Reciprocating Engine Induction Systems PDF

RECIPROCATING ENGINE AVIA 1065 Intro 1 Reciprocating Engine Induction Systems Basic Carburetor Induction System The carburetor air filter, shown in Figure 3-6, is...

RECIPROCATING ENGINE AVIA 1065 Intro 1 Reciprocating Engine Induction Systems Basic Carburetor Induction System The carburetor air filter, shown in Figure 3-6, is installed in the air scoop in front of the carburetor air duct 2 Reciprocating Engine Induction Systems Basic Carburetor Induction System Its purpose is to stop dust and other foreign matter from entering the engine through the carburetor The screen consists of an aluminum alloy frame and a deeply crimped screen, arranged to present maximum screen area to the airstream There are several types of air filters in use including paper, foam, and other types of filters 3 Reciprocating Engine Induction Systems Basic Carburetor Induction System Most air filters require servicing at regular intervals and the specific instructions for the type of filter must be followed. [Figure 3-6] 4 Reciprocating Engine Induction Systems Basic Carburetor Induction System The carburetor air ducts consist of a fixed duct riveted to the nose cowling and a flexible duct between the fixed duct and the carburetor air valve housing The carburetor air ducts normally provide a passage for outside air to the carburetor Air enters the system through the ram-air intake The intake opening is located in the slipstream so the air is forced into the induction system giving a ram effect to the incoming airflow 5  Basic Carburetor Induction System The air passes through the air ducts to the carburetor. Reciprocating Engine The carburetor meters the fuel in proportion to the air and mixes the air with the correct amount of fuel. Induction Systems The throttle plate of the carburetor can be controlled from the cockpit to regulate the flow of air (manifold pressure), and in this way, power output of the engine can beh controlled. 6 Reciprocating Engine Basic Carburetor Induction Induction Systems System Although many newer aircraft are not so-equipped, some engines are equipped with carburetor air temperature indicating systems which shows the temperature of the air at the carburetor inlet. If the bulb is located at the engine side of the carburetor, the system measures the temperature of the fuel/air mixture. 7 Reciprocating Engine Induction Systems Induction System Icing A short discussion concerning the formation and location of induction system ice is helpful, even though a technician’s not normally concerned with operations 8 that occur when the aircraft is in flight  Induction System Icing Technicians should know something about induction system icing because of its effect on engine performance and troubleshooting. Reciprocating Even when an inspection shows that everything is in proper working order and the engine performs perfectly on the ground, induction system ice can cause an Engine Induction engine to act erratically and lose power in the air. Systems Many engine troubles commonly attributed to other sources are actually caused by induction system icing 9  Induction System Icing Induction system icing is an operating hazard because it can cut off the flow of the Reciprocating fuel/air charge or vary the fuel/air ratio. Ice can form in the induction system while an aircraft is flying in clouds, fog, rain, Engine Induction sleet, snow, or even clear air that has high moisture content (high humidity). Induction system icing is generally classified in three types: Impact ice Systems Fuel evaporation ice Throttle ice 10  Induction System Icing Heat is usually obtained through a control valve that opens the induction system to Reciprocating Engine the warm air circulating in the engine compartment and around the exhaust manifold. Improper or careless use of carburetor heat can be just as dangerous as induction Induction Systems system ice. Increasing the temperature of the air causes it to expand and decrease in density.  Induction System Icing Reciprocating This action reduces the weight of the charge delivered to the cylinder and causes a noticeable loss in power because of decreased volumetric efficiency. Engine Induction In addition, high intake air temperature may cause detonation and engine failure, especially during takeoff and high power operation. Systems Therefore, during all phases of engine operation, the carburetor temperature must be controlled to give the greatest protection against icing and detonation. Reciprocating Engine Induction Systems Induction System Icing When there is danger of induction system icing, the cockpit carburetor heat control is moved to the hot position. Throttle ice or any ice that restricts airflow or reduces manifold pressure can best be removed by using full carburetor heat. If the heat from the engine compartment is sufficient and the application has not been delayed, it is only a matter of a few minutes until the ice is cleared. 