Report of Engine Cooling & Exhaust System


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Report of Engine Cooling & Exhaust System

  2. 2. 2TABLE OF CONTENTSNo. Topics Pages1. Introduction 32. Air Cooling System 3-53. Liquid Cooling System 6-104. Straight Stack Exhaust System 10-125. Collector Exhaust System 13-146. Exhaust System with Supercharger 15-187. References 19
  3. 3. 3ENGINE COOLING & EXHAUST SYSTEMSINTRODUCTIONEngine cooling is a system that capable to transfer heat from hot region to coldregion either by conduction or convection in order to cool down the engine. There are twotypes of engine cooling which are air cooled and liquid cooled. While an exhaust system isa system usually piping used to guide reaction exhaust gases away from a controlledcombustion inside an engine or stove. The entire system conveys burnt gases from theengine and includes one or more exhaust pipes. Depending on the overall system design,the exhaust gas may flow through one or more of cylinder head and exhaust manifold, aturbocharger to increase engine power, a catalytic converter to reduce air pollution, amuffler/silencer, to reduce noise.AIRCRAFT ENGINE COOLING SYSTEMSAIR COOLINGFunctionThe burning fuel within the cylinders produces intense heat, most of which isexpelled through the exhaust system. Much of the remaining heat must be removed toprevent the engine from overheating. So air cooled system was installed in motor vehicle tocools down the engine.Basic PrincipleMajority of aircraft piston engine cooling is done by air. Some of them are cooled byliquid. Air cooling is accomplished by air flowing into the engine compartment throughopenings in front of the engine cowling. Baffles route this air over fins attached to the enginecylinders, and other parts of the engine, where the air absorbs the engine heat. Expulsion ofthe hot air takes place through one or more openings in the lower, aft portion of the enginecowling. The outside air enters the engine compartment through an inlet behind thepropeller hub. Baffles direct it to the hottest parts of the engine, primarily the cylinders,which have fins that increase the area exposed to the airflow.
  4. 4. 4Figure 1: Aircraft air cooled systemIn air cooled engine, thin metal fins project from the outer surfaces of the walls andheads of the engine cylinders. When air flows over the fins it absorbs excess heat from thecylinders. Fins on the cylinder head are forged or cast as part of the head. Fins on the steelcylinder barrel are machined from the cylinder barrel forging. Deflector baffles is made fromaluminum sheet, it will fastened around the cylinders direct the flow of air to obtain themaximum cooling effects.Figure 2: Cylinder with baffles for cooling.
  5. 5. 5The air cooling system is less effective during ground operations, takeoffs, go-around, and other periods of high-power, low-airspeed operation. Conversely, high-speeddescents provide excess air and can shock cool the engine, subjecting it to abrupttemperature fluctuations.Operating the engine at higher than its designed temperature can cause loss ofpower, excessive oil consumption, and detonation. It will also lead to serious permanentdamage, such as scoring the cylinder walls, damaging the pistons and rings, and burningand warping the valves. Monitoring the flight deck engine temperature instruments will aid inavoiding high operating temperature.Engine operating temperature can be controlled by the movable cowl flaps locatedon the engine cowling. Cowl flaps are hinged covers that fit over the opening through whichthe hot air is expelled. If the engine temperature is low, the cowl flaps can be closed, so thatit will increase engine temperature. If the engine temperature is high, the cowl flaps can beopen to permit a greater flow of air through the system, so that it will decrease the enginetemperature. But under normal operating conditions in aircraft not equipped with cowl flaps,the engine temperature can be controlled by changing the airspeed or the power output ofthe engine. High engine temperatures can be decreased by increasing the airspeed and/orreducing the power. The oil temperature gauge gives an indirect and delayed indication ofrising engine temperature, but can be used for determining engine temperature if this is theonly means available.Advantages and disadvantages1. Advantagei. Less expensive compare to liquid cooled system.ii. More light-weight.iii. More environment-friendly.2. Disadvantagei. Uneven and unreliable cooling based on airflow.ii. Air-cooled engine that fail generally require a major overhaul.iii. Their maintenance and repair tasks tend to be more frequent and more time-consuming.
