Lubricator System for Cutting the Cylinder Oil Bill and Reducing Emissions on MAN B&W Two-StrokeEngines The cylinder lube oil consumption represents a large expenditure for an engine operating with the nominal guiding feed rate and, especially for the large bore engines, even a 0.1 g/bhph reduction in the cylinder oil dosage represents a significant yearly saving for the owner. Cylinder lubrication is therefore an important development theme with the aim of reducing the cylinder lube oil dosage while maintaining a satisfactory piston ring/liner wear rate and maintaining or improving the time between overhauls. Reduced lube oil consumption also has a positive impact on the environment as emissions will be lower. The cylinder oil must be injected into the cylinder at the exact position and time where the effect is optimal, which is not always possible with the conventional lubricators of today. MAN B&W Diesel A/S therefore initiated the development of the new electronic system, the so-called “Alpha Lubrication System” shown in Fig. 1. The development work for the new system was started in 1997, and the prototype entered service on an MAN B&W type 7S35MC engine in 1998. Since then the system has been fine-tuned on MAN B&W’s 4T50MX research engine, and service tests were extended to cover several K90MC engines. The first large bore engine with the new lubricator fitted as standard, a 12K90MC engine, was tested in Korea in September 1999 with very satisfactory results, and the system has now been in service on a number of engines for up to 20,000 hours, with good results. The system is now standard on all MAN B&W two-stroke engines with a diameter bigger than 600 mm and is an option on the smaller engines. The system has been ordered for more than 100 engines, and 30 sets are in service. The new lubricating system is based on the principle of injecting a specific volume of oil into the cylinder, via a number of injectors, for every four (or every five, six, etc.) revolutions. Furthermore, the precise timing ensures that all cylinder oil is delivered directly onto the piston ring pack where it is needed. This can be seen in Fig. 2, which shows the pressure measured in the oil injector Cylinder oil service tank Feed-back sensor Cylinder liner Feed-back sensor Accumulator Lubricator Lubricator Lubricator Cylinder liner Feed-back sensor Accumulator Lubricator Solenoid valve Pump station with stand-by pumps Solenoid valve Solenoid valve Solenoid valve To other cylinders To other cylinders Cylinder lub. oil pipes Electrical connections Tacho signal To other cylinders Alarm system Master control unit and backup control unit Index signal HMI panel Slow-down system Fig. 1: Principle of Alpha Lubricator System 1 [Bar] 20 during a cycle with lube oil injection as well as during a cycle without lube oil injection. The passage of the four piston rings is clearly seen in the pressure signal for the cycle without lube oil injection, and the precision of the new lubricator is obvious. Lube oil injection pressure 15 10 5 Oil quill pressure 0 0 10 20 30 40 50 60 70 80 90 100 [ms] The lubricator itself, Fig. 3, has a small piston for each lubricator quill in the cylinder liner, and the power for injecting the oil comes from the system pressure, supplied by a pump station. A common rail system is used on the driving side, but the injection side has a high-pressure positive displacement system, thus giving equal amounts to each quill and providing the best possible safety margin against clogging of single lubricator quills. Fig. 2: Injection pattern for Alpha Lubricator System Signal for lubrication from control unit Capacitive feedback sensor for control of piston movement Outlets for cylinder liner lube oil points Injection plungers Solenoid valve P A T A P T Cylinder lube oil outlet Spacer for basic setting of pump stroke Adjusting screw Actuator piston 45 bar cylinder lube oil inlet Fig. 3: Alpha Lubricator 2 Fig. 4: 12K98MC-C with Alpha Lubricator For the large bore engines, Fig. 4, each cylinder has two lubricators (each serving five lube oil quills), while the small bore engines, Fig. 5, (with fewer lube oil quills per cylinder) are served by one lubricator per cylinder. The pump station includes two pumps (one operating, the other on stand-by with automatic start up). The computer unit comprises a main computer, controlling the normal operation, a switch-over unit and a (simple) back-up unit. The injection function is controlled by the computer sending an on/off signal to a solenoid valve. A shaft encoder (which can be shared with the PMI system, or timing system on the Intelligent Engine) supplies the necessary timing signal. The amount of oil injected can be adjusted automatically or manually as required, e.g. at load changes, start/stop, at reduced engine load (different modes are available), sulphur % in the fuel, temperature level on liner surface, variation in cylinder oil BN, etc. Pre-lubrication before start can be made manually or be a sequence in the bridge manoeuvring system. Both for marine engines and for engines for power generation purposes, very low feed rates have been demonstrated, with oil consumption down to 0.5 g/bhph. Further reductions in wear rates as well as in feed rates can be obtained by utilising fuel-oil-sulphur-dependent lubrication, a principle for which MAN B&W has applied for a patent. 3 Fig. 5: 7S50MC-C with Alpha Lubricator MAN B&W Diesel A/S Teglholmsgade 41 DK-2450 Copenhagen SV Telephone: +45 33 85 11 00 Telex: 16592 manbw dk Telefax: +45 33 85 10 30
[email protected] www.manbw.dk Copyright © MAN B&W Diesel A/S Reproduction permitted provided source is given. MAN B&W Diesel A/S Reg. No: 39 66 13 14 August 2001 P.384-01.08 4