14  Induction System Icing When there is no danger of icing, the heat control is normally kept in the Reciprocating Engine “cold” position. It is best to leave the control in this position if there are particles of dry snow or ice in the air Induction Systems To prevent damage to the heater valves in the case of backfire, carburetor heat should not be used while starting the engine 15  Induction System Icing Reciprocating Engine during ground operation restrict the use of carb heat Induction Systems The air is unfiltered and the risk to engine damage increases 16  Induction System Icing Reciprocating Impact ice Snow or ice in the air Engine plugs the induction system by packing into the pipe or Induction filter Fuel evaporation ice Systems The air cools as the fuel vaporizes inside the induction system (close to the point of atomization) If this air falls below freezing and moisture is present ice forms on the discharge nozzle and areas downstream restricting the airflow to the engine causing 17 it to quit if not corrected  18 Reciprocating Engine Induction Systems Induction System Icing Throttle ice the temperature of the air behind the throttle plate drops do to the low pressure area formed If this air falls below freezing and moisture is present ice forms on the throttles and nearby units restricting the airflow to the engine causing it to quit 19 Reciprocating Engine Induction Systems Induction System Filtering Dust and dirt can be a serious source of trouble to an aircraft engine Dust consists of small particles of hard, abrasive material that can be carried by the air and drawn into the engine cylinders It can also collect on the fuel-metering elements of the carburetor, upsetting the proper relation between airflow and fuel flow at all engine power settings It acts on the cylinder walls by grinding down these surfaces and the piston rings 20 Reciprocating Engine Induction Systems Induction System Filtering Then, it contaminates the oil and is carried through the engine, causing further wear on the bearings and gears. In extreme cases, an accumulation may clog an oil passage and cause oil starvation. Although dust conditions are most critical at ground level, continued operation under such conditions without engine protection results in extreme engine wear and can produce excessive oil consumption. Reciprocating Engine Induction Systems Induction System Filtering 21 Reciprocating Engine Induction Systems Induction System Filtering 22 Reciprocating Engine Induction Systems Induction System Filtering Some installations have a spring- loaded filter door which automatically opens when the filter is excessively restricted. This prevents the airflow from being cut off when the filter is clogged with ice or dirt. Other systems use an ice guard in the filtered-air entrance. The ice guard consists of a coarse-mesh screen located a short distance from the filtered- air entrance 23 Reciprocating Engine Induction Systems Induction System Filtering In this location, the screen is directly in the path of incoming air so that the air must pass through or around the screen. When ice forms on the screen, the air, which has lost its heavy moisture particles, passes around the iced screen and into the filter element. The efficiency of any filter system depends upon proper maintenance and servicing. Periodic removal and cleaning of the filter element is essential to satisfactory engine protection. 24 Reciprocating Engine Induction Systems Induction System Inspection and Maintenance The induction system should be checked for cracks and leaks during all regularly scheduled engine inspections. The units of the system should be checked for security of mounting. The system should be kept clean at all times, since pieces of rags or paper can restrict the airflow if allowed to enter the air intakes or ducts. Loose bolts and nuts can cause serious damage if they pass into the engine 25 Reciprocating Engine Induction Systems Induction System Inspection and Maintenance Foam type air filters should be checked regularly if dirty or does not have the proper oil film Cleanable element? Yes, remove and clean the filter element No, replace with a new element after it has dried, Recoat with the recommended oil or compound excess fluid should be squeezed out (don’t wring out) before the filter element is reinstalled. Paper-type filters should be inspected and replaced as needed 26 The End 27 Engine Fuel and Fuel Metering Systems AVIA-1065 28 https://www.youtube.com/watch?v=gIdXLMVP6VU Aircraft Engines ERAU 03 29 Engine Fuel and Fuel Metering Systems Fuel/Air Mixtures Gasoline and other liquid fuels do not burn at all unless they are mixed with air If the mixture is to burn properly within the engine cylinder, the ratio of air to fuel must be kept within a certain range It would be more accurate to state that the fuel is burned with the oxygen in the air Seventy-eight percent of air by volume is nitrogen, which is inert and does not participate in the combustion process, and 21 percent is oxygen 30 Engine Fuel and Fuel Metering Systems Fuel/Air Mixtures – Heat is generated by burning the mixture of gasoline and oxygen – Nitrogen and gaseous byproducts of combustion absorb this heat energy and turn it into power by expansion – The mixture proportion of fuel and air by weight is of extreme importance to engine performance 31 Engine Fuel and Fuel Metering Systems Fuel/Air Mixtures Heat is generated by burning the mixture of gasoline and oxygen Nitrogen and gaseous byproducts of combustion absorb this heat energy and turn it into power by expansion The mixture proportion of fuel and