Presentation on theme: "Reciprocating Engine Review"— Presentation transcript:
1 Reciprocating Engine Review Back to School – Spring Break is Over!
2 Reciprocating Engines Reciprocating engines power the conventional vehicles that we use for transportation, work, and pleasure.These engines provide power for automobiles, lawn mowers, boats, airplanes, and many other devices used in today’s modern life-style.Most all reciprocating engines used in airplanes are alike. They have the same major systems and use similar construction materials. The differences between these engines are the number and location of cylinders they use.The power is delivered in a back-and-forth movement of a piston. Pistons are sliding pieces within the cylinder of a reciprocating engine that move by and against the expansion pressure of burning fuel.
3 Mechanical System Cylinder Known as the engine’s combustion chamber Where the power is developedThe cylinder is the combustion chamber where the engine’s power is developed.
4 Mechanical System Piston Fits snugly in the hollow cylinder allowing up-and-down linear (straight) motionFit will not allow air or fluid in the cylinderThe piston fits snugly in the hollow cylinder, but not so tightly as to prevent free up-and-down linear (straight) motion.
5 Mechanical System Crankshaft The crankshaft and connecting rod allow for the movement of the propeller.The crankshaft and connecting rod change the piston’s linear motion into rotary (circular) motion required to turn the propeller.The crankshaft is not straight, but has throws (bends) in it that are staggered to obtain a continuing turning motion from the piston power.
6 Mechanical System Connecting Rod Attached to the throws With the crankshaft, they change the direction of the pistons into a circular motionThe connecting rod is attached to these throws.The camshaft is located adjacent to the crankshaft and is connected to the crankshaft through a series of gears.
7 Mechanical System Valves A rocker arm regulates the opening and closing of each valve.Lobes or rings on a camshaft push the rocker armA rocker arm regulates the opening and closing of each valve. Rings or lobes on a camshaft actuate the rocker arm.At the top of each cylinder are two valves, an intake valve and an exhaust valve. The opening and closing of these valves allows the fuel to enter the cylinder and the exhaust gases to leave the cylinder.The camshaft-crankshaft connection will synchronize both of the shafts, the valves, and the piston. This connection makes the parts act at their proper time in sequence of operation.The rings on the camshaft, the cam rings, are made off-round or eccentric. By pressing and releasing the tops of the valves through the rocker assembly in a timed sequence, the cam rings act to ensure that each valve opens and closes at the proper time in the cycle.
8 Spark Plug Internal combustion engines are spark-ignition engines, which require spark plugs to begin combustion, andcompression-ignition engines (diesel engines), which compress the air and then inject diesel fuel into the heated compressed air mixture where it auto-ignites.
9 Mechanical System Cylinder Piston Crankshaft Connecting Rod Valves Spark plugReciprocating engines used in aircraft have certain parts that are vital to their operation. These parts include the cylinder, piston, crankshaft, connecting rod, and valves.
11 Four-Stroke CycleOccurs at the same time in all cylinders, but not on the same stepIgnition sequence of the cylinders called the firing orderThe four-stroke cycle occurs at the same time in the other cylinders of the engine, but no two cylinders are at the same stage of the cycle at the same time.The cylinders are timed to fire in sequence to turn the crankshaft smoothly, transmitting power from it to the propeller.The sequence of ignition of the cylinders in the engines is called the firing order.
13 Types of Reciprocating Engines How to get more horsepower from an engine?(1) Increase the number of cylinders or (2) Increase the size of each cylinderAttention focused on designsTypes of Reciprocating EnginesA constant concern of engine manufacturers is how to get more horsepower from an engine. One solution is to increase the number of cylinders and another solution is to increase the size of each cylinder.The limitations for increasing the size of cylinders are so restrictive that manufacturers have concentrated on the other design method, development of multi-cylinder engines.This method adds smoothness to the power supply because of the added number of power strokes per revolution of the crankshaft.To accommodate additional cylinders, the crankshaft must be lengthened and its number of throws (bends in the crankshaft) must be increased.Manufacturers have come up with several different designs to accommodate the addition of cylinders. The most common designs are in-line, opposed, V and X, and radial.
14 Types of Reciprocating Engines In-line EnginesCylinders are located in a row, onebehind the otherTwo classifications:UprightInvertedIn-line enginesThe cylinders in the engine are located in a row, one behind the other, along the crankcase.If cylinders are located above the crankcase, the engine type is called upright.If the cylinders are below the crankcase, the engine type is called inverted.
15 Types of Reciprocating Engines Opposed EnginesTwo rows or banks of cylinders on each side of the crankshaftRows directly opposite each other called horizontal opposedOpposed EngineOpposed engines have two rows or banks of cylinders, one row on each side of the crankshaft.The rows of cylinders are directly opposite each other, and the engine type is called horizontal opposed.