  6. 6. 6LIQUID COOLINGThere are few aircraft currently fitted with liquid-cooled engines, but liquid cooling isused extensively in cars. In liquid-cooled engines, the cylinders and cylinder head aredouble walled, or and a liquid is circulated through the jackets. Preventing overheating isone function of the cooling system. It also helps the engine reach its best operatingtemperature as soon as possible. Every engine has a temperature at which it operates best.Below this temperature, ignition and combustion can be difficult. Most engine wear occursduring this warm-up period and most pollution too.The basic coolant use for liquid cooling system is water, but because of the lowertemperatures at altitude, the addition of an anti-freeze agent is essential with aero enginesand a mixture of 70% water and 30% ethylene glycol is normally used. The industry term forthe antifreeze mixture is engine coolant. Some antifreezes use no water at all, instead usinga liquid with different properties, such as propylene glycol or a combination of propyleneglycol and ethylene glycol. Most "air-cooled" engines use some liquid oil cooling, to maintainacceptable temperatures for both critical engine parts and the oil itself. Most "liquid-cooled"engines use some air cooling, with the intake stroke of air cooling the combustion chamber.An exception is Wankel engines, where some parts of the combustion chamber are nevercooled by intake, requiring extra effort for successful operation.Working principleIn this very basic liquid-cooling system, a coolant is stored in a radiator, and in theengine. As the engine heats up, a natural circulation starts, as coolant rises through theengine block by convection. It passes through the top hose, and into the radiator. Inside theradiator, heat is removed from the coolant as it falls from the top to the bottom. When it
  7. 7. 7reaches the bottom, it returns to the engine through the lower radiator hose. This process iscalled thermo-siphon. It was common in older cars which had low-powered engines andhigh, narrow radiators. In modern cars, the engines are more powerful, and radiators arelow and wide, and a there siphon process couldn’t move the coolant quickly enough.Instead, a water pump forces it through passages called water jackets in the engine block. Itcollects heat by conduction, and becomes hot itself. Heated coolant then returns to theradiator for cooling. And the cycle is repeated. Heat is removed from the engine, anddispersed.One function of the thermostat is to shorten the warming-up period. It operatesaccording to coolant temperature. When coolant is cold, it is closed. When a cold enginestarts, coolant circulates within the engine block and cylinder head and through a coolantbypass to the water pump inlet. It can’t get to the radiator. As the engine warms up, thecoolant trapped in the engine gets hotter and hotter. This starts to open the thermostat,allowing hot coolant to flow to the radiator.Components of liquid cooling systems1. RadiatorIt mainly consists of an upper tank and lower tank and between them is a core.The upper tank is connected to the water outlets from the engines jackets by a hosepipe and the lover tank is connect to the jacket inlet through water pump by meansof hose pipes. There are 2-types of cores:i. Tubularii. Cellular as shown.
  8. 8. 8When the water is flowing down through the radiator core, it is cooled partiallyby the fan which blows air and partially by the air flow developed by the forwardmotion of the vehicle. As shown through water passages and air passages, waferand air will be flowing for cooling purpose. It is to be noted that radiators aregenerally made out of copper and brass and their joints are made by soldering.2. Thermostat ValveIt is a valve which prevents flow of water from the engine to radiator, so thatengine readily reaches to its maximum efficient operating temperature. After attainingmaximum efficient operating temperature, it automatically begins functioning. Generally,it prevents the water below 70°C.When the temperature of water increases, the liquid alcohol evaporates and thebellow expands and in turn opens the butterfly valve, and allows hot water to theradiator, where it is cooled.
  9. 9. 93. Water PumpIt is used to pump the circulating water. Impeller type pump will be mounted atthe front end. Pump consists of an impeller mounted on a shaft and enclosed in thepump casing. The pump casing has inlet and outlet openings. The pump is driven bymeans of engine output shaft only through belts. When it is driven water will be pumped.4. Water JacketsCooling water jackets are provided around the cylinder, cylinder head, valveseats and any hot parts which are to be cooled. Heat generated in the engine cylinder,conducted through the cylinder walls to the jackets. The water flowing through thejackets absorbs this heat and gets hot. This hot water will then be cooled in the radiator.