air by weight is of extreme importance to engine performance 32 Engine Fuel and Fuel Metering Systems Fuel/Air Mixtures The composition of the fuel/air mixture is described by the mixture ratio When aircraft fly at altitude, what happens to the air? Air Density decreases Why? less air pushing down from above, and gravity is weaker farther from Earth's center https://flexbooks.ck12.org/cbook/ck-12-middle-school-earth-science-flexbook-2.0/section/10.3/primary/lesson/pressure-and-density-of-the-atmosphere-ms-es 33 Engine Fuel and Fuel Metering Systems Fuel/Air Mixtures Because air is a gas, its molecules have a lot of energy Air molecules move a lot and bump into things For this reason, they exert pressure Air pressure is defined as the weight of the air pressing against a given area 34 Engine Fuel and Fuel Metering Systems Fuel/Air Mixtures Like density, the pressure of the air decreases with altitude There is less air pressing down from above the higher up you go Look at the bottle pictured below (Figure below). It was drained by a hiker at the top of a mountain. Then the hiker screwed the cap on the bottle and carried it down to sea level. At the lower altitude, air pressure crushed it. Engine Fuel and Fuel Metering Systems Fuel/Air Mixtures If we put fuel and air into the cylinder at ground level, what happens to the fuel air mixture when we go up in altitude? What would we need to adjust when we are at higher altitudes? Can we leave the fuel to air ratio the same as we climb? No, Ratio of fuel air needs to be adjusted How would we need to adjust the fuel/air ratio? Lean it out for altitude Less air means we need less fuel Lean=Less fuel Engine Fuel and Fuel Metering Systems Fuel/Air Mixtures The ratio 12:1 a and fuel/air ratio of 0.083 describe the same mixture ratio 12 ÷ 1 = 0.083 37 Mixtures of air and gasoline as rich as 8:1 and as lean as 16:1 will burn in an engine cylinder, but beyond these mixtures, either lean or rich blow out could occur The engine develops maximum power with a mixture of approximately 12 parts of air and 1 part of gasoline by weight Engine Fuel and Fuel Metering Systems Fuel/Air Mixtures From a chemist’s point of view, the perfect mixture for combustion of fuel and air would be 0.067 pounds of fuel to 1 pound of air (mixture ratio of 15:1). The scientist calls this chemically correct combination a stoichiometric mixture (pronounced stoy-key-o-metric) With this mixture (given sufficient time and turbulence), all the fuel and all the oxygen in the air is completely used in the combustion process 38 Engine Fuel and Fuel Fuel/Air Mixtures If, with constant airflow, the Metering Systems mixture is leaned below 0.067, (15:1) fuel/air ratio power and temperature decrease together This time, the loss of power is not a liability but an asset The purpose in leaning is to save fuel. Air is free and available in limitless quantities This is best economy-A measure of the economical use of fuel is called specific fuel consumption (SFC), which is the fuel weight in lbs/hour/horsepower SFC = lbs fuel/hour horsepower 39 Engine Fuel and Fuel Metering Systems Fuel/Air Mixtures The best economy fuel/air ratio varies somewhat with rpm and other conditions, but for cruise powers on most reciprocating engines, it is sufficiently accurate to define 40 this range of operation as being from 0.060 to 0.065 fuel/air ratios on aircraft where manual leaning is practiced. (16:1-15:1) Below the best economical mixture strength, power and temperature continue to fall with constant airflow while the SFC increases Engine Fuel and Fuel Metering Systems Fuel/Air Mixtures As the fuel/air ratio is reduced further, combustion becomes so cool and slow that power for a given manifold pressure gets so low as to be uneconomical 41 The cooling effect of rich or lean mixtures results from the excess fuel or air over that needed for combustion Internal cylinder cooling is obtained from unused fuel when fuel/air ratios above 0.067 are used (richer) The same function is performed by excess air when fuel/air ratios below 0.067 are used (leaner) 42 Engine Fuel and Fuel Metering Systems 43 Engine Fuel and Fuel Metering Systems Fuel/Air Mixtures An engine running near full power requires a rich mixture to prevent overheating and detonation Since the engine is operated at full power for only short periods, the high fuel consumption is not a serious matter 44 Engine Fuel and Fuel Metering Systems Fuel/Air Mixtures Backfire results from slow burning of the lean mixture If the charge is still burning when the intake valve opens, it ignites the fresh mixture and the flame travels back through the combustible mixture in the induction system 45 Engine Fuel and Fuel Metering Systems Fuel/Air Mixtures Detonation is uncontrolled burn from hot spots or high temperature lean mixture etc The Carburetor AVIA-1065 47 The Carburetor Venturi Principles The carburetor measures the airflow through the induction system uses this measurement to regulate the amount of fuel discharged into the airstream the air measuring unit is the venturi uses a basic law of physics as the velocity of a gas or liquid increases, the pressure decreases 48 The Carburetor Venturi Principles The carburetor https://www.youtube.com/watch?v=gIdXLMVP6VU https://www.youtube.com/watch?v=9BYm0HnLGRU&t=1s