16 Types of Reciprocating Engines V and X Engine“V” engine features two rows of cylinders setat an angle of about 45°The “X” engine is essentially an opposed “V”engineV and X EngineThe “V” engine features two rows of cylinders set at an angle of about 45°.The “X” engine, which is not as common, is essentially an opposed “V” engine.
17 Types of Reciprocating Engines Radial EngineCrankshaft with onlyone throwOdd number ofcylinders in each bankor rowMaximum number ofis nineRadial EngineFeatures a crankshaft with only one throw.The cylinders are arranged around the crankshaft in a circle so that all the cylinders and connecting rods contribute their power through a single throw. The cylinder whose connecting rod from the piston in this cylinder is designated as the master cylinder. The connecting rod from the piston in this cylinder is called the master rod, and attaches to the throw of the crankshaft.Other connecting rods, called articulating rods, connect the other pistons to the large end of the master rod. The master rod, however, is the only rod that is connected directly to the crankshaft itself.The radial engine always has an odd number of cylinders in each bank or row.The firing order of the four-stroke cycle requires this feature to assure an even delivery of power to the crankshaft. To keep the crankshaft turning smoothly, the radial engine’s cylinders are designed to fire not in numerical order, but according to the best firing order for each engine. By staggering the firing, the engine makes the best use of the power from each cylinder. The maximum number of cylinders in each bank is usually nine. Where more power is needed from an engine, additional banks of cylinders may be added behind the first bank. If more banks are added, the crankshaft must be lengthened to accommodate the master cylinders in each additional bank.These extra banks operate in the same manner as does the original. In effect, a radial engine with two banks of cylinders is two engines working together, one behind the other.
19 Construction of Reciprocating Engines Construction Material of Reciprocating EnginesThe heat generated in an engine is so intense, manufacturers must be careful in choosing materials that can withstand the heat and keep their strength and shape. The cylinder is subject to very high temperatures and pressures. The cylinder barrel, which is the body of the cylinder, and the head must be very strong. The cylinder is made of a high-grade steel alloy machined to very detailed specifications. The inside of the cylinder is highly polished and is very hard. The cylinder is made of cast or forged aluminum alloy and is shrunk onto the cylinder barrel. The shrinking process consists of heating the cylinder head, then screwing it onto the cylinder barrel. The inside of the cylinder head is slightly smaller in diameter than the outside of the cylinder barrel. Heating expands the metal of the cylinder head so that it may be screwed onto the barrel. When the metal cools, the head shrinks to its original size and is locked tightly into place. The valves also are subject to intense heat and pressure. They are made of tungsten steel or chromium steel, which provide strength at high temperatures. The faces of the valves, the portion actually exposed to the heat inside the cylinder, are coated with a thin layer of stellite, which resists burning. Normally, the intake valve is solid, and the exhaust vale is hollow. The hollow center is filled with a salt solution of metallic sodium that conducts the heat away from the valve head. Pistons are made of forged or cast aluminum. Aluminum is used for the pistons because it is strong, has compatible characteristics with steel of the cylinder barrel, and are light enough to stop at the end of the stroke without causing undue stress. Aluminum is also a good heat conductor and is, therefore, easy to cool. The connecting rod is made of steel; and the piston pins, which connect the connecting rod to the pistons, are made of tough nickel steel. The heat on the crankshaft is produced primarily by friction, and not by the action in the cylinder. The crankshaft is subjected to a violent twisting movement, fluid must be made of very strong material to withstand the force exerted on it. The crankshaft is made of chromium steel. The crankcase is usually made of aluminum in smaller engines and of steel in larger engines.
20 Fuels Used in Reciprocating Engines Most common form offuels is hydrocarbonsderived from petroleumGasoline and keroseneoffer several advantagesMix easy with airLow flash pointHigh heat content - powerFuels used in reciprocating enginesThe most common form of fuels is hydrocarbons derived from petroleum. Petroleum is a natural oil pumped out of the earth. The principle hydrocarbon fuels used in aircraft today are gasoline and refined kerosene. Diesel fuel, fuel oil, and lubricating oils are also distilled from petroleum.The gasoline and kerosene used as aviation fuels offer several advantages. They are volatile. They evaporate quickly. They can be mixed easily with air to form a combustible mixture. Gasoline and kerosene have a relatively low flash point.Petroleum-based fuels have low freezing points. This is important when an aircraft is operating in the low temperature of high-altitude flight.Gasoline and kerosene have a high heat content. This means there is much potential energy within these fuels that may be converted to kinetic energy as the fuel burns.Both fuels are relatively stable and can be easily handled using fairly simple safety precautions.They do not deteriorate when stored over long periods of time and are available at reasonable costs.The petroleum from which gasoline and kerosene are derived is found primarily in the United States, Venezuela, the former USSR, Kuwait, Saudi Arabia, Iran, Iraq, and the United Kingdom.