Diesel Engine in Aviation - Report Example

Name: Tutor: Course: Date: Diesel Engine in Aviation The FADEC is a smart engine system that has full authority in its operations. Its main components include a digital computer and an electronic engine controller. These components have a great many sensors and other peripheral components that enable it to maintain control over several engine operations so as to achieve the desired results. It regulates fuel flow into the port inlets and ensures that spark advance is well timed. It also ensures that the ratio of fuel to air mixture is right and that the ignition timing is well controlled. It therefore eliminates the need for magnetos control of fuel-air mixture (Daya 380). There are two sets of the electronic control unit in a FADEC. The Health Status Annunciator is another component. The different sets of sensors include: the speed sensor, the cylinder head temperature sensor, exhaust gas temperature sensor, the manifold air temperature sensor, the manifold air pressure sensor, fuel pressure sensors and the throttle position switch. The Low Voltage Harness This ensures that connection to all components of the FADEC that are important is established. Apart from the speed sensor, the fuel pressure sensor and the manifold sensor, all the other sensors and the fuel injector coils are connected to this Low Voltage Harness. It also acts as a channel through which information from all sensors that need to be processed and analyzed by the Electronic Control Units flow. The Electronic Control Unit (ECU) This is the central processing unit of the FADEC’s Engine Control System. It consists of two sections; the upper section and the lower section. The electronic circuit board where all data processing activities take place is located in the lower section. The ignition coils, however, that are for spark plugs, are contained in the upper section (there are four coils in each ECU). There are two independent microcontrollers in the lower portion (Electronic Circuit Board) that act as control channels. A single engine cylinder is operated by one control channel, resulting into two cylinders per ECU. Cylinders 1 and 2 (opposing cylinders) are controlled by ECU 1. ECU 2 equally controls the two sets of supposing cylinders 3 and 4. Sensor outputs feed the control channel which in turn compares them to detect any changes. The data from the sensors will then be used by the control channel to calculate the duty cycle that will ensure that the fuel to air ratio is well trimmed as they flow into each cylinder. Evidently now, each cylinder can be sufficiently enriched or leaned by the control channels. What happens if failure occurs on one control channel? This is where the system’s smart back up mechanism springs to life. Failure within an ECU causes the second control channel to take over the operations of the signed cylinder plus the assigned cylinder, ensuring that ignition timing and fuel control are still controlled. Redundancy of critical sensors is taken care of by ensuring that each critical sensor has its identical partner connected to the control channel of a different Electronic Control Unit. What if the two identical sensors fail? Default values are integrated in the synthetic software, ensuring that the FADEC system can work with some standard value to ensure injection of an average value into the fuel cylinder. Health Status Annunciator (HSA) Figure 1: Health Status Annunciator Diesinger (2008) says there are five lights on its display panel and throttle operation switch (WOT). The information provided by the Health Status Annunciator shows the current status of the components of the FADEC system. The system comprises two light display system and additional indicators as can be seen above. The Health Status Annunciator, however, does not caution or give a warning for ALT FAIL or OIL pressure/temperature. A FARDEC WARN suggests that the engine might be at a risk of failing as more than one cylinder could be affected. Immediate action should be taken when this happens. A FARDEC CAUTION shows that almost all of the installed are in good health (99.99%). Immediate action is therefore not required. A bad exhaust gas temperature sensor is the most common example. This is because all these sensors are redundant. A reference to VM1000 should be made each time a caution or a warning is received. This hints to the observer the window that the FADEC sees. The PPWR FAIL indicates that no charging activity is taking place at the Primary Battery. EBAT FAIL usually accompanies this. Drainage will start occurring to both batteries and this will continue for a period of 60 minutes. The secondary battery only powers the Turn Coordinator, the AI and the FADEC. The EBAT FAIL then shows an indication that no charging activity is taking place on the backup battery, and as such the battery or the primary power source can run everything else. There also exists a pump, called the FUEL PUMP. This one will light up when a specific switch is on. This switch is the Fuel Boot Pump. An illumination on this bulb will indicate that the fuel pressure does not meet