https://www.youtube.com/watch?v=rV0204fEb_o 49 Reciprocating Engines BREAK! RETURN AT 3 50 Carburetion Principles Venturi Principles As shown in Figure 2-4, the simple venturi is a passageway or tube in which there is a narrow portion called the throat. As the velocity of the air increases to get through the narrow portion, its pressure drops. Note that the pressure in the throat is lower than that in any other part of the venturi. This pressure drop is proportional to the velocity and is, therefore, a measure of the airflow. The basic operating principle of most carburetors depends on the differential pressure between the inlet and the venturi throat https://youtu.be/xJse_Myb1_8 51 Carburetion Principles Application of Venturi Principles to Carburetors The carburetor is mounted on the engine so that air to the cylinders passes through the barrel, the part of the carburetor which contains the venturi. The size and shape of the venturi depends on the requirements of the engine for which the carburetor is designed A carburetor for a high-powered engine may have one large venturi or several small ones The air may flow either up or down the venturi, depending on the design of the engine and the carburetor 52 Carburetion Principles Application of Venturi Principles to Carburetors Those in which the air passes downward are known as downdraft carburetors, and those in which the air passes upward are called updraft carburetors. Some carburetors are made to use a side draft or horizontal air entry into the engine induction system 53 Carburetion Principles Application of Venturi Principles to Carburetors piston moves toward the crankshaft (down) pressure in the cylinder is lowered air rushes through the carburetor and intake manifold to the cylinder airflow must pass through the carburetor venturi throttle valve is located between the venturi and the engine linkage connects this valve with the throttle lever in the cockpit airflow to the cylinders is regulated and controls the power output of the engine 54 Carburetion Principles Application of Venturi Principles to Carburetors when more air is admitted to the engine by opening of the throttle valve the carburetor automatically supplies enough additional gasoline to maintain the correct fuel/air ratio because as the volume of airflow increases the velocity in the venturi increases lowering the pressure and allowing more fuel to be forced into the airstream the throttle valve obstructs the passage of air very little when it is parallel with the flow 55  Carburetion Principles Application of Venturi Principles to Carburetors Throttle action is illustrated in Figure 2-6 Note how it restricts the airflow more and more as it rotates toward the closed position https://www.youtube.com/watch?v=9BYm0HnLGRU 56 Carburetor Systems AVIA-1065 57  Metering and Discharge of Fuel https://www.youtube.com/watc h?v=NhdIh8caqUc&list=PLhtIpSe AnaZ- m0NC72Nx195W_B2jBCsDx https://www.youtube.com/watc h?v=caPd96m8J7w&t=11s Carburetor Systems 58 Carburetor Systems Metering and Discharge of Fuel 59 Carburetor Systems Metering and Discharge of Fuel The float-operated needle valve regulates the flow through the inlet, which maintains the correct level in the fuel float chamber [Figures 2-8 and 2-9] This level must be slightly below the outlet of the discharge nozzle to prevent overflow when the engine is not running 60 Carburetor Systems Metering and Discharge of Fuel The float-operated needle valve regulates the flow through the inlet, which maintains the correct level in the fuel float chamber This level must be slightly below the outlet of the discharge nozzle to prevent overflow when the engine is not running Carburetor Systems Metering and Discharge of Fuel discharge nozzle is located in the throat of the venturi where the lowest drop in pressure occurs as air passes through the carburetor two different pressures acting on the fuel in the carburetor low pressure at the discharge nozzle higher (atmospheric) pressure in the float chamber forces the fuel through the discharge nozzle into the airstream 62 Carburetor Systems Metering and Discharge of Fuel throttle is opened wider increase the airflow to the engine greater drop in pressure at the venturi throat higher differential pressure – fuel discharge increases in proportion to the increase in airflow throttle is moved toward the “closed” position the airflow and fuel flow decrease 63 Carburetor Systems Metering and Discharge of Fuel fuel must pass through the metering jet to reach the discharge nozzle[Figure 2-7] 64 Carburetor Systems Metering and Discharge of Fuel A metering jet is a certain size hole that the fuel passes through size of this jet determines the rate of fuel discharge at each differential pressure if it was replaced with a larger one, fuel flow increases, resulting in a richer mixture If a smaller jet is installed, decrease in fuel flow and a leaner mixture would result 65 Carburetor Systems To provide for engine operation under various loads and at different engine speeds, each carburetor has six systems: 1. Main metering 2. Idling 3. Accelerating 4. Mixture control 5. Idle cutoff 6. Power enrichment or economizer Each of these systems has a definite function. It may act alone or with one or more of the others (m*i*a*m*i*p) 66 The End 67