28 engine (Figure 28.25). The simple 'valveless' approach had been proven in service by the Norwegian company's earlier AX, AXG and AXAG designs. The 280 mm bore/360 mm stroke WX28 covered an output band from 1180 kW to 4735 kW at 600 rev/min with four, five and six in-line and V8-, 10-, 12- and 16-cylinder models.

Development focused on low fuel and maintenance costs with high reliability. The engine was also claimed to be one of the lightest and most compact in its power class. The ability to operate on heavy fuel (180 cSt) under all conditions was another goal. A specific fuel consumption of 188 g/kWh resulted from enhanced scavenging and

Lol Surprise Dibujos Splash Queen Family
Figure 28.25 Wichmann WX28L design

fuel injection systems, and a maximum combustion pressure of 140 bar is underwritten by rugged construction. The mean effective pressure is 13.5 bar.

The valveless cylinder cover is of simple construction, the lack of ducts for hot exhaust gas promoting uniform temperature distribution and low stress. Fastened by eight hydraulically tightened nuts, the cover can be removed in a few minutes and the piston withdrawn in 10 minutes. The connecting rod can be disconnected while leaving the big end bearing on the crankshaft; this feature reduces the necessary removal height.

Wichmann stressed the overall simplicity of the engine and the impact on reliability and serviceability, citing fewer moving parts and hence fewer wearing parts. Separate cylinder lubrication—a standard feature—permits matching of the lubricating oil total base number to the fuel sulphur content. The oil is distributed over the cylinder surface by a hydraulic lubricator via four bores and quills.

Wichmann engines—including the earlier 300 mm bore/450 mm stroke AXAG design—found particular favour in the Norwegian fishing and offshore vessel propulsion sectors. A/S Wichmann became part of the Finland-based Wartsila Diesel group in 1986 and changed its name from Wartsila Wichmann Diesel in January 1994 to Wartsila Propulsion A/S (now Wartsila Propulsion Norway A/S).

The Wichmann 28 engine, which remained in production until 1997, was released with the following specification:

Cylinder block: cast iron monobloc design with integrated crankcase, scavenging air receiver, water manifold and camshaft box; underslung type of crankshaft support.

Crankshaft: fully forged and machined in Cr-Mo steel; dimensionally laid out for 50 per cent power growth potential.

Cylinder liner (Figure 28.26): wear-resistant cast iron alloy; bore cooled with strong backed top section; balanced cooling water flow for efficient temperature control; separate cylinder lubrication through four quills.

Cylinder head: cast iron, valveless, simple design; bore cooled with strong backing to secure efficient cooling and low stress level.

Piston (Figure 28.27): oil-cooled composite design with cast iron skirt and steel crown; ring grooves hardened for low wear rate in heavy fuel operation; integrated small end bearing in full gudgeon pin length.

Connecting rod: drop forged and fully machined; separate large end bearing unit for easy piston withdrawal and low removal height.

Bearings: three-metal steel-backed type, interchangeable with main and crank journal.

Turbocharging: constant pressure system with auxiliary blower in series; the moderate speed auxiliary blower boosts the turbocharger effort to ensure an adequate air supply under all load conditions; the blower is engine driven via low pressure hydraulics using the engine lubricating oil and pump.

Fuel injection system: individual high pressure monobloc pumps with built-in roller tappet; short high pressure pipes and temperature-controlled nozzles for heavy fuel operation.

Fuel Injection Stroke Crank Case
Figure 28.26 Bore-cooled cylinder liner and cover of Wichmann WX28 engine; separate cylinder lubrication is standard
Fit Gudgeon Pin Connecting Rod
Figure 28.27 Composite piston (high alloy steel crown, cast iron skirt and light alloy gudgeon pin support) and connecting rod of Wichmann WX28 engine

Auxiliary pumps: engine gear-driven units for lubricating oil, fresh water and sea water.

