The Recent Developments in Marine Diesel Engine - Coursework Example

Insert Name Institution Tutor Date Task Introduction A diesel engine is an engine that has combustion being done in its inner sections. It therefore has internal combustion of fuel. It makes use of compression heat to kindle a fire that burns fuel. This fuel is normally forced into the chamber of combustion in the last step of compression. A diesel engine differs from petrol or gasoline engines in that a gasoline engine uses Otto cycles in which a mixture of air and fuel is put to ignition using spark plugs. Rudolf Diesel who was an engineer from Germany discovered the “diesel cycle.” It is more reliable than any other regular combustion engine because its compression ratio is so high. Ships for example have low speed engines and their thermal efficiency goes beyond 50 percent (Henshall 1996). Engines that use diesel as fuel are made in two kinds which are 4 and 2 stroke. They serve as an effective substitute for unmovable steam engines. These types of engines have found their use in sea going vessels such as submarines and ships since 1910. Later on they were applied also in locomotives electric plants and large trucks. Wartsila marine diesel that has an output of 80 MW is currently the biggest diesel engine in the world(Henshall 1996). Wartsila marine diesel engine Marine diesel engines A marine diesel engine is basically any diesel engine that is built in a marine vessel the vessel uses it to move. This includes the engines used by ships, ferries and other sea going vessels. Mode of operation Only air finds its way in the fuel burning chamber at first. Air compression follows using a ratio of 15-32 that produces pressure of 40 bars. This heavy compression makes the air to heat to 550 degrees centigrade. At such a time fuel is allowed into the burning chamber to mix with the compressed air. It could be somewhere in the piston top or pre chamber. It depends on the engine design, (Henshall 1996). The injector of fuel ensures that fuel is split into tiny droplets and distributed evenly. Heat coming from compressed air causes fuel on the droplets surface to form vapor. This vapor is kindled by heat coming from compressed air inside the combustion chamber. Droplets continually form vapor and burn as they become small to the point where all fuel is consumed. When fuel starts forming vapor it causes a delay and at the time of ignition. When the vapor gets to the burning temperature it causes a knocking sound and a sudden rise in pressure over the piston. Burning gases expand rapidly pushing the piston down and power is supplied to the crankshaft, (Henshall 1996). Increased compression allows combustion to occur without a different system of ignition. This and high ratio of compression raises the efficiency of the engine greatly. As at 2008 many diesel engine systems had new injectors which use piezoelectric wafers that control injection processes in a finer way. Turbochargers with variable geometry have vanes that are very flexible that move as they allow more air to the inside of the engine. This raises the performance of the engine and economizes on fuel. In reference to (Henshall 1996), APC or (Accelerometer Pilot Control) makes use of accelerometer to avail information on the engine’s vibration and noise level then gives instruction to the ECU about fuel injection. These instructions enable the ECU to inject the least amount of fuel that produces silent combustion and at the same time generate the necessary power even when in idle mode. The coming generation of diesel engines is anticipated to employ the use of varying injection geometry. This permits the quantity of fuel to vary across a wide range. Types of marine diesels Diesel engines are made in two classes; that is the 2 stroke and the 4 stroke. Marine propulsion relies on the 2 stroke engine since they are large and offer a better ratio of power to weight and they are economical with fuel. 2 stroke engines are the most powerful in the world. In such engines fuel does not mix with air a head of induction and also the crank case is not actively involved in the cycle, (Henshall 1996). TCA turbocharger MAN Diesels The old 2 stroke design depends on a displacement blower that is driven mechanically to fill its cylinders with air for compression then ignition. The process of charging the cylinders helps in removing combustion gases that remain from earlier power strokes. The archetype of our modern 2 stroke engine is called Detroit diesel. In this the blower puts pressure on a chamber inside the block of the engine called air box. In the 2 stroke process of gas exchange intake and combustion and compression plus expansion should be covered within the same revolution. Again, there should be a clear drop in pressure between the exhaust and the scavenge air in order to get the required flow via the cylinder for proper scavenging, (Henshall 1996). Combustion gases are cleared by scavenge air being blown in the overlap between exhaust and scavenge openings. Two stroke turbochargers need larger quantities of scavenge air and demands for a high efficiency as compared to the 4 strokes. This has in turn resulted in delayed development. In the present day diesels