the 20-40 psi limit or that the fuel pump is being manually operated. It will illuminate for the engine driven fuel pump or the electric current driven fuel pump. WOT (Throttle Position Switch) is below the Health Status Annunciator panel. Whenever the Throttle Position Switch is in full throttle (is contacted), the WOT illuminates. A signal requesting for the supply of maximum power is then sent to the ECU. As a result the fuel to air ratio for Best Power is set through the FADEC, a slave to the ECU (277). The FADEC Ignition System This consists of two spark plugs per cylinder and a harness for high voltage power supply. This utilizes an ignition system that comprises of a waste spark. Here, plugs fire once when compression takes place and also fire once when exhaust takes place. This works to keep the clean always (Totten 56). Cylinders one and two will have their spark plugs fired by the EC 1, while third cylinder and the fourth cylinder will have their spark plugs fired by the EC 2. Figure 2: High Voltage Harness Figure 3: Ignition Control conceptual diagram Power Supplies The system comprises a primary power source and a secondary power source. The primary power source is supplied by a 14 volt, 60 amperes alternator, and a 12 volt, 25 amperes per hour battery of lead acid type. This is usually located after the baggage compartment. The secondary power source is supplied by a 12 volt, 7 amperes per hour battery of lead acid type. There are separate circuits for the primary and the secondary power supplies. They also have separate sets of circuit breakers. When a possible loss occurs in the power supply, the system for battery condition monitoring will illuminate the Health Status Annunciator (HSA) EBAT FAIL or PPWR FAIL in a bid to alert the pilot. The FADEC will always oscillate its connection between the primary power source and the alternator indefinitely. When the alternator fails, FADEC will drain the primary power supply battery until it hits 12 volts and then oscillate between the primary power supply and the secondary power supply after every volt is drained (in an attempt to always connect to the best power source), until all the batteries are drained of power. FADEC can operate for at least one hour while running on emergency or backup battery. This emergency supply only feeds power to the FADEC (TC and AI involved) but is not usable for starting purposes. The FADEC System Redundancy It has two sets of power supplies; the primary power supply and the secondary power supply. These ensure that the system is not caught off guard when power complications arise. It has two sets of control channels within the same Electronic Control Unit. If one control channel fails, the other control channel will not only continue servicing its assigned cylinder, but will also service the cylinder that is affected due to the channel error. Redundancy also applies to all the available sensors where each sensor has an identical partner (Ward 77). This partner is connected to the channel of a different Electronic Control Unit so that a failure in one channel does not prevent the other sensor from delivering the required piece of information. Furthermore, should all the two sensors fail or should their channel to the ECU get damaged, there are synthesized software defaults that the system will use so as to contain the imminent damage. To wrap this session up, we have realized that FADEC utilizes a pair of sensors that are redundant to establish a link to the desired ECU. The electronic control unit then compares these values to default values set, performs some calculations to determine the duty cycle and then use this cycle (pulse width modulation) fuel to air ratio required for each cylinder, the fuel injection timing and the timing for the ignition system for each cylinder. We also realize that FADEC has three power sources; the emergency battery, the primary battery and the alternator. Only one power supply is needed by the FADEC to operate. The FADEC thus greatly simplifies the work of the otherwise busy pilot and is also way ahead of conventional systems in efficient fuel utilization, rising by a whole 15% above them. Figure 4: Fadec Redundancy Low Voltage Harness Figure 5: Low Voltage Harness Advantages of FADEC and Fuel Injection System It sorts out the short comings of the carburetor. FADEC Fuel Injection has the very important feature of doing away with the risks associated with carburetor icing, which, according to Safety Council of UK, is guilty of causing four to six annual accidents in the United Kingdom alone. It also does away with fuel bowl flooding. This overflow can always lead to fuel getting to the engine compartment which might cause a fire or explosion. It optimizes operations for better fuel utilization FADEC optimizes fuel utilization by delicately balancing the ignition timing and fuel mixture to the right proportions (Daya 83). A carburetor is tuned to just one condition. The FADEC system, allowing electronic control of fuel flow, ensures that the fuel/air ratio is just right all the time, reducing the resultant fuel consumption by up to 15%. It