- - AGRICULTURE CORE CURRICULUM - - (CLF2000) Advanced Core Cluster: AGRICULTURAL MECHANICS (CLF2850) Unit Title: TYPES OF ENGINES ______________________________________________________________________________ (CLF2854) Topic: ENGINE SYSTEMS Time Year(s) 8 Hours 1 / 2 / 3 / 4 ______________________________________________________________________________ Topic Objectives: Upon completion of this lesson, the student will be able to: Learning Outcome #: (R-2) - Be able to identify the major parts of an engine. (R-5) - Be familiar with the terminology used in describing carburetion systems. (R-6) - List the purpose of each component of a fuel system. (R-7) - Explain the theory of carburetion. (R-8) - Identify the components and explain the theory of an ignition system. (R-9) - Test, repair, and/or replace components of the ignition system. Special Materials and Equipment: Examples of different carburetors, samples of all parts of each system covered in the following material References: Jacobs, C. O., & Harrell, W. R. (1983). AGRICULTURAL POWER AND MACHINERY. New York: McGraw-Hill. Resources: Deere & Company. (1986). ENGINES (6th ed.) (Fundamentals of Service (FOS) Series). Available from: John Deere Technical Services, Dept. F, John Deere Road, Moline, IL 61265 (Available in German, Dutch, Swedish) Evaluation: Quiz by instructor, evaluation of lab work,student participation, and evaluation of lab on Supplemental Worksheet #4. TOPIC PRESENTATION: ENGINE SYSTEMS A. Gasoline Fuel System - Engine power and efficiency depend on correct fuel metering and distribution which is the function of the engine fuel system, mainly the carburetor. 1. Parts of a Typical Gasoline Fuel System a. Fuel Tank - normally sized to permit 8-12 hours of continuous operation of the attached engine. It may include a vent and/or screen or filter to keep fuel clean. Location of the tank should keep the fuel cool since cool fuel has more power. b. Fuel Lines - remote location of the fuel tank requires the use of steel or flexible neoprene fuel lines to carry fuel to the engine. c. Fuel Pump - provides a small amount of pressure (3 - 7 psi) to force fuel through the system and into the carburetor. The fuel pump can be either mechanical or electric. d. Fuel Filter - located either ahead of or after the fuel pump. It cleans the fuel; some fuel filters can separate out water. e. Carburetor - distributes, regulates, and meters both fuel and air into the engine which in turn controls the speed and power with which the engine operates. 2. Types of Carburetors a. Side draft - designed to draw air through the venturi in a horizontal plane. (common on motorcycles) b. Down draft - designed to draw air down through the venturi in a vertical plane. (common on automobiles) c. Up draft - designed to draw air up through the venturi in a vertical plane. (common on tractors) 3. Carburetor Designs a. Float design - regulates the level of gasoline in the metering bowl by using a float and inlet valve. A very accurate method of metering fuel for larger displacement engines. b. Diaphragm design - regulates the fuel metering on demand by only allowing the correct amount of fuel through the diaphragm inlet valve and into the venturi pickup tube. This design can be used in any position and resists faulty metering due to vibration or movement. Many two-cycle engines use this type. 4. Carburetor Theory - Carburetors operate on the principle of changes in air pressure throughout the carburetor. Starting with atmospheric pressure at 14.7 psi (sea level), the pressure within the carburetor changes according to what is demanded of the engine. This change in pressure varies the amount of air-fuel mixture that is allowed to enter into the intake manifold. a. Airfoil Effect - One of the basic parts of the carburetor and a key part of the design is the jet. The load jet usually consists of a hollow tube placed in the air flow going through the carburetor air horn; it allows the fuel to be brought to the air flow where it can be drawn out into the moving air stream. This process is accomplished by the change in air pressure around the jet or tube. b. Venturi - The second part of the carburetor responsible for movement of fuel into the airstream is the venturi. When sustained fuel metering into the engine is wanted, the placement of a smooth restriction, or narrowing down, in the carburetor air horn provides a continuous and variable low pressure area which is designed to surround the jet and meter fuel to the moving