development there needs to be strong cooperation taking place between the manufacturers of turbo chargers and the engine builders. Design aspects Modern engines continue to get new designs in order to eliminate the operational problems of older engines. Modern engines are turbocharged while others have both turbo and supercharging. In the development and advancement of turbochargers many changes have taken place in its design with time. In 1930 turbo charging four stroke diesel engines were developed. This was followed by the first 2 stroke turbo charging engine-Sulzer 6TA48 that came in 1946. In 1956 the very first Sulzer turbo charged marine diesel engine was developed which was 7RSAD76 AND 6SAD72. In the four stroke engine design the process of gas exchange operates by emptying and filling with a small overlap of the valve, (Henshall 1996). The combustion gases are cleared by the displacement of the piston. Early designs of turbo chargers had enough efficiency to provide the required amounts of charge air that was needed by the 4 stroke engine. Diesels don’t have fuel within their cylinders prior to combustion. Therefore it is possible to have the cylinder loaded with 1 bar or more of air without necessitating pre ignition. Turbocharged engines generate bigger volumes of power than the normal ones. More air within the cylinder causes combustion of more fuel hence more power production. Superchargers receive mechanical powering from the crank shaft of the engine while a turbocharger receives power from the exhaust of the engine. Turbo charging increases fuel economy through recovering the heat in the exhaust, raising the level of excess air and raising the ratio of the output of the engine to losses of friction, (Henshall 1996). Comparison of turbo charging system According to (Henshall 1996), 2 stroke engines lack intake and exhaust strokes which are done with the piston at the cylinder bottom. As a result big 2 stroke engines are equipped with piston pumps or turbochargers that are electrical driven at start up. 2 stroke engines of smaller size have turbochargers and a supercharger that is driven mechanically. Since these types of engines generate more power they need attention when designing their components, cooling and lubrication in order to handle that power. Large diesels use water for cooling. Big 2 stroke engines are common prime movers in the world’s fishing in deep seas. Big 4 stroke engines are applied in smaller ships. Two stroke engines are preferred because of their reliability, safety, availability and improved thermal efficiency, (Henshall 1996) Technology holds a lot for the future. For example future designs of engines may have specific power output of a higher level in order to achieve lesser weight per every kW and reduced exhaust emissions. It is also prospected to have upgraded engine reliability with longer periods between overhauls and lower costs of manufacturing. More developments in the design of better engines will include increased scavenge pressure where pressure ratios are supposed to go up to 4.5 with a 22 bars bmep. They will also have improved pressure and efficiency of turbochargers, competitive prices and compact prices. Waste gates and varying turbine area will be used to improve part load operation,(Henshall 1996). Turbochargers incorporated with auxiliary drive - Generator or Motor Units Dual Fuel Engines The modern idea of duel fuel engine design is meant to lower CO2, Sox Nox and other particles from the engine and also to get a fuel alternative by marine operators. This design of engines burns gas and heavy fuel oil. Research has shown that in the future LNG, LPG container vessels and Roro will have gas applications in them. Marine operators may want to invest in duel fuel engines because of the safety and emission regulations, availability and reliability and for the expectation of oil and gas prices future developments. Instead of the boil off gas (BOG) being liquefied and returned to gas tanks LNG vessels that have duel fuel engines can use BOG for propulsion. MAN B&W 2 stroke ME-GI engines use BOG compressor of high pressure. They also use LNG pumps and compressors of high pressure with liquefaction plants, (Henshall 1996). LNG Carrier with ME-GI system Difference between fuel and gas burning engines Gas burning engines have double walled pipes with HC sensors used for shutting down in the event of an emergency. It has a sealing system for oil which takes the oil to the gas valves that separate gas and control oil. There is also a purging engine system that uses inert gas plus a control and safety system that has a hydrocarbon analyser used for checking the content of hydro carbon in air within the 2 walled gas pipes, (Henshall 1996). Safety system In a gas burning engine, all anomalies identified when gas fuel is running result in gas shut down and a shift to HFO operation of fuel. Then there follows a blow out and the gas pipes freed followed by the total system of gas supply. The process of shifting to fuel oil mode has no power losses in the engine. Fuel injection systems Earlier air injection engines had a powerful combustion without increased pressure in the process of combustion. Research is underway for the