In a marine propulsor which includes an electric motor with a rotor, a bearing assembly supporting the rotor, and a plurality of propulsor blades and a blade assembly driven by the motor, improved cooling/lubricating system includes an inlet through which coolant/lubricant is supplied to the bearing assembly and the motor, a passage communicating with the inlet through which the coolant/lubricant flows, and an outlet located adjacent the trailing edge of the blade assembly through which the coolant/lubricant is expelled, whereby the expulsion of coolant/lubricant through the outlet provides additional forward thrust to the propulsor. The outlet may be located in the blade hub of the blade assembly or, alternatively, the outlet may comprise a plurality of holes located in the trailing edges of the blades of the blade assembly.
Conventional propulsion
The integrity of the entire propulsion chain from the motive unit (motor or engine) through to the propeller relies on effective sealing systems. Whether keeping oil in hard working line shaft bearings or preventing seawater ingress through the stern tube, correct seal profile and optimised material selection are vital to efficient equipment operation.
The successful operation of marine turbine propulsion equipment depends in no small way on the care used in the design, manufacture, operation and maintenance of the lubrication system. Each has a part in providing for the elimination of contamination that may be detrimental to reliable operation. The most common contaminant is water, the presence of which causes the appearance of rust and other metallic compounds. The chief sources of water are shaft seal leakage, condensation, and oil cooler leakage. The advent of rust-inhibited turbine oils has been of material assistance in suppressing the formation of rust, particularly the magnetic iron oxide type, when a limited amount of water, classified as entrained moisture, is present. The A.S.T.M. rust test has been most valuable in predetermining the ability of turbine oil to offer protection against rusting when entrained moisture is present. But, depending upon quantity and chemical content of the water in the lubrication system, rust-inhibited oils may not offer satisfactory protection. It then becomes necessary to determine the reasons for the water being present and eliminate them. Thus we turn to the mechanical aspects of the propulsion equipment for the final solution of the problem. When the design, manufacturing, installation, and operating factors, are given due consideration by the representatives of the ship owners, shipyards, machinery manufacturers, and oil suppliers, water and associated evils should be absent from the consideration. Only then may the best service be expected from the equipment.
FIELD OF THE INVENTION
This invention relates generally to cooling and lubricating systems for a marine propulsor, and more particularly, to such systems that improve efficiency of the propulsor.
BACKGROUND OF THE INVENTION
Various propulsion systems have been proposed for water-going vessels in which one or more propellers are disposed below the waterline of the vessel for surface vessels or disposed within a portion of the hull of submersible vessels. Typically, the propellers in submersible systems have been driven by diesel power, steam turbines or electric motors mounted within the hull of a vessel. A propeller shaft extends through the hull to the propeller mounted on the shaft outside the hull. Such systems have the disadvantages of shaft vibration and noise radiating from the shaft. Further, leaking around the shaft occurs when the seal becomes loose or worn. Alternative systems have been suggested using shaftless electric motors mounted outside of the hull with only electric power cables passing through the hull. A disadvantage of such a system is that propulsors (electric motors and impellers) occupy almost the entire interior of the tail section. Additionally, traditional shaftless electric motors are either too small to effectively move a vessel or, if large enough, add significant weight to the vessel.
The improved marine propulsor comprises a shaftless electric motor with disk-shaped rotor and stators mounted in the vessel structure with a blade assembly mounted on the rotor. The blade assembly includes a blade hub and propeller blades extending beyond the circumference of the vessel housing. The improved bearing assembly comprises a bearing support, bearing cones circumferentially mounted on the bearing support and a rotating bearing member. The bearing assembly permits water to be introduced into the system through an opening in the bearing support and a gap between the bearing cones. The water supplied by this system cools the rotor and stators of the motor as well as the bearing members. The water also lubricates the rotating components. Thus, the water acting as both coolant and lubricant prevents overheating and excessive wear due to friction.
The pumping forces generated by the rotation of the rotor cause the water to flow through the propulsor. The water in this bearing assembly exits through the gap between the blade hub and the vehicle body on both sides of the hub. This water exiting at the inlet and outlet of the propulsor blades has been found to decrease the efficiency of the propulsor.
Accordingly, the object of the present invention is to provide an improved cooling and lubricating system for a marine propulsor which does not compromise the efficiency of the propulsor, and in which the coolant/lubricant is discharged on the trailing edge of the blade assembly. You may download the environmentally acceptable lubricants (EALS) for use in water boundary propulsion systems here.
Cylinder lubrication in a low-speed main propulsion diesel engine:
Cylinder lubrication For marine diesel engines operating on residual fuels containing sulphur, cylinder lubrication must generally serve the following purposes:
■ Create and maintain an oil film to prevent metal to metal contact between the cylinder liner and piston rings.