airstream. The venturi has the shape of an airplane wing in cross section and it causes a low pressure but high speed flow of air past this point. Since air and fluid move from high pressure areas to low pressure areas the fuel is drawn out the back of the tube and into the moving airstream going into the engine. After the air is past the restriction or venturi, it slows down and the normal pressure returns to this part of the airstream. c. Compensating Devices 1) Choke - designed to provide an excess of fuel to the engine for starting in cold weather 2) Idle Circuit - a passage or alternate route around the main jet to guide fuel into the engine during very low RPM's and extremely slow air movement through the air horn 3) Accelerator Pump - a device that squirts raw fuel into the airstream when the throttle butterfly is opened up in order to prevent a lean mixture from developing in the airstream B. Diesel Fuel Systems - The diesel or compression ignition engine also controls the power output and engine RPM by changes in the size of the fuel charge burned. In the diesel, however, the engine takes in only air to the combustion chamber without a restriction or a throttle butterfly to interrupt or limit the amount of air going to the engine. Consequently, the diesel is sometimes called a throttle-less engine. This lack of restriction, in addition to the accurate metering control provided by the diesel fuel system, provides overall engine economy. 1. Parts of the Diesel Fuel System a. Fuel Tank - holds enough fuel to provides a 8-12 hours of continuous engine operation; it is sually designed to trap contaminants and water. In addition to having the same features as a gasoline fuel tank, it also has a drain petcock to allow the contaminants to be eliminated. b. Fuel Lines - same as gasoline fuel system. c. Fuel Filters - usually two or more system filters designed to filter down to a 5 micron size particle diameter and also to separate out water from the fuel. The fuel filtration is much more important in a diesel engine because the fuel system parts are manufactured to sometimes millionths of an inch clearance and therefore need cleaner fuel. d. Fuel Pump - same as gasoline fuel system. e. Transfer Pump - an additional low pressure fuel pump which can provide slightly different functions depending on the design of the diesel system, but which normally controls the fuel movement through the main diesel pump. (Normal pressure = 30 - 80 psi.) f. Diesel Injection Pump - a high pressure (2000 - 3000 psi or higher) fuel pump designed to provide: 1) Fuel volume and delivery rate to the injector 2) Fuel distribution (equalization) to each cylinder 3) Fuel timing (delivery time) to each cylinder 4) Fuel pressurization to each injector 5) The timing advance which changes fuel delivery in response to changes in load g. Diesel Injector - a small spray nozzle used to force high pressure diesel fuel into the combustion chamber at the end of the compression stroke. Usually connected to the diesel pump with a high pressure fuel line. The fuel injector: 1) Atomizes the fuel into tiny droplets of fuel 2) Distributes the fuel throughout the combustion chamber 3) Provides a positive beginning and ending to the injection cycle 2. Fuel Injection System - This provides the same timing function to the Otto cycle engine as the spark does on a spark ignition engine. In addition, the fuel injection system also delivers the correct amount of fuel into the combustion chamber at this precise time. a. Types of Injection Systems 1) Direct Injection - injects fuel into the main combustion chamber above the piston 2) Indirect Injection - injects fuel into a pre-combustion chamber located adjacent to the main combustion chamber b. Types of Fuel Injection Pumps 1) Inline or "jerk" pumps utilize a plunger and a barrel which operate in a reciprocating motion to trap diesel fuel and send it to the injector at high pressure. 