  10. 10. 105. FanIt is driven by the engine output shaft through same belt that drives the pump. Itis provided behind the radiator and it blows air over the radiator for cooling purpose.Advantages and disadvantages3. Advantagesi. Uniform cooling of cylinder, cylinder head and valves.ii. Specific fuel consumption of engine improves by using water cooling system.iii. If we employ water cooling system, then engine need not be provided at thefront end of moving vehicle.iv. Engine is less noisy as compared with air cooled engines, as it has water fordamping noise.4. Disadvantagesi. It depends upon the supply of water.ii. The water pump which circulates water absorbs considerable power.iii. If the water cooling system fails then it will result in severe damage of engine.iv. The water cooling system is costlier as it has more number of parts. Also itrequires more maintenance and care for its parts.AIRCRAFT EXHAUST SYSTEMSEngine exhaust systems vent the burned combustion gases overboard, provide heatfor the cabin, and defrost the windscreen. An exhaust system has exhaust piping attachedto the cylinders, as well as a muffler and a muffler shroud. The exhaust gases are pushedout of the cylinder through the exhaust valve and then through the exhaust pipe system tothe atmosphere.For cabin heat, outside air is drawn into the air inlet and is ducted through a shroudaround the muffler. The muffler is heated by the exiting exhaust gases and, in turn, heatsthe air around the muffler. This heated air is then ducted to the cabin for heat and defrostsapplications. The heat and defrost are controlled in the cockpit, and can be adjusted to the
  11. 11. 11desired level.Exhaust gases contain large amounts of carbon monoxide, which is odorless andcolorless. Carbon monoxide is deadly, and its presence is virtually impossible to detect. Theexhaust system must be in good condition and free of cracks.Some exhaust systems have an exhaust gas temperature probe. This probetransmits the exhaust gas temperature (EGT) to an instrument in the cockpit.The EGT gauge measures the temperature of the gases at the exhaust manifold.This temperature varies with the ratio of fuel to air entering the cylinders and can be usedas a basis for regulating the fuel/air mixture. The EGT gauge is highly accurate in indicatingthe correct mixture setting. When using the EGT to aid in leaning the fuel/air mixture, fuelconsumption can be reduced.For specific procedures, refer to the manufacturers recommendations for leaning themixture.STRAIGHT TYPE EXHAUST SYSTEMStraight exhaust system is means that straight pipe direct connected to the engineand that is why it is called as straight exhaust system. It is also can be defined as theexhaust runs straight from the engine to out from under the car without any muffler orcatalytic converter.STACK TYPE EXHAUST SYSTEMStack type exhaust system is defined as a pipe projecting from an aircraft engineand serving as an outlet for exhaust gases. In other words, short pipes that carry theexhaust gases from the cylinder into the surrounding air and it is also be called exhaustpipe. While short stack means the exhaust system of an aircraft reciprocating engine madeof short pipes that direct the exhaust gases from each individual cylinder of the engine awayfrom the aircraft. Vintage aircraft sometimes have these short stacks on each side of theengine as exhaust. They do are easy to maintain and inspect, have no back pressure andkeep the exhaust valves cool. But a major drawback is that they are not really quiet. This isnowadays not the way to go for everyday use aircraft. Besides, it is generally used on non-
  12. 12. 12supercharged engines and low powered engines where noise level is not too objectionable.Moreover, the short stack system is relatively simple, and its removing and installation thehold-down nuts and clamps.
  13. 13. 13COLLECTOR EXHAUST SYSTEMIn automotive engineering, an exhaust manifold collects the exhaust gases frommultiple cylinders into one pipe. Exhaust manifolds are generally simple cast iron orstainless steel units which collect engine exhaust from multiple cylinders and deliver it to theexhaust pipe. These consist of individual exhaust head-pipes for each cylinder, which thenusually converge into one tube called a collector. The most common types of aftermarketheaders are made of mild steel or stainless steel tubing for the primary tubes along with flatflanges and possibly a larger diameter collector made of a similar material as the primaries.They may be coated with a ceramic-type finish (sometimes both inside and outside), orpainted with a heat-resistant finish, or bare. Chrome plated headers are available but theywill tend to blue after use. Polished stainless steel will also color (usually a yellow tint), butless than chrome in most cases. Another form of modification used is to insulate a standardor aftermarket manifold. This decreases the amount of heat given off into the engine bay,therefore reducing the intake manifold temperature. There are a few types of thermalinsulation but three are particularly common:i. Ceramic paint is sprayed or brushed onto the manifold and then cured in anoven. These are usually thin, so have little insulator properties howeverreduce engine bay heating by lessening the heat output via radiation.ii. A ceramic mixture is bonded to the manifold via thermal spraying to give atough ceramic coating with very good thermal insulation. This is often used onperformance production cars and track-only racers.iii. Exhaust wrap is wrapped completely around the manifold. Although this ischeap and fairly simple, it can lead to premature degradation of the manifold.The goal of performance exhaust headers is mainly to decrease flow resistance (backpressure), and to increase the volumetric efficiency of an engine, resulting in a gain inpower output. The processes occurring can be explained by the gas laws, specifically theideal gas law and the combined gas law.
