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Diesel Engines

The diesel engine has become an integral part of the Navy's propulsion capabilities. It involves the combustion of a suitable fuel inside a cylinder containing a piston, whose motion results from the transformation of thermal energy into mechanical work. Today, diesel engines are used extensively in the Navy, serving as propulsion units for small boats, ships and land vehicles. They are also used as prime movers in auxiliary machinery, such as emergency diesel generators, pumps and compressors.

Over one hundred years ago, in a letter to his former tutor Carl von Linde, Rudolph Diesel wrote: "I have some exciting news; I have found an engine which, according to my calculations, consumes only approximately one tenth of the coal required by our contemporary steam engines." With great conviction, Rudolph Diesel developed the first four-stroke diesel engine from his initial mathematical calculations. Its high efficiency placed everything that had gone before it in the shade. With equal conviction, we have optimized his invention with direct injection and turbocharging. The objectives may have changed somewhat, but the conviction with which Rudolph Diesel worked on his engine is now a major means of ship propulsion and electrical power generation.

The world's very first diesel engine was developed to maturity in Augsburg, Germany between 1893 and 1897, in collaboration with its famous inventor. The following milestones have played a major pioneering role in the development of today's diesel engine:

Between 1901 and 1934 the first four stroke trunk type piston engine was developed, a large diesel engine power plant was established in Kiev, the motor ship Selandia was outfitted with the first marine diesel engine and the first four stroke turbo charged diesel was developed.

In 1935 the first heavy-oil burning four-stroke diesel was manufactured. In 1952 the two-stroke diesel was introduced and in 1987 MAN B&W delivered the largest diesel engine of its time, a 130,000 HP engine for the Queen Elizabeth 2.

Two of the more common small boat engines used in the Navy today are the 6-71 General Motors Detroit Diesel engine and the Westerbeke Model 4-107. The reason for their popularity is that they are reliable and parts are easy to obtain.

Medium-sized combatant ships and many auxiliary vessels are powered by large (~50,000 Bhp ) single-unit diesel engines or, for more economy and operational flexibility, by combinations of somewhat smaller engines. Diesel engines have relatively high efficiency at partial load, and much higher efficiency at very low partial load than steam turbines. They also have greater efficiency at high speeds than any of the other fossil-fueled plants. Thus they require the least weight of fuel for a given endurance. Other advantages include low initial cost and relatively low RPM, the latter resulting in small reduction gears. Additionally, diesel engines can be brought on-line from cold conditions rapidly. They are reliable and simple to operate and maintain, having a long history of active development for marine use.

Large diesel plants have been adapted for use in the Navy on the LSD-41 (Whidbey Island) class (two medium-speed diesel engines drive each of the two shafts). In general, however, the use of diesels on intermediate sized combatants and larger requires that several smaller units be combined to drive a common shaft. This requirement results in severe space and arrangement problems. Among other disadvantages is the fact that periodic engine overhaul and progressive maintenance are required. These result in frequent down periods, which, because of the number of similar units, may not increase the amount of necessary in-port maintenance time, but do decrease the amount of time the ship has full power available while at sea. Finally, the marine diesel has a high rate of lube oil consumption, which may approach 5% of the fuel consumption; thus large quantities of lube oil must be carried.

The moving parts of the diesel engine provide for controlling the elements necessary for combustion and the transformation of combustion to mechanical shaft energy. The major moving components are the crankshaft, piston assembly, connecting rod, camshaft, valves, operating gear, flywheel, vibration dampener and various gears.

For a diesel engine to start, it must turn over fast enough to obtain sufficient heat to ignite the fuel-air mixture. Combustion forces the piston down or outward (power stroke) from rapid expansion of the gases. Some factors that effect the starting of an engine include: ambient temperature, compression in the cylinders from excessive wear (low) or newly overhauled engine (high), load on the engine (attached generator) and proper pre-lubrication of the engine bearings prior to starting.

There are two extremes of diesel engine maintenance and overhaul philosophy: run the engine until it breaks and then repair it (usually at the most inopportune time) or continuously tear it down to inspect and replace worn parts. Neither of these philosophies is cost effective nor do they increase engine availability. Monitoring the operational parameters of a diesel engine by plotting and analyzing their values is a proven way to disclose the mechanical condition of a diesel engine. As engine components wear, the operating parameters gradually change with time. Diesel engine trend analysis is the collection and analysis of diesel engine operating parameters for the purpose of predicting the need for corrective maintenance/overhaul. This data can be analyzed to determine the condition of the engine's internal components and critical support systems. Trend analysis and condition based maintenance are logical methods of determining the need for major engine maintenance actions and has been in use in Navy applications since the late 1960's.

Marine Engine Category Definitions
Category Displacement per cylinder power range (kW) rpm range
1 disp. < 5 liters
(and power > 37 kW)
37 - 2,300 1,800 - 3,000
2 5 < disp. < 30 liters 1,500 - 8,000 750 - 1,500
3 disp > 30 liters 2,500 - 80,000 60 - 900

Marine diesel engines with per-cylinder displacement of 30 liters or more that are installed on vessels flagged or registered in the United States, also known as Category 3 marine diesel engines, are very large engines used primarily for propulsion power on ocean-going marine vessels such as container ships, tankers, bulk carriers, and cruise ships. Category 3 marine diesel engines have not previously been regulated under our nonroad engine programs.