2) Rotary pumps are distributor-type pumps which utilize a cam ring to drive two plungers together creating high pressure fuel and sending it to the injector. c. Types of Injector Nozzles 1) Unit Injector - an inward-opening combination pump and injector in one housing, used by Detroit diesel engines 2) Pencil Injector - a small, slender, inward-opening nozzle used with either inline or rotary injector pumps 3) Injection Nozzle - a larger injector which can be either an inward-opening, outward-opening, or accumulator-type nozzle normally used with inline pumps 1 2 3 +..... +..... +..... Injectors ----> | : | : | : | : | : | : : : : <----Fuel lines, equal : : : length ....: : : | ........: : | | ...........: _ |^|__|^|__|^|_ | ____________ | _---_ _| |____________| | <----- Injection pump, inline, _|-| _ _ _ _| three cylinder |-|_ |_| |_| |_| | |__________________| Firing Order = 1, 2, 3 C. Air Intake System 1. The air intake system on an engine is a very important part of the engine. Air is the key to a good combustion process and yet the most difficult to get into the engine. For each gallon of fuel burned, the engine must have 9,000 to 10,000 gallons of air. The intake system is critical to the life of the engine since the close fitting parts must be lubricated and any dirt that gets past the filter unit causes the engine to wear very fast. 2. Parts of the Air Intake System a. Precleaner - a unit designed to take out larger particles of dirt and trash. It is installed just in front of the air cleaner and can remove as much as 90% of the dirt from the air. b. Air Cleaner - a wet or dry type element which is the final stage of filtering before the engine receives the cleaned air. c. Inlet Hoses - all connections and ducts which conduct the incoming air to the engine are potential leaks which should be checked and secured from dirt infiltration. d. Intake Manifold - a unit designed to conduct the moving air mass to the combustion chamber with the least air restriction. It may also include a warming device for easier starting of diesel engines or it may be used to cool the incoming air if it is designed as an intercooler following a turbocharger. e. Service Indicator - either a mechanical or an electrical unit which senses any restriction to the incoming air and notifies the operator of service needed. 3. Air Cleaner Types a. Pre-cleaner - normally placed high above the engine or in a clean air portion of the engine compartment. It is a simple screen device (pre-screener) designed to centrifuge the incoming air mass to separate out the heavier dirt particles from the lighter clean air. /-----------------\ DIRTY AIR----> | | C | | <----DIRTY AIR |------| L |------| | E | PRE-CLEANER ELEMENT | A | | N | | | ______________________| A |_____ CLEAN | ......................I..... | AIR _______| ::::::::::::::::::::: R :::: | <------_______ :::::FILTER ELEMENT::::::::: |+ TO | :::::::::::::::::::::::::::: | DIRT ENGINE |______________________________| UNLOADING |___| <------ VALVE b. Dry Element Cleaner - The dry element cleaner is composed of a pleated paper element of special paper sized to filter out particles that pass through the pre-cleaner. Many of these elements also include a backup safety element in the event that the primary element fails. c. Viscous-impingement Cleaner - The air flows through a dense core of metal or wire wool which is saturated with oil to trap the dirt particles as they pass through. d. Spiral Rotor Cleaner - This type utilizes a vacuum created by a venturi attached to the muffler. The vacuum is directed to a series of spiral rotor tubes which incoming air passes through. As the air is spun through the tubes, the heavy dirt particles are thrown to the outside and drawn off by the vacuum action. This type is usually used in conjunction with the dry element type filter. e. Oil Bath Cleaner - One of the oldest style air filters uses the sticky quality of oil to trap the dirt as the air rushes through the element. In addition to the oil, this type of air cleaner is designed to make the direction of the air going through the element alter course so the heavier dirt particles are trapped in the oil bath. This happens because the air can change its direction faster than the particles of dirt. D. Valve System - a series of poppet-type valves which control the air movement through the engine. (On a ported 2-cycle engine, the piston acts as a sliding-type valve to provide the same function.) 1. Timing Gears - connected to the crankshaft and drives the valve train at 1/2 engine speed (4-cycle engine) or at crankshaft speed (2-cycle engine) to open and close the poppet valves during each Otto cycle. 2. Camshaft - a shaft passing through the engine which lifts the valve tappets due to its eccentric shape; it is driven by the timing gears. 3. Valve Tappet - a metal cylinder which rides on the camshaft and absorbs side loads and wear created by the camshaft. 4. Push Rod - used with an overhead valve engine to accept and transmit camshaft lift to the rocker arm above the head. 5. Rocker Arm - transmits the movement of the push rod to the end of the intake or exhaust valve to open and close these valves. 