use of air injection to lower pollution through nitrogen oxides in emissions. With the use of high pressure and advanced technology injectors, modern engines use the system of solid injection applied by Stuart Herbert in the hot bulb engine. Indirect injection engine may be taken as the latest of the hot bulb, low speed ignition engines, (Henshall 1996). Many current diesel engines use a camshaft that rotates at half of the speed of a crankshaft and a single plunger fuel pump of high pressure which the engine crankshaft drives. Each cylinder depends on the plunger to measure the amount of fuel and determine the timing of every injection. The engines have injectors which are basically accurate valves loaded with springs which open and shut at given fuel pressures. Every cylinder has a plunger pump connected to an injector that has a fuel line of high pressure. Slanted grooves control the fuel volume in all combustions. The slanted groove is found within the plunger and it rotates to release pressure. The pressure of fuel helps to keep the valves open. In engines of high speed plunger pumps are found in one unit. ME – GI Injection In this type of injection gas and pilot fuel is injected into the chamber of combustion. There is a gas supply of high pressure, sealing oil supply and controlled supply in order to activate the injection valves for gases. The ME-GI system In the ME-GI system the valve spindle is acted on continuously by the gas at 250 bar. The sealing of the spindle is done by oil sealing at a pressure that is higher compared to gas pressure. The pressure of fuel oil is regularly checked through the GI system in order to identify any problems. High-Pressure Double wall Piping This type of development has double walled gas pipes where by the outer covering pipes hinder gas flow to the machinery space if the inner pipe ruptures. In the design of a gas pipe the branch pipes have added flexibility in order to stand thermal expansion. It can also prevent fluctuations in gas pressure when in operation. For the purposes of purging it has connection for inert gas with 4-8 bars of pressure. If the gas fails, the system of high pressure is releaved from pressure ahead of automatic purging, (Henshall 1996). Fuel gas supply System Design There are 2 100% capacity compressors and pressure ranges from 150-250 bars when conditions are too demanding. Also in the process of laden and ballast passage the variation in BOG is wide. The system has varied suction temperatures, gas composition and pressure in the storage tank. Basic design two 100% compressors Fuel gas compressor Here, the compressor has a capacity controller and is made to deliver BOG of low temperature coming from the atmospheric tank pressure through an inlet with a temperature of -160 degrees. The five stage compressor is propelled by an electric motor, (Henshall 1996). Fuel and power Economy Marine diesels have better efficiency than petrol engines of similar power and this makes them to consume lesser amounts of fuel. MAN S80ME-C7 diesel engines of low speed require 155 gram fuel for every kWh. This is for a conversion efficiency of energy of 54.4 percent. This happens to be the highest change of fuel to power by a combustion engine. The engine can be more efficient compared to gasoline engines when at engine idle and at low power. Diesel engines have no butterfly valve that can close at idle as can be found in petrol engines. This throttle creates parasitic destruction and loss of availability on air coming in and reduces petrol engine efficiency at idle, (Henshall 1996). In marine vessels diesels remain idle and without being attended for hours or many days. Diesels are heavier compared to petrol engines of the same power output. This is necessary since the diesel has to operate on a reduced engine speed. Also, the weight is justified since its parts should be strong in order to resist high operating pressure coming from the big compression engine ratio. Diesels may also be weighty because of the benefits intended from them. They are reliable and have long life spans since they have strong parts although this makes them have a poor power to weight ratio. For marine purposes however reliability is taken to be more important as opposed to high power and light weight. In diesel engines fuel is allowed to inject in before the power stroke. Consequently burning of fuel cannot be complete if there is no enough oxygen. This results into partial combustion forming black smoke if fuel is continuously injected without oxygen for its combustion, (Henshall 1996). In modern diesel and marine engines there is a fuel delivery that is electronic and therefore does regulate the time and amount of fuel delivered. It does this when it changes the injection pulse duration so that it operates without wasting much fuel. In mechanical systems the timing of injection and duration has to be set for efficiency at the expected load and rpm of operation. This means when the engine is running the setting fall short of the ideals if it runs at any other rpm instead of what it is timed for. The electronic injection is able to detect revs in the engine, load, temperature and boost and alter the timing continuously to suit the situation. Modern