Modeling and Analysis of a Submarine’s Diesel Engine Lubrication System

Even in today’s age of underwater nuclear power, the majority of the world’s submarines still use diesel engines as their main source of mechanical power, as they have done since the turn of the century. A diesel engine must operate at its optimum performance to ensure a long and reliable life of engine components and to achieve peak efficiency. To operate or keep running a diesel engine at its optimum performance, the correct lubrication is required. General motors V16-278A type engine is normally found on fleet type submarines and is shown in Figure 1. This engine has two banks of 8 cylinders, each arranged in a V-design with 40 degree between banks. It is rated at 1600 bhp at 750 rpm and equipped with mechanical or solid type injection and has a uniform valve and port system of scavenging[1].

Figure 1. GM V16-278A, Submarine Diesel Engine. SOURCE: [1]
Figure 1. GM V16-278A, Submarine Diesel Engine. SOURCE: [1]
Lubrication system failure is the most expensive and frequent cause of damage, followed by incorrect maintenance and poor fuel management. Improper lubrication oil management combined with abrasive particle contamination cause the majority of damage. Therefore, an efficient lubrication system is essential to minimize risk of engine damage.

The purpose of an efficient lubrication system in a submarine’s diesel engine is to:

  1. Prevent metal to metal contact between moving parts in the engine;
  2. Aid in engine cooling by removing heat generated due to friction;
  3. Form a seal between the piston rings and the cylinder walls; and
  4. Aid in keeping the inside of the engine free of any debris or impurities which are introduced during engine operation.

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All of these requirements should be met for an efficient lubrication system. To achieve this, the necessary amount of lubricant oil flow rate with appropriate pressure should circulate throughout the entire system, which includes each component such as bearings, gears,  piston cooling, and lubrication. If the required amount of flow rate does not flow or circulate properly to each corner of the system or rotating components, then cavitation will occur due to adverse pressure and excessive heat will be generated due to less mass flow rate. This will lead to major damage of engine components and reduced lifetime.

To avoid such issues, designers should carefully consider the modeling of engine lubrication system to ensure a long and reliable life for the various components without wasting additional unnecessary oil flow. This type of engine lubrication system can be modeled very accurately and analyzed using 1D thermal-fluid network analysis tool, such as AxSTREAM NET™ developed by SoftInWay.

Using AxSTREAM NET™, designers can evaluate the necessary amount of oil flow rate required for the entire lubrication system which includes bearings, gears, and piston cooling, etc. Additionally, designers can estimate the system pressure levels, temperatures, and heat flows by modeling thermal-fluid network of a submarine diesel engine lubrication system using AxSTREAM NET™. An example of one such configurations of a 16-cylinder submarine diesel engine lubrication system modelled in AxSTREAM NET™ is shown in Figure 2 and 3.

Diesel Engine (Inner Engine) Lubrication System Modeled
Figure 2. Diesel Engine (Inner Engine) Lubrication System Modeled in AxSTREAM NET™

In the inner lubrication system of the engine, oil is supplied to bearings, cylinder wall, and gears as shown in Figure 2. This system consists of bearings, gear components, pistons, cylinder and camshaft. As shown in Figure 2, oil is provided by the lubricating oil engine inlet which is marked in red (1) and flows through main lubricating oil manifold (2) to supply all engine stages. Lubrication flows (3&4) to two oil distributors block (5&6). Then, oil lubricates gears (7-10) and bearings (11-15). Finally, oil drops due to gravity after passing through the entire system and flows out into the sump tank. In AxSTREAM NET™, various elements can be used to model bearings including somewhere the oil flow is determined to provide the desired system cooling.

Engine Oil Supply System Modeled
Figure 3. Engine Oil Supply System Modeled in AxSTREAM NET™

Engine oil supply system provides oil pressurizing, cleaning and cooling (Figure 3). This system consists of sump tank, pump, strainer and cooler. Sump tank (1) collects oil at atmospheric pressure after engine lubrication, pump (2) sucks out oil from sump tank to inject it into engine. Oil is cleaned in strainer (3) and cooled down in cooler (4) since the system is closed. Valves prevent overpressure in the supply system.

The advantage of modeling a lubrication piping network in AxSTREAM NET™ is that it can determine  pressure losses in the system and therefore determine the required pump pressure rise. The solver also predicts hydraulic losses which depends on geometry and sizing of the system such as straight pipes, elbows, bearings, valve, various flow resistance, etc. Designers can also to specify characteristics of equipment (including the pump) and perform calculation dependent upon flow conditions (pump performance map). Thus, in AxSTREAM NET™, various types of flow and heat transfer elements can be accurately modeled for a submarine’s diesel engine lubrication system in 1D shapes that are quite complex while allowing users to create custom components, properties and equations to better suit their needs. Additionally, different types of oils can also be investigated to study the lubrication and cooling potential of the entire system.

To design or analyze pumps, like the one shown in Figure 3’s Engine oil supply system, SoftInWay offers a complete turbomachinery design and analysis tool called AxSTREAM® which can generate optimized designs with less time and effort starting from the specifications. Using this tool, designers can generate thousands of designs from scratch with minimal data available. The flexibility of this software allows a person with basic knowledge of pump design and use of design tools to perform complex pump design and analysis tasks. Example of a centrifugal pump designed using AxSTREAM® is shown in Figure 4.

Centrifugal Pump Designed using AxSTREAM
Figure 4. Centrifugal Pump Designed using AxSTREAM®

Are you interested in learning about how SoftInWay can help you to model or improve your engine lubrication system? or/ to design or analyze a pump using the AxSTREAM Platform? Reach out to us at Info@Softinway.com to schedule a demo or request a trial here

References:

  1. https://maritime.org/doc/fleetsub/diesel/chap1.htm
  2. https://maritime.org/doc/fleetsub/diesel/chap7.htm