6. Valve Springs - close and hold the valves in the closed position to seal the combustion chamber during the power and compression strokes of the Otto cycle. 7. Valves (Intake and Exhaust) - control the movement of air or air/fuel into and out of the combustion chamber and to seal the cylinder pressures. Head.... _________ \__ __/......Face | | | | Stem.....| | | | POPPET-TYPE VALVE | | |*| |_| E. Exhaust System 1. The function of the exhaust system is to carry away the burned exhaust gases, muffle the engine noise, and eliminate engine heat. 2. Parts of the Exhaust System a. Exhaust Manifold - receive and collect the burned gases from the combustion chamber. In gasoline engines, some of the heat is used to maintain a pre-heated intake manifold to assist in vaporizing the gasoline. b. Muffler - works to quiet the exhaust noise and cool the gases; it may include a venturi unit to assist in cleaning the incoming air at the air cleaner. c. Exhaust Pipe - carries away the burned gases and can direct the exhaust away from the operator while protecting the engine from rain and cold air entering through the exhaust. A flapper valve at the end of a vertical exhaust pipe is called a rain cap. d. Spark Arrester - for prevention of wildfire and to meet fire codes. F. Turbocharger 1. The turbocharger is an exhaust-driven turbine which powers a small centrifugal compressor wheel designed to increase the incoming air pressure fed to the engine. The exhaust turbine (hot wheel) makes use of the still-expanding hot exhaust gases to spin the compressor (cold wheel) which forces more air into the cylinder. The power increase comes because with more air a greater amount of fuel is burned and this produces more power. The turbocharger is also used to help maintain sea level atmospheric pressure at high altitudes when the engine would otherwise lose much of its power. 2. Parts of the Turbocharger a. Turbine Housing - outer mounting unit which supports the turbine shaft and bearings as well as the exhaust and inlet housings. b. Exhaust Turbine Wheel - receives the hot gases and spins which absorbs energy and cools the exhaust gas. Some turbines spin at up to 150,000 RPM. c. Compressor Wheel - acts as a fan to force air into the engine which also heats the air as it is being compressed. Air temperatures can increase by as much as 50 or more degrees Fahrenheit. d. Compressor Shaft & Bearings - the shaft unit spins on a set of oil bushings which allows a very high turbine speed to develop (100,000 - 150,000 RPM). e. Seals - at both ends of the shaft are seals which separate the oil around the shaft from the exhaust housing or the inlet housing. Each end has a special design so they are not interchangeable. 3. Turbocharger Design a. Size - depends on the cubic inch displacement of the engine and desired performance of the turbocharger b. Waste Gate - the turbocharger is designed to turn faster as engine speed increases. This works well up to a point where the boost pressure exceeds the design limits. In order to maintain a constant boost pressure of from 2 - 8 psi, a waste gate valve is installed in the exhaust system at the turbo; this diverts the exhaust around the turbine and thus limits the maximum boost available to the engine. c. RPM - revolutions per minute; various RPM's are used in developing the turbine flow. Most large engine applications, trucks, and buses can use large, slow-spinning turbine wheels. The reaction time necessary for the turbocharged air to reach the cylinder is slower. With smaller engines in automobiles or when there is a great deal of rapid acceleration and deceleration, a small, lightweight turbine wheel is needed so it can change the air flow more rapidly. 1) Large engine RPM ranges from 60,000 to 100,000 2) Small engine RPM ranges from 100,000 to 150,000 G. Lubricating System l. The purpose of the lubricating system is to provide lubricating oil to moving engine components. 2. Components of the Lubricating System a. The oil pump pushes oil through the system. b. The crankcase serves as a reservoir for engine oil. c. The oil filter removes dirt and other extraneous material from the crankcase oil. The oil filter should be replaced regularly to avoid blockages and oil circulation problems. d. The entire engine is filled with oil passages which deliver oil (as a lubricant) to and from the moving engine parts. e. The pressure regulating valve and gauge changes and indicates the pressure on the oil pump. The gauge is generally located on the dashboard to warn the driver of significant changes in oil pressure. The regulating valve can automatically relieve some of the oil pressure as it begins to build. H. Cooling System l. The cooling system prevents overheating of the engine and helps to regulate the engine temperature. 