Aircraft reciprocating engine pdf

The rotor revolves on the oil feed bearings. The exhaust gas turbine assembly consists of the turbocharger and waste gate valve. The turbo housing collects and directs the exhaust gases onto the turbine wheel, and the waste gate regulates the amount of exhaust gases directed to the turbine. The waste gate controls the volume of the exhaust gas that is directed onto the turbine and thereby regulates the speed of the rotor turbine and impeller.

Figure 6. Exhaust gas turbine assembly. Figure 7. Waste gate control of exhaust. If the waste gate is partially closed, a corresponding amount of exhaust gas is directed to the turbine. The exhaust gasses, thus directed, strike the turbine blades, arranged radially around the outer edge of the turbine, and cause the rotor turbine and impeller to rotate. The gases, having exhausted most of their energy, are then exhausted overboard. When the waste gate is fully open, nearly all of the exhaust gases pass overboard providing little or no boost.

Some engines used in light aircraft are equipped with an externally driven normalizing system. These systems were not designed to be used as a true supercharger boost manifold pressure over 30 "Hg.

They compensate for the power lost due to the pressure drop resulting from increased altitude. On many small aircraft engines, the turbocharger normalizing system is designed to be operated only above a certain altitude, 5, feet for example, since maximum power without normalizing is available below that altitude.

The location of the air induction and exhaust systems of a typical normalizing turbocharger system for a small aircraft is shown in Figure 8. Figure 8. Typical location of the air induction and exhaust systems of a normalizing turbocharger system. Some ground-boosted sea level turbosupercharged systems are designed to operate from sea level up to their critical altitude. These engines, sometimes referred to as sea level-boosted engines, can develop more power at sea level than an engine without turbosupercharging.

As was mentioned earlier, an engine must be boosted above 30 "Hg to truly be supercharged. This type of turbocharger accomplishes this by increasing the manifold pressure above 30 "Hg to around 40 "Hg. The turbosupercharger air induction system consists of a filtered ram-air intake located on the side of the nacelle. In many cases, the alternate air door can be operated manually in the event of filter clogging. Figure 9. A turbocharger air induction system. Almost all turbocharger systems use engine oil as the control fluid for controlling the amount of boost extra manifold pressure provided to the engine.

The waste-gate actuator and controllers use pressurized engine oil for their power supply. The turbocharger is controlled by the waste gate and waste gate actuator. The waste gate actuator, which is physically connected to the waste gate by mechanical linkage, controls the position of the waste gate butterfly valve.

The waste gate bypasses the engine exhaust gases around the turbocharger turbine inlet. By controlling the amount of exhaust gases that pass through the turbine of the turbocharger, the speed of the compressor and the amount of intake boost upper deck pressure is controlled. Engine oil is also used to cool and lubricate the bearings that support the compressor and turbine in the turbocharger.

Turbocharger lubricating oil is engine oil supplied through the engine oil system. An oil supply hose from the rear of the oil cooler directs oil to the turbocharger center housings and bearings.

Oil hoses return oil from the turbochargers to the oil scavenge pump located on the rear of the engine. The one-way check valve in the oil supply line prevents oil from draining into the turbocharger while the engine is not operating. Piston ring-like oil seals are used on the compressor wheel shaft to prevent the lubricating oil from entering the turbine and compressor housings from the center housing.

The position of the waste gate is controlled by adjusting the oil pressure in the waste gate actuator. Several different types of controllers are used to provide the correct pressure in the waste gate actuator. This is done either by restricting the oil flow or by allowing the oil to return to the engine. The more the oil is restricted, the more pressure is in the waste gate actuator and the more closed the waste gate is. This causes the exhaust gases to pass through the turbine, increasing the speed of the compressor raising the inlet pressure.

The reverse happens if the oil is not restricted by the controllers and boost is reduced. The pressure from the outlet of the compressor of the turbocharger to the throttle is referred to as deck pressure or upper deck pressure.

Figure 10 is a schematic of a sea level booster turbosupercharger system. This system used widely is automatically regulated by three components:. Exhaust bypass valve assembly Density controller Differential pressure controller. Figure Sea level booster turbosupercharger system. When the waste gate is fully open, all the exhaust gases are directed overboard to the atmosphere, and no air is compressed and delivered to the engine air inlet.

Conversely, when the waste gate is fully closed, a maximum volume of exhaust gases flows into the turbocharger turbine, and maximum supercharging is accomplished. Between these two extremes of waste gate position, constant power output can be achieved below the maximum altitude at which the system is designed to operate. An engine with a critical altitude of 16, feet cannot produce percent of its rated manifold pressure above 16, feet.

Critical altitude means the maximum altitude at which, in standard atmosphere, it is possible to maintain, at a specified rotational speed, a specified power or a specified manifold pressure.

A critical altitude exists for every possible power setting below the maximum operating ceiling. If the aircraft is flown above this altitude without a corresponding change in the power setting, the waste gate is automatically driven to the fully closed position in an effort to maintain a constant power output.