■Neutralize sulphuric acid in order to control corrosion.
■Clean the cylinder liner, and particularly the piston ring pack, to prevent malfunction and damage caused by combustion and neutralization residues.
Cylinder lubricating oil for a low-speed main propulsion diesel engine is admitted to each cylinder during the compression stroke. Cylinder lubricating oil, for lubricating the piston rings and the liner, has to be admitted when the piston, piston rings and the liner are in cool condition and the piston is moving upward so that oil can be retained on the piston rings and sprayed by the piston rings on the liner walls. This is only possible during the compression stroke. Otherwise, the piston is hot and if the lubricating oil is sprayed on it, it will evaporate very fast and will not carry out any work of lubrication. At the same time, if lubricating oil is injected during the expansion stroke, i.e. when the piston is moving downwards, it will have a scrapping effect rather than lubrication.
Cylinder Lubrication in four-stroke trunk piston engine:
In four-stroke trunk piston engines, there are a number of different methods for lubricating the cylinder liners and piston rings, depending on engine size and make:
■Splash from the revolving crankshaft
■“Inner lubrication”, where the oil is supplied from the piston side
■“Outer lubrication”, where the oil is supplied by an external, separate cylinder lubricating device from the cylinder liner side.
In a four-stroke trunk piston engine, the cylinder lubricating oil is identical to the engine system oil used for bearing lubrication and cooling purposes.
A small amount of the cylinder lubricating oil by-passes the piston rings and ends up in the combustion space,
where it is “consumed”. However, the piston in a four-stroke trunk piston engine has an oil scraper ring that scrapes most of the oil supplied to the cylinder liner back to the engine’s oil pan, from where it is drained, cleaned and recycled.
Normally, a large, modern, well maintained four-stroke trunk piston diesel engine will consume some 0.3 to 0.5 g/kWh of lubricating oil.
Type of Oil Used in Cylinder Lubricating System
- The cylinder lubricant must be of a higher viscosity so that it can form a good lubricating film between the liner and the piston rings.
- It must also withstand the heat variations in the combustion area and must deal with the combustion products.
- Under normal running conditions this oil will typically be an alkaline cylinder lubricating oil of SAE 50 viscosity.
- The alkalinity is indicated by the TBN (Total Base Number) rating of the lubricant. The TBN value most suitable for the cylinder lubricating oil depends largely on the sulphur content of the fuel used. Typical values for sulphur content of 0.5 to 1% may be between 20 to 25 TBN. For sulphur content over 1.5% the TBN number may be 70 or higher.
Using the Correct Feed Rate for Cylinder Lubrication
Once the correct lubricating oil is chosen the correct feed rate must be established in accordance with the engine builder’s recommendations.
- The feed rate has a critical effect on good engine operation apart from the question of oil consumption. With a too low feed rate the danger of the oil film breaking down causing blow by or additional wear is increased.
- Too high a feed rate is a waste of lubricant and money. The correct feed rate will allow the formation of the lubricating film between the liner and the rings and will give maximum protection at the piston reversal points.
The cylinder oil consumption burette is a useful means of checking the oil consumption of individual lubricator boxes to help ensure that the oil is distributed across the boxes as intended.
The volume between the two internal discs is 1/2 litres. Given the temperature density characteristics of the oil, the actual mass of the oil during its use in engine calibration can be calculated from the oil temperature. Calibration time lies typically between 3 10 minutes depending on the oil consumption rates and the speed/power of the engine, (if the oil feed drive is speed/power dependent).
In slow speed operation, the use of heavy fuel oil with high sulphur content makes the job of the cylinder lubricant very difficult. Even high alkalinity oils cannot hope to neutralise all the sulphuric acids which are produced during combustion.
Effect of Under Lubrication and Over Lubrication of Cylinder:
A correct viscosity is important in order to ensure the spreadability of the cylinder oil, and the applied feed rate and injected amount of oil per stroke are key factors in the delicate balance between under- lubrication and over- lubrication:
■Under-lubrication
If too little cylinder oil is supplied, starvation will occur which might result in corrosion, accumulated contamination from unburned fuel and combustion residues, and in the worst case, metal to metal contact, known as “scuffing”.
■Over-lubrication
If too much cylinder oil is supplied, the loss of fresh, unused oil in the scavenge ports will be high, and the piston rings might be prevented from moving (rotating) in their grooves by the so called “hydraulic lock”. Furthermore, the cylinder liner running surface structure might over time become closed and smooth like a mirror, and will no longer be able to retain the lubricating oil. This is sometimes called “chemical bore polish”, and when alkaline deposit build-up on the piston top land from excessive cylinder oil is in contact with the cylinder liner running surface, it can cause what is sometimes called “mechanical bore polish”. All of these phenomena might eventually result in scuffing.