Loyal to the two-stroke uniflow-scavenged principle for medium speed trunk piston engines—exploiting air inlet ports in the cylinder liner and exhaust valves in the head—is General Motors' ElectroMotive Division (EMD). The US designer argues better component wear life, reliability and serviceability over four-stroke designs serving the same power range.

EMD's current 645 series and 710 series cover an output band from 785 kW to 3730 kW at 900/1000 rev/min from V8-, 12- and 16-cylinder models (Roots blown) and V8-, 12-, 16- and 20-cylinder turbocharged models. The 645 design has a 230 mm bore/254 mm stroke while the 710 design has the same bore size but a stroke of 280 mm; each is produced in a V45-degree cylinder bank configuration.

The 710G series (Figure 28.28) was launched in 1986 as a longer stroke derivative of the established 645FB range. A more advanced turbocharger (yielding a 10 per cent increase in the overall air-fuel ratio) and larger fuel pump plunger diameter contributed to the higher power rating and lower fuel consumption.

A number of improvements benefited the current 710GB series which offers outputs up to 187 kW/cylinder at 900 rev/min:

• An L-11 liner design for enhanced durability and performance, reduced scuffing and higher wear resistance, and better fuel economy.

• A Duracam camshaft, extending valve train component life and lowering valve vibration.

• A Diamond six-cylinder head with tangent flow fireface, yielding improved cooling and better valve sealing, eliminating core plugs and hence water leaks, and providing hardened valve guides for improved valve and valve guide life.

• Improved unit fuel injector, with new diamond seal design, enhanced check valve and stiffer follower spring.

• A four-pass aftercooler achieving improved thermal efficiency and hence fuel economy, and exhaust emissions reduction.

• A new turbocharger incorporating an external clutch for easier maintenance.

• Lower vibration levels from a new crankshaft and coupling disc balancing technique.

Another medium speed two-stroke design philosophy was pursued for many years by BOLNES of The Netherlands until its acquisition by the Wartsila group and the subsequent cessation of engine production. The company produced the world's smallest two-stroke crosshead engine, the last manifestation being the 190/600 series. The earlier 150/600 design is illustrated (Figure 28.29).

The 190 mm bore/350 mm stroke design delivered a maximum continuous output of 140 kW/cylinder at 600 rev/min on a mean effective pressure of 14.1 bar. The range embraced 3-10 in-line models (excluding a four-cylinder version) and V10-20 cylinder models covering

Top deck cover Camshaft Injector rocker arm Overspeed trip shaft Fuel manifold Injector adjusting link Injector control shaft Injector rack Cylinder test valve

Fuel injector

Cylinder head crab bolt Air inlet ports Air box Water inlet jumper Water inlet manifold Main lube oil manifold

Fork connecting rod Connecting rod basket

Main bearing "A" frame

Main bearing cap Crankshaft

Crankshaft counterweight

Exhaust elbow

Water discharge manifold r Lifting shackle base

Exhaust elbow

Emd 645 Exhaust

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

Exhaust valve rocker arm Exhaust valve bridge Exhaust valve spring Exhaust valve Cylinder head Piston

Thrust washer Piston carrier Piston pin Crankcase Cylinder liner Blade connecting rod Oil drain and vent Air box handhole cover

Piston cooling oil pipe

Piston cooling oil manifold

Oil pan handhole cover Oil pan

Oil level gauge Strainer box

Renewable Energy 101

Renewable Energy 101

Renewable energy is energy that is generated from sunlight, rain, tides, geothermal heat and wind. These sources are naturally and constantly replenished, which is why they are deemed as renewable. The usage of renewable energy sources is very important when considering the sustainability of the existing energy usage of the world. While there is currently an abundance of non-renewable energy sources, such as nuclear fuels, these energy sources are depleting. In addition to being a non-renewable supply, the non-renewable energy sources release emissions into the air, which has an adverse effect on the environment.

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Responses

  • Weronika
    What is as wichmann axag type engine?
    2 years ago

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