Thus, the waste gate is almost fully open at sea level and continues to move toward the closed position as the aircraft climbs, in order to maintain the preselected manifold pressure setting. When the waste gate is fully closed leaving only a small clearance to prevent sticking , the manifold pressure begins to drop if the aircraft continues to climb.

Beyond this altitude, the power output continues to decrease. The position of the waste gate valve, which determines power output, is controlled by oil pressure. Engine oil pressure acts on a piston in the waste gate assembly, which is connected by linkage to the waste gate valve. When oil pressure is increased on the piston, the waste gate valve moves toward the closed position, and engine output power increases.

Conversely, when the oil pressure is decreased, the waste gate valve moves toward the open position, and output power is decreased as described earlier. The position of the piston attached to the waste gate valve is dependent on bleed oil, which controls the engine oil pressure applied to the top of the piston.

Oil is returned to the engine crankcase through two control devices, the density controller and the differential pressure controller. These two controllers, acting independently, determine how much oil is bled back to the crankcase and establishes the oil pressure on the piston.

The pressure- and temperature-sensing bellows of the density controller react to pressure and temperature changes between the fuel injector inlet and the turbocharger compressor. The bellows, filled with dry nitrogen, maintain a constant density by allowing the pressure to increase as the temperature increases. Movement of the bellows repositions the bleed valve, causing a change in the quantity of bleed oil, which changes the oil pressure on top of the waste gate piston.

The differential pressure controller functions during all positions of the waste gate valve other than the fully open position, which is controlled by the density controller. One side of the diaphragm in the differential pressure controller senses air pressure upstream from the throttle; the other side samples pressure on the cylinder side of the throttle valve. Thus, the two controllers operate independently to control turbocharger operation at all positions of the throttle. Without the overriding function of the differential pressure controller during part-throttle operation, the density controller would position the waste gate valve for maximum power.

The differential pressure controller reduces injector entrance pressure and continually repositions the valve over the whole operating range of the engine. Bootstrapping is an indication of unregulated power change that results in the continual drift of manifold pressure.

This condition can be illustrated by considering the operation of a system when the waste gate is fully closed. During this time, the differential pressure controller is not modulating the waste gate valve position. Any slight change in power caused by a change in temperature or rpm fluctuation is magnified and results in manifold pressure change since the slight change causes a change in the amount of exhaust gas flowing to the turbine. Any change in exhaust gas flow to the turbine causes a change in power output and is reflected in manifold pressure indications.

Bootstrapping, then, is an undesirable cycle of turbocharging events causing the manifold pressure to drift in an attempt to reach a state of equilibrium. Bootstrapping is sometimes confused with the condition known as overboost, but bootstrapping is not a condition that is detrimental to engine life.

An overboost condition is one in which manifold pressure exceeds the limits prescribed for a particular engine and can cause serious damage. A pressure relief valve when used in some systems, set slightly in excess of maximum deck pressure, is provided to prevent damaging over boost in the event of a system malfunction.

The differential pressure controller is essential to smooth functioning of the automatically controlled turbocharger, since it reduces bootstrapping by reducing the time required to bring a system into equilibrium. There is still extra throttle sensitivity with a turbocharged engine than with a naturally aspirated engine.

Rapid movement of the throttle can cause a certain amount of manifold pressure drift in a turbocharged engine. Less severe than bootstrapping, this condition is called overshoot. While overshoot is not a dangerous condition, it can be a source of concern to the pilot or operator who selects a particular manifold pressure setting only to find it has changed in a few seconds and must be reset.

Since the automatic controls cannot respond rapidly enough to abrupt changes in throttle settings to eliminate the inertia of turbocharger speed changes, overshoot must be controlled by the operator.

Such a procedure is effective with turbocharged engines, regardless of the degree of throttle sensitivity. Turbocharger system engines contain many of the same components mentioned with the previous systems. Basic system operation is similar to other turbocharger systems with the main differences being in the controllers. The controller monitors deck pressure by sensing the output of the compressor. They have two banks of cylinders staggered on opposite sides of a central crankcase. The design is simple, reliable and easy to maintain.

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Content control:. Reciprocating Engine Description An aircraft piston engine, also commonly referred to as a reciprocating engine or "recip", is an internal combustion engine that uses one or more reciprocating pistons to convert pressure into a rotational motion.

Engine Types Engine design has varied tremendously in the century that has passed since the first powered flight. In-Line Engines The earliest aircraft engines were of the in-line or "straight" variety and had the cylinders in a line, similar to many automotive engines. V-Type Engines A V-type engine is basically the equivalent of two in-line engines joined in a "V" configuration by a common crankshaft. Radial Engines A radial piston engine consists of one or more rows of odd-numbered cylinders arranged in a circle around a central crankshaft.

Horizontally Opposed Engines Horizontally opposed engines are often referred to as boxer or flat engines.

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