diesels are stronger for the same out put of power because diesel engines have extended stroke lengths for them to attain the required ratios of compression. Consequently connecting rods and the piston have more weight, (Henshall 1996). This requires more force through the crank shaft and connecting rods in order to change the piston momentum. This quality makes some enthusiasts get increase in power in turbocharged by applying cheap and simple modifications. A same size petrol engine for example may not get such an increase in power unless many alterations are done. This is because the components of the stock cannot support more pressure exerted on them. A marine diesel engine can have some cheap performance tuning since it can support high level pressure, (Henshall 1996). Modifications in such cases should not raise the quantity of air and fuel passing through a diesel since this can raise its temperature of operation something that can cut down its life and necessitate constant servicing. Modern new and light diesel engines with high performance have these problems. This is because they are not strongly built to the standard of the older ones yet they are forced to provide high power, (Henshall 1996). Modern marine engines may have superchargers or turbochargers that help in economizing on fuel and the out put of power. Boost pressure is higher because of knocking and high ratios of compression something that makes them more efficient. The burned gases expand further when in diesel engine cylinders making the exhaust gases cooler. This means turbochargers need lesser cooling and are more reliable. Boost pressure has no limits meaning one can run much boost that can be tolerated by the engine before it can break a part. Diesel engines tend to have a low power out put because the speed is reduced by the combustion time. This problem and others have been taken care of by advanced mechanical technology in modern engines. For example the multistage injectors can shoot some little fuel inside the cylinder to raise the temperature of the chamber of combustion after which the main fuel is delivered, (Henshall 1996). Higher pressures of injection improve the process of atomizing fuel into tiny droplets and electronic control which regulates the length of the process of injection and its timing so that it can suit all temperatures and speeds. Low power and small torque bands are rectified by intercoolers superchargers and turbochargers as well as increasing efficiency of modern engines from like 35% for IDI up to 45% in the latest designs within the last fifteen years. According to (Henshall 1996), injection of fuel however, can cause problems in the maintenance of engines because of the high pressure of fuel used. Some residual pressure may remain within the lines of fuel for along time after the shutting down the engine. Therefore this pressure must be released and the fuel contained. Incase a fuel injector of high pressure is taken away from its normal seat and serviced in the open the person handling it may be injured by hypodermic jet injection. This can happen even with 100 psi pressure. The first recorded injury of such kind happened in 1937 in the process of an engine maintenance. Environmental Aspects Marine diesel engines produce very little amounts of carbon monoxide because they burn fuel in abundant air. They may however release soot through the exhaust. The smoke is made of compounds of carbon which fail to burn due to low temperature resulting from partial atomization of fuel. Such temperatures are found on the walls of the cylinders and on the surface of big oil droplets. This oil has no air for combustion which makes it turn into carbon deposits. Modern engines however have diesel particulate filters that capture carbon particles then they burn them by use of the excess fuel injected inside the engine. Marine diesel engines do produce small amounts of carbon dioxide for every unit distance. The full maximum load of an engine using diesel is shown by black smoke, (Henshall 1996). Beyond this there is no total combustion of fuel. More power can be generated by going beyond this limit but this just happens with reduced efficiency of combustion hence a lot of fuel is consumed. Carbon dioxide emissions per unit load by transport mode When beginning with cold engines the efficiency of combustion of the engine is reduced since the block of the engine takes away heat from the cylinder compression strokes. This results in partial combustion of fuel causing both white and blue smoke with low outputs of power. This happens most in engines with indirect injection because they are not thermally efficient. Modern engines however have electronic injection where injection length and its timing sequence is altered to take care of such problems. Old engines that use mechanical injection have hydraulic and mechanical governors that change the timing, (Henshall 1996). PM10 or 10 micrometer size particles or still smaller ones do cause health problems mostly in cities. Modern diesel engines have filters (diesel particulate filters) that catch black soot. Upon saturation they burn the particles and regenerate themselves. Problems with gases such as sulfur and nitrogen oxides are