  14. 14. 14Diamond DA-40 exhausts collector systemCessna exhausts collector system
  15. 15. 15EXHAUST SYSTEM WITH SUPERCHARGERFirstly, supercharger is an air compressor used for forced induction (the process ofdelivering compressed air to the intake of an internal combustion engine) of an internalcombustion engine. A forced induction engine uses a gas compressor to increase thepressure, temperature and density of the air. Superchargers have almost no lag time tobuild pressure because the compressor is always spinning proportionally to the enginespeed.If you can shove more fuel-air mixture into the cylinder of a piston engine, you willproduce more power and thrust. You need compressed air to keep maximum engineperformance at higher altitudes because the density of air decreases with altitude. Airdensity decreases because, as you fly away from the earth, there is less air to pile on top ofthe air below it. A supercharger compresses the air back to sea-level-equivalent pressures,or even much higher, in order to make the engine produce just as much power at cruisealtitude as it does at sea level. With the reduced aerodynamic drag at high altitude and theengine still producing rated power, a supercharged airplane can fly much faster at altitudethan a naturally aspirated one.The Impeller in a superchargers compressor is like the impeller in a hair dryer. Stationaryvanes are added outside the impeller to make the compressor work better.
  16. 16. 16Since the size of the supercharger is chosen to produce a given amount of pressureat high altitude, the supercharger is over-sized for low altitude. The pilot must be carefulwith the throttle and watch the manifold pressure gauge to avoid over boosting at lowaltitude. As the aircraft climbs and the air density drops, the pilot must continuously openthe throttle in small increments to maintain full power. The altitude at which the throttlereaches full open and the engine is still producing full rated power is known as the criticalaltitude. Above the critical altitude, engine power output will start to drop as the aircraftcontinues to climb.There are at least two different ways to drive the compressor. First is by gear itdirectly to the engine’s crankshaft, and second is by letting the gasses that come out theexhaust pipe spin a fan or turbine that in turn, spins the compressor. For this report, we willexplain on exhaust system with supercharger only. It is called turbo-supercharging. Exhaustgases coming out of the engines cylinders are sent through a turbine. The turbine’s shaftthen will turns the compressor.Turbo-supercharging system layoutTurbo-supercharging produces good boost at altitude, the turbine spins faster athigher altitudes because there is less air pressure restricting the flow out of the exhaustpipe. Even if there was no natural tendency for the turbine to spin faster, its speed can beregulated by changing the amount of exhaust that is routed to the turbine.
  17. 17. 17Besides altitude performance, a big advantage of turbo-supercharging is that it canbe added externally to existing engine designs. Many modern automotive applications useturbo-supercharging for boost, just because of this add-on convenience, even though ageared supercharger would be better in automotive applications. One problem withSuperchargers is that because they spin at such a high rate of speed, they also produce alot of heat. Some company’s overcame this obstacle by tapping into the vehicles oil pan tolubricate the gears inside the head unit of the Supercharger to minimize heat and friction.Others use internal belts or self-contained head units where the oil never needs to bechanged.The air itself also becomes hot because you are condensing it. Intercoolers are oftenused to cool the air and create a more densely packed air charge. An intercooler is muchlike a cars radiator. Two common types of intercoolers are Air-To-Air, which uses outside airto cool the air that just passed through the Supercharger, and Air-To-Water, which forcesthe air through a heat exchanger that is cooled by water. Intercooler are not always needed,but are usually found on applications that produce higher levels of boost.You can see the turbo supercharger at the left of the picture is added onto an existing engine. Onthe other side of the compressor is the turbine, which is spun by hot exhaust gases.
  18. 18. 18Another term you will commonly hear among Supercharger conversations is theBypass Valve. When a Supercharger is trying to force air into the engine, but the throttleshaft is closed, a situation called Compressor Surge is created. This can occur duringdeceleration or when the driver is between gears. When the Supercharger is trying to forcethe air into a closed throttle body, and the pressure inside the throttle body is greater thanthe pressure created by the Supercharger, the air tries to force itself backwards into thecompressor. When this happens, the pressure inside the throttle body is released and thecompressor forces the air back through the Supercharger and then back into the throttlebody again, creating a loop. This is where a Bypass valve comes into play. It’s actuated bythe vacuum from the intake, and then releases the excess pressure either into theatmosphere (blow off valve) or back through the compressor.Position of the turbocharger (supercharger driven by exhaust gas)
  19. 19. 19REFERENCES1. Powerplant.pdf2. Reciprocating Machinery Dynamics, Abdulla S. Rangwala, New AgeInternational, 2006.5. Pilot’s Handbook of Aeronautical Knowledge, Federal Aviation Administration(FAA) 2009.6. Aviation Maintenance Technician’s Handbook,(FAA) 2008