Acid Condensation in the combustion chamber
The cooling system must be operated so that the piston and cylinder liner temperature is not dropped below the temperature at which the Sulphuric acid may condense on the cylinder liner.
Acid condensation depends on:
- the engine combustion pressure • the liner temperature • the concentration of the sulphur oxides • the humidity of the intake air.
So, to help the lubricant in neutralizing the acid, the engineer must ensure that the temperature of the scavenge air should be maintained in accordance with the manufacturers’ recommendation. Too low a scavenge air temperature will result in condensation with the risk of moisture entering the cylinders; too high a scavenge air temperature will adversely affect the combustion characteristics of the engine.
Engine Running-in
Critical to this lubrication area is the way the engine has been run in at commissioning. A good run in procedure will create a good wear in of the cylinder liner and piston ring. A good gas seal is obtained between them whereby a thin oil film provides reliable and effective lubrication.
The period and method of running in should be decided upon in accordance with the engine manufacturer’s recommendation. Even if only new rings have been fitted the running in procedures should be as near as possible to that recommended for new engines.
The running in recommendation may specify the use of a particular type of lubricant and the feed rate should be high. After running in, the normal cylinder oil will be used and the feed rate gradually adjusted until the recommended feed rate is reached.
So, the cylinder lubricating oil must create a lubricating film between the piston ring and the liner, and must maintain effective lubrication. It must also combat corrosive wear. The use of the correct lubricant and the correct feed rate for the engine load will help to achieve the best result from the lubricant.
Lubrication of Medium Speed Trunk Piston Engine
In medium speed diesel the cylinder is open to the crank case. This means that contamination of the crank case oil by combustion products requires the oil to be different in character to that which may be used in a slow speed engine. Generally, the lubricant must:
* create and maintain effective lubrication between moving components under high mechanical and thermal loads;
* transport solid contaminants from the cylinder to the cleaning devices, such as filters and centrifuges;
* withstand heat; fight contamination, corrosion and wear; resist oxidation and thermal breakdown; keep the engine clean.
Unearth the benefits of GG Friction Antidote – An investment that pays off and your benefits at a glance:
Innovative tribological solutions are our passion. We’re proud to offer unmatched friction reduction for a better environment and a quick return on your investment. Through personal contact and consultation, we offer reliable service, support and help our clients to be successful in all industries and markets.
Profitability:
Switching over to a high-performance lubricant pays off although purchasing costs may seem higher at first, less maintenance and longer vehicles/machinery parts lifecycle may already mean less strain on your budget in the short to medium term.
Continuous production processes and predictable maintenance intervals reduce production losses to a minimum. Consistently high lubricant quality ensures continuous, maintenance-free long-term lubrication for high plant availability. Continuous supply of fresh GG Friction Antidote treated lubricant to the lubrication points keeps friction low and reduces energy costs.
Safety:
Longer lubrication intervals reduce the frequency of maintenance work and the need for your staff to work in danger zones. Lubrication systems can therefore considerably reduce occupational safety risks in work areas that are difficult to access.
Reliability:
GG Friction Antidote treated lubricants ensure reliable, clean and precise lubrication around the clock. Plant availability is ensured by continuous friction reduction of the application. Lubrication with GG Friction Antidote treated lubricants help to prevent significant rolling bearing failures.
Need a good ROI? How about 3,900%?
It may sound too outrageous to be true, but the Institute of Mechanical Engineers estimates every $1,000 spent on proper lubrication yields $40,000 in savings.
INSTANT ROI FOR OPTIMIZING YOUR LUBRICATION REGIMEN
How many kilometers do you travel monthly?
How many hours do you clock monthly?
How many litres of fuel do you consume monthly?
What’s the cost of fuel to you monthly?
How many kilometers or hours do you run per oil change?
How many litres of oil do you consume per oil change?
What’s the cost of oil to you monthly?
What’s the cost of oil filters per oil change to you?
What’s the cost of grease to you monthly?
What’s the cost of fuel filters per oil change to you?
What’s the cost of air filters per oil change to you?
What’s the average frequency of vehicle/machinery replacement to you?
What’s the cost of vehicle/machinery replacement to you?
Would you like to lower your operating costs, improve uptime and increase your company’s profits?
Let’s do the math together … Learn more >>
The information in this literature is intended to provide education and knowledge to a reader with technical experience for the possible application of GG Friction Antidote. It constitutes neither an assurance of your vehicle/machinery optimization nor does it release the user from the obligation of performing preliminary tests with GG Friction Antidote. We recommend contacting our technical consulting staff to discuss your specific application. We can offer you services and solutions for your heavy machinery and equipment.
Locate A GG Friction Antidote Dealer