mitigate by catalytic converters placed within exhausts. Modern marine diesel engines have been designed to use biodiesel in order to minimize the amount of pollution through emissions. Older engines can produce noise resulting from the combustion of fuel. The abrupt ignition of fuel at the point of injection results into a wave of pressure. This noise is called diesel nailing, clatter or knock. This noise is reduced in modern engine designs through pre injection, timing the injection, ratio of compression, indirect injection, use of turbo boost and recirculation of exhaust gas, (Henshall 1996). Marine diesel engines of today have a level of safety that was not there before. For example, before the discovery of turbochargers cooled by water, the number of fires resulting from diesel engines was high to the level of 5 times those caused by gas engines. With the use of turbochargers cooled by water, this rate has gone down tremendously. Today, turbo chargers help in lowering NOx emissions using a maximized low NOx tuning that is based on a specific scavenge air pressure. NOx can be reduced by electronic control engines up to 70% by re circulating exhaust gases and moisturizing by scavenge air, (Henshall 1996). When the thermal efficiency in a diesel engine increases, then reduction of NOx is achieved. Recovery of waste heat achieves up to 60% efficiency in fuel use which reduces HC,CO,PM, SOx, and NOx. Current control methods for emissions; Fuel oil system and homogeniser Trends on control of exhaust emissions Control of emissions is very important to the environment. There to do this engine builders and designers must comply with the maritime industry rules. Engine designers however, face a great challenge of reducing emissions and at the same time reducing fuel consumption, (Henshall 1996). Reducing emissions using 2- stage turbo charging A miller cycle can be used to cool the process of combustion in order to lower NOx emissions. This requires maximum boost pressure which is attained by a 2 stage system of turbo charging. Future targets in marine operations is to lower the impact brought by high efficiency and lowered CO2 emission requirement. 2 emission indexes are under discussion at IMO and an Energy Design Efficiency index (EEDI) together with an Energy Efficiency Operational Indicator (EEOI).EED is useful in evaluating the vessel and engine design while the EEOI guides the operator while developing a good practice on board. Because reducing CO2 emissions almost equals fuel consumption the manufacturer’s goals will approximately correspond with a 30 percent drop in consumption of fuel for every voyage of ships in future. Miller cycle versus standard diesel cycle Maintenance of marine diesel engines With the coming of new technology in the manufacture of marine engines maintenance requirements also change. Maintenance procedures should be followed keenly in order to prolong the engine life. In such engines the engine alarm system should be maintained. An engine survey should be conducted annually. In this survey, inspection is done to look for small problems before they get magnified. Sea water pump impellers should be inspected twice annually. Engine temperatures need to be taken annually with infrared gun and intercoolers cleaned on yearly basis, (Henshall 1996). Every year the pump for sea water should be opened and checked annually. The cooling system needs to be inspected and cleaned after every two years and the engine coolant changed annually. The engines should not be allowed to sit idle for more than 7 days. It should be operated every 5 days. The engine should be warmed up and run at 1500 RPM for five minutes after which it should be shut down. Any engine should not be started before fluid levels are checked. Engines need not be started when throttles are advanced. They should also not be raced until they reach the operating temperature. Prolonged idling of the engine should be avoided. The systems of fuel should be serviced immediately in case of excessive emissions.Sometimes the compressor may be soiled by dust from the surroundings added to oil mist coming from the engine. Such deposits on the turbine are particles from heavy fuel and lubricants from the cylinder that are not combustible. Such things should be removed regularly, (Henshall 1996). The turbo charger should be maintained by subjecting the turbine to dry cleaning at maximum speed for between 24 and 48 hours. The turbine should also be wet cleaned for 48 to 50 hours with water only at a reduced speed. The compressor should be wet cleaned for 25 to 100 hours with water at full speed. Lubrication The oil in the engine needs to be changed regularly probably after every 100 hours. The reason is that large carbon amounts formed as a by product settles in the oil. In case it accumulates in the oil, then its ability to lubricate is retarded. Carbon also hinders the transfer of heat taking back the oil’s cooling function. There are normally cases of sulfuric acid building up in the oil. This accumulation can cause destruction to the bearings, (Henshall 1996). Cooling systems Diesel engines work under a compression from the piston of about 350-550 psi. Because of this great compression pressure is