For large ocean-going vessels, it is common for the ship to have multiple engines. The primary purpose of the engines is to provide propulsive power to propel the vessel. Engines are also required to generate electrical power to be used for auxiliary purposes such as navigation equipment, maneuvering equipment, and crew services. Marine engines have traditionally been diesel- or steam-powered engines. Since 1980, virtually all large marine engines built have been diesel.

Category 3 marine engines as compression-ignition (i.e., diesel) engines with a displacement greater than or equal to 30 liters per cylinder. Steam engines are not considered Category 3 engines. Category 3 engines can be incredibly large. These engines are equipped with anywhere between four to 14 cylinders with displacement ranging from 30 liters per cylinder up to 2000 liters per cylinder and output between 2,000 kW to over 100,000 kW. There are two common types of Category 3 engines: "low-speed" (e.g., engine speed of 150 rpm or less) and "medium-speed" (e.g., engine speed of approximately 300 rpm). Low-speed engines are two-stroke models which are connected to a direct drive propulsion system. The mediumspeed engines are typically four-stroke engines (a very small percentage are two-cycle). These engines are commonly connected to an electric drive propulsion system. The electric drive system is actually a large electrical generator that can also be used to generate auxiliary power as well drive the propulsion system.

Another important characteristic of Category 3 diesel engines is that they generally operate on a very low-grade petroleum-based fuel called "bunker" or "residual" fuel. This fuel is the remnant fuel left over from the refinery process of making gasoline, diesel, and other petroleum fuels. It is inexpensive and contains high levels of sulfur and nitrogen. Because of its high level of paraffins, bunker fuel is solid at ambient temperature. Therefore, the fuel has to be heated in order for it to become a liquid which can be combusted in the engine. As a result, vessels using Category 3 engines are equipped with elaborate fuel storage and handling systems.

There is usually a distinction between the engines used for propulsion and the engines used to generate electrical power for navigation equipment (radar, gyrocompass, telecommunications), maneuvering equipment (steering gear, bow thrusters) and crew services (lighting & cooking). The engines used to generate electrical power are typically Category 2 diesel engines (5-30 liters per cylinder). Some vessels, such as refrigerated cargo vessels ("reefers") may require Category 3 engines to meet electric power requirements. Examples of this are the Dole Columbia and Dole Chile which are equipped with MaK M32 engines (39 liters per cylinder) as generators.2 Cruise ships often employ diesel-electric engines, discussed above, that provide both propulsion and power generation. In addition to propulsion and electric power engines, an auxiliary engine is typically installed for emergency use.

Category 3 marine diesel engines are unique among engines in the sense that they are very large and are not typically mass-produced. They also come in a broad configuration of models: varying number of cylinders, engine displacement, power output, and engine speed. Because there are so many different vessel applications and such a large selection of available engine configurations, the engine selection is a major design consideration in the overall design of a vessel. As a result, the engine selected for a specific vessel is often a unique design or configuration that is built specifically for that vessel.

Once a vessel manufacturer has determined the size and output of the engine necessary for a particular vessel design, the engine manufacturer develops the engine on a test bed. After engine development is completed, the engine is assembled and tested. The tests consists of making sure the engine starts and operates properly. Certification testing to demonstrate compliance with the MARPOL Annex VI NOx limits may also occur at this time. The engine is disassembled and shipped to the shipyard where the vessel is to be built. The shipyard or an approved licensed assembler reassembles the engine and fits it into the vessel and connects it the propulsion system. This is typically done with engine manufacturer supervision.

Once the vessel is complete, the shipyard will typically perform a series of three more engine tests. The first is referred to as "light-off," which is when the engine is started for the first time in the vessel. The second engine test is dock testing, where the engine is operated in dock to make sure that all systems are operational. The third test is sea testing, where the vessel is taken out on it's "maiden voyage."

Category 3 engine manufacturers are generally large, multi-national, diversified companies which also produce smaller marine engines, marine propulsion and marine electric generation equipment. In addition, these companies produce engines for other uses such as locomotives and power plants. Many have divisions which manufacture vessels and operate shipyards. A total of 16 companies that manufacture Category 3 marine diesel engines. Four large companies (MAN B&W Diesel, Wartsila/New Sulzer, Catepillar/MaK, and Mitsubishi) dominate the sales of Category 3 engines. These four companies account for nearly 75 percent of medium-speed engine sales and 100 percent of low- speed engine sales. The remaining 25 percent of medium-speed engine sales are distributed among the other 12 engine manufacturers. Category 3 diesel engine manufacturers are located primarily in Europe and Japan. Only one engine company (Caterpillar) which manufactures Category 3 diesel engines is headquartered in the United States. Caterpillar recently purchased MaK located in Kiel, Germany. However, Caterpillar does not manufacture any Category 3 diesel engines in the United States. Therefore, there are no Category 3 engines manufactured in the United States.




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Page last modified: 07-07-2011 12:56:55 ZULU