has an easy starting procedure One does not need to prime or to apply choke manually when the system is starting and during engine warm up. There is an oil temperature sensor that is fully dedicated and will detect a cold engine and automatically balance the engine mixture for an easy start. As the warming up of the engine continues, this choke systematically fades out. The system’s variable ignition timing works well in cold conditions to achieve easy starting. Usually there is the 10 degrees advance starting that paves the way for a smooth continuous adaptation depending on the required starting conditions. It is easy to operate Using a single lever to achieve simplicity, the FADEC reduces the management tasks of the pilot to a simple selection of the power control that is desired. The pilot can then simply focus on flying. Simple errors such as forgetting or flooding the carburetor are thus avoided. Cleaner and easier installation Having been programmed in the factory, plug and play is the only work done during installation. It eliminates the need to synchronize carburetors and to play around with a needle trying to set the correct revolutions per minute. Single lever control eliminates the need for installation cables and heat box that is usually associated with carburetor engines. Diesel Technology in Aviation The use of diesel engine in aviation has never been very popular. In the late 1920s and in 1930s, airships and aircrafts gave the diesel engines a try, but even then it was not widely adopted. The diesel engine has a specific fuel consumption which gives it an edge over its competitors, and a fuel of relatively higher density. However, the diesel engine contains some inherent disadvantages that outweigh its advantages as compared to turboprop or gasoline- fueled engines. The common avgas has an ever increasing cost and is also facing depletion; factors that have contributed to the resurgence in production of aircraft diesel engine in the recent years. The early diesel aircraft In the early 1920s and 1930s, a number of manufacturers developed the diesel aero engines. Junkers Jumo 205, a moderately successful model, was developed during this period. The air-cooled radial Packard was also developed. These two, however, did not prove to be very useful in World War 2. The Packard radial was the first successful diesel engine to be specifically developed for aircraft purposes. It was laid in the radial format that is air-cooled. The low fire risk feature was the main selling point of this diesel engine up to this point. The aircraft adopting this model took its first flight in 8/9/1928. In the early 1930s, a new player rolled into the market. The Junkers Jumo (two-stroke) opposed piston engine got more clientele than its aero diesel counterparts. It achieved moderate success in “Blohm and Voss Ha 139” and much more even in airstrip applications. The Napier and Son in Britain built the Junkers Jumo 204 which never saw the production level. In Zeppelins, the diesel engine (Dailmer-Benz) was also used. The unsuitability if this engine for military applications did it a great deal of harm and as such the development factories concentrated on jet and gasoline engines. The Petlyakov Pe-8 used in the cold war utilized the Charomskiy Ach-30 diesel engine. However, the efficiency of gasoline engines saw the production of these engines disbanded. Post War Development There was occasional interest in the development of diesel engines after the war. These diesel engines had a relatively low power to weight ratio which saw the turbo prop engines gain much advantage over it. The cheap cost of fuel led to more research, by airliners that are of high speed in nature, in jets and turboprop systems. In the 1990s the demand for these diesel engines hit a record low and they almost faced extinction. Modern Developments Today, however, several factors have come into play and are leading to a shift in the way business has always been conducted. We are seeing the diesel engines becoming more and more popular. To start with, the general aviation aircraft industry has had several new manufacturers developing new designs (Sung 65). Secondly, Avgas has become very expensive in Europe and this has given the diesel engine designers something to think about. Avgas has also become difficult to find in the rural areas as compared to diesel and therefore the availability of diesel is helping it to gain ground. Finally, there have also been tremendous improvements in the automotive diesel industry which has seen the rise in efficiency of these engines and therefore making them more acceptable in the aircraft industry. This is due to improved ratio of power to weight. Certified light planes which are diesel driven are now available. New engines and aircraft design are now being developed by several industries. These majorly run on jet fuel or on automotive diesel (conventional) that are readily available. The Modern Diesel Engine System The only large diesel aircraft engines that still have the two-cycle operating principle today are the Junkers Jumo. These machines were designed and assembled