placed on the engine building up heat within a very short time like 1 minute if the cooling mechanism is faulty. Therefore diesel cooling mechanisms are really important. These engines can be greatly damaged even if there is little overheating. Overheating in most cases occurs due to lack of engine inspection and repair of leaks. Cooling systems should not be left to age or else they leak blow off or burst. The systems of cooling should be maintained in a clean state. The coolants used should be in proper mixes and ratios for there to be proper cooling with no corrosion, (Henshall 1996.) Conclusion Technology is growing and many inventions are taking place. Current engines have made a step in tackling the problems that have been there in the past. More research aims at discovering solutions to the present problems like combining efficiency and reduced emissions. The future has solutions for this if only designers and engine developers will work closely, (Henshall 1996). Reference S. H. Henshall, “Medium and High Speed Diesel Engines for Marine Use”, 1996 1st Edition, Institute of Marine Engineers, Mumbai. Read More

When the vapor gets to the burning temperature it causes a knocking sound and a sudden rise in pressure over the piston. Burning gases expand rapidly pushing the piston down and power is supplied to the crankshaft, (Henshall 1996). Increased compression allows combustion to occur without a different system of ignition. This and high ratio of compression raises the efficiency of the engine greatly. As at 2008 many diesel engine systems had new injectors which use piezoelectric wafers that control injection processes in a finer way.

Turbochargers with variable geometry have vanes that are very flexible that move as they allow more air to the inside of the engine. This raises the performance of the engine and economizes on fuel. In reference to (Henshall 1996), APC or (Accelerometer Pilot Control) makes use of accelerometer to avail information on the engine’s vibration and noise level then gives instruction to the ECU about fuel injection. These instructions enable the ECU to inject the least amount of fuel that produces silent combustion and at the same time generate the necessary power even when in idle mode.

The coming generation of diesel engines is anticipated to employ the use of varying injection geometry. This permits the quantity of fuel to vary across a wide range. Types of marine diesels Diesel engines are made in two classes; that is the 2 stroke and the 4 stroke. Marine propulsion relies on the 2 stroke engine since they are large and offer a better ratio of power to weight and they are economical with fuel. 2 stroke engines are the most powerful in the world. In such engines fuel does not mix with air a head of induction and also the crank case is not actively involved in the cycle, (Henshall 1996).

TCA turbocharger MAN Diesels The old 2 stroke design depends on a displacement blower that is driven mechanically to fill its cylinders with air for compression then ignition. The process of charging the cylinders helps in removing combustion gases that remain from earlier power strokes. The archetype of our modern 2 stroke engine is called Detroit diesel. In this the blower puts pressure on a chamber inside the block of the engine called air box. In the 2 stroke process of gas exchange intake and combustion and compression plus expansion should be covered within the same revolution.

Again, there should be a clear drop in pressure between the exhaust and the scavenge air in order to get the required flow via the cylinder for proper scavenging, (Henshall 1996). Combustion gases are cleared by scavenge air being blown in the overlap between exhaust and scavenge openings. Two stroke turbochargers need larger quantities of scavenge air and demands for a high efficiency as compared to the 4 strokes. This has in turn resulted in delayed development. In the present day diesels development there needs to be strong cooperation taking place between the manufacturers of turbo chargers and the engine builders.

Design aspects Modern engines continue to get new designs in order to eliminate the operational problems of older engines. Modern engines are turbocharged while others have both turbo and supercharging. In the development and advancement of turbochargers many changes have taken place in its design with time. In 1930 turbo charging four stroke diesel engines were developed. This was followed by the first 2 stroke turbo charging engine-Sulzer 6TA48 that came in 1946. In 1956 the very first Sulzer turbo charged marine diesel engine was developed which was 7RSAD76 AND 6SAD72.

In the four stroke engine design the process of gas exchange operates by emptying and filling with a small overlap of the valve, (Henshall 1996). The combustion gases are cleared by the displacement of the piston. Early designs of turbo chargers had enough efficiency to provide the required amounts of charge air that was needed by the 4 stroke engine. Diesels don’t have fuel within their cylinders prior to combustion. Therefore it is possible to have the cylinder loaded with 1 bar or more of air without necessitating pre ignition.

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