in Germany and are widely applied in airplanes in Germany, for both military and civilian purposes. The Jumo 205 is the model which is best known and it has been built to the tunes of thousands by their factory which is specially equipped. Although there is a centrifugal type blower equipped to it, this engine is not overpriced at all (Totten 117). Construction Details The cylinder block (aluminium alloy) is the power section and the main part of the diesel engine (Junkers Jumo 205). This casting comes with integrated supports which hold the bearings that that slide the crank shafts- two in number- and allow smooth passage of cooling water surrounding the cylinder liners in the duration that they are well placed. In the casting liners we have six machined bores and several guides that make sure that they are correctly aligned. Nitralloy steel forgings machine these liners and locking rings beneath the bores secure them so that upward expansion is possible. A large number of inlet ports which are arranged in rows, exhaust ports (large and eight in number), and a great many grooves which help to ensure that the combustion chamber has a large cooling area have been machined within the linear. To prevent corrosion and rust of the linear, it has been plated with chromium on the outside. The Crankshafts There are two crankshafts which have counterbalances and are six-throw in nature. There are large diameter lead-bronze bushes which are seven in number that support these crankshafts. The drive is transmitted to the propeller shaft three gear wheels that are intermediate by the spur gear wheels which are attached at the front ends to the flanges. Mounting of intermediate gear wheels is done on the roller bearings and a cover plate encloses the gear train entirely. Bearings meant for the shaft of the propeller are also contained in the cover plate. A hydraulic vibration pumper that allows for circulation of pressurized lubrication oil between damper oil paddles and the in house recesses within it gets mounted atop the intermediate gear wheel. A splined flexible shaft connects the propeller to the damper wheel. The Pistons Aluminum alloy forgings are used to machine the pistons. They possess strange long skirts with a 2:1 ratio of length to diameter. There is a specially made heat resistant fire-plate attached by four lengthy anchor bolts to every crown of every piston. These bolts have strong compression springs fitted to them in order to ensure that the unusual bimetal expansion is well compensated. Atop the piston pin are four fittings of compression rings and the skirt bottom has an oil scrapper ring. The fire plate has its lower edge surrounded with a fire plate, which in turn rests upon Niresist insert cast on all piston walls. The L-section design of the fire ring enables the combustion gases to expand it outward, sealing it on the wall of the cylinder. This ensures that compression rings are protected from the hot combustion gases hat flame and ensures that no gas leaks past them. The Connecting Rods The I-section connecting rods have chrome nickel steel as their genetic makeup. At their small ends quill bearings are used while at their big ends we find bushings of aluminium alloy applied. There is a hollow, fixed type piston pin used. Chrome nickel is used to make the shaft propeller. The roller and the ball thrust bearings support the mid-point section of the steel while a needle bearing takes care of the inner end. The gear train ensures that there is a reduction drive of1.58:1 on the shaft propeller. The Blower The work of the blower is to supply the cylinders with air for scavenging and give them an air charge filling. This blower has an attachment to the cylinder block rear where gearing drives it from the crankshaft (lower). This blower works on centrifugal properties and has an impeller which is disk shaped and has tangential blades to its hub hanging on its two sides. The intake that draws air is large and screened. This air undergoes a compression of 5lb per square inch pressure and flows along the two cylinder into inlet ports through manifolds. A shutter at the intake of the blower is used to regulate the bower output. Between the blower impeller and the drive shaft lies a slipping clutch that offers protection from abrupt overloads. Should the speed of the engine crankshaft increase rapidly with the throttle opened, there will be a slipping of the clutch, a process that will continue until the two masses that rotate finally get a safe ratio between them. The same story happens for closed engine throttle. This is very important for diesels because they can stop so quickly due to their property of high compression. The Lubrication System There are two injection pumps (high pressure) and four injectors within the injection system for the fuel for every engine cylinder. There are six pumps arranged along either cylindrical block side. Here, two camshafts that are driven at the intermediate gear wheel gear trim centre actuate these pumps. The pumps are run at the speed of the crankshaft in order to match with the engine’s two-cycle functioning. Each set operates independently and can an entire engine running at full load. The camshaft covers and the pumps can be easily demounted from the covers for servicing. The available two injectors get screwed into those cylinder blocks all the way through to the cylinder liner at 90 degrees between the two cylinders. To achieve even fuel distribution, a similar arrangement is made two injectors on the two sides of the block of cylinder. There are two-hole nozzles on the injectors which ensure that fuel is sprayed in the chamber of combustion fan-wise. These injection pumps go through very strenuous duties. There is a simultaneous operation between the four pump injectors and the two pumps and a rate of 37 injections every second is delivered as the engine rotates at 2200 revolutions per minute. Fuel pressure in the pumps gets raised from zero to approximately 8,000 lb. per sq. in every period of injection, only to be returned back to zero. The accurate metering and the controlled timing of small fuel charge get conducted at the same time. Accessories and the cooling system A pump that is centrifugal by nature circulates the engine’s cooling water. There are passages beneath the cylinder liners into which water gets pumped and achieves an upward circulation into passages fitted with outlets at both sides of the cylindrical block. There is also an auxiliary tank that is provided to collect the condensate of any formed steam in the process. This then finds its way back to the system. A dry diesel Jumo 205-E (700 h.p) engine weighs 1,260 lb. When filled, the system weight of 290 lb adds to the engine weight (1,260). Accessory drives are contained at the engine’s rear side. Two tachometers can be attached to the upper crankshaft outlets. The electric inertia starter or one of cartridge type also have provisions. The tail shaft which is has attachment to lower crankshaft has provisions for vacuum pumps, air compressors or electric generators. There is an electric starter (Bosch type) which ensures a smooth and quick engine start. There is also an attachment for a small atomizer that can spray gasoline, lubricating oil and ether into the manifolds for air intake when the engine needs to get started in cold weather. The Fuel Injection System design The Jumo 205 Diesel (junkers) pumps for fuel injection are single unit type and individual. The plunger, the housing, detachable barrel, roller cam arm and double fuel discharge valves in the barrel up the pressure chamber. The simplified control mechanism that allows the plunger to be slightly rotated within the barrel so as to regulate pump output is also implemented. The design of the plunger stroke keeps it constant and the pump can also vary the amount of gas fuel that the pressure chamber admits before compression. The angular cut in the upper end of the plunger has the annular groove slightly lowering down around it. A vertical hole and some tiny horizontal holes connect the plunger’s upper surface to the annular groove. There is a row that contains inlet ports in the upper barrel section within the pressure chamber that enable communication with the housing’s suction chamber. The suction chamber also receives communication from the outlet ports down the barrel. Merits of Diesel cycle Engine The diesel fuel has low flammability and is available worldwide. This is great considering that gasoline will face extinction in the near future. “DeltaHawk” has managed to unleash an engine that improves efficiency by up to 75%. Diesel provides more range per unit volume. It does not have the ignition system and this greatly reduces interference with communication systems and navigation systems. Its power operation uses single lever which is very simple. Applications of diesel technology in aviation Reversible diesel engines were responsible for propelling the “LZ 130 Graft Zeppelin II” and the “zeppelins LZ 129 Hindenburg”. The shifting gears that were placed on the camshaft were used to change the direction of operation of these machines. It was possible to stop the engines, to change them over and to bring them to full power (reverse mode) in a period below 60 seconds. The ill fated R101 (this plane crashed in 1930) used an aero diesel engine called the Beardmore Tornado. Out of its five engines, two could be reversed by adjusting a lever placed on the camshaft. The V-4 Turbo Diesel engine is now operational and it offers a host of advantages such as smoothness, reduction of overcooling, high durability, reliability, small size and light weight. Works Cited Daya, M. Handbook of maintenance management and engineering. London: Springer, 2009. Print. Diesinger, Andreas. Systems of commercial turbofan engines an introduction to systems functions. Berlin: Springer, 2008. Print. Sung, Ho. Optimal maintenance of a multi-unit system under dependencies. S.l.: Proquest, Umi Dissertatio, 2011. Print. Totten, George E. Fuels and lubricants handbook technology, properties, performance, and testing. West Conshohocken, PA: ASTM International, 2003. Print. Ward, Thomas A.. Aerospace propulsion systems. Singapore: John Wiley & Sons, 2010. Print. Read More