2. Cooling System Components a. Radiator and Liquid Coolant 1) The radiator provides storage for coolant and allows air flow through its core to remove heat from the coolant. 2) The coolant conveys heat from engine to radiator where heat is dissipated. The coolant is a mixture of antifreeze and water. a) Antifreeze (normally ethylene glycol) raises the boiling point and lowers the freezing point of the coolant. Antifreeze also contains lubricating agents for the coolant passages and contains anti- rust ingredients which prolong the life of the cooling system components. b. The radiator pressure cap regulates the cooling system pressure (i.e., the boiling point) and enables the escape of coolant or steam when a certain pressure is reached. c. The fan and fan belt function to push or pull air through the radiator to remove heat from the coolant. d. The water pump circulates coolant through the engine and radiator allowing more effective removal of heat from the coolant. e. The thermostat allows engine coolant to warm quickly by not allowing coolant to travel to the radiator until a certain coolant temperature is reached. As the coolant temperature increases, the thermostat opens to allow circulation of the coolant throughout the system. f. Connecting hoses connect the radiator to the engine block. These hoses and their connections must be checked regularly to prevent leaks in the cooling system. I. Electrical System 1. The electrical system provides charging and starting for all engines and an ignition spark in gasoline engines. Each function of the electrical system--charging, starting, and ignition--is a separate sub-system in itself and each has specific functions. 2. The charging system recharges the battery and generates power during engine operation for engine and accessory (for example, lights demand. a. Components of the Charging System l) The battery provides power to start the engine and, at times, to run accessories. 2) The voltage regulator regulates the voltage and current output of the generator, or alternator, preventing damage to the battery or other circuits. 3) Alternator or Generator a) The generator produces DC power (mechanically rectified from AC) which is used to recharge the battery and/or provide power for other engine and vehicle electrical needs. b) The alternator produces DC power (electronically rectified from AC) which is used to recharge the battery and/or provide power for other engine and vehicle electrical needs. 3. The starting circuit provides electrical energy from the battery to the starting motor in order to crank the engine to start. a. Components of the Starting System l) The battery is the initial component in the starting system as it is in the charging system. The battery provides an electrical charge to the starting motor in order to crank the engine. 2) The starter switch closes the circuit in order to activate the starting circuit. 3) The motor switch (solenoid) completes the electrical circuit to enable the starting motor to turn. 4) The starting motor engages and turns the engine flywheel to start the engine. 4. The ignition system (gasoline engines only) creates a high voltage spark which is synchronized with other components to ignite the air-fuel mixture in the engine cylinder. a. Components of the Ignition System l) The ignition coil transforms the low battery voltage (6 or 12 volts) into a high energy spark at the spark plug (20,000 volts or more). 2) The distributor times the high voltage spark produced by the coil and directs the voltage to the proper spark plug at the proper time. 3) The spark plug and coil wires deliver electricity between either the distributor and coil (coil wire) or the distributor and spark plugs (spark plug wires). 4) The spark plugs receive the voltage surge and provide a gap for the spark to "jump across" and ignite the air- fuel mixture. 5) The function of the ignition switch is to provide a complete electrical circuit which enables all of the ignition functions to occur. The circuit is completed when the driver turns the key. b. Ignition System Testing 1) The VOA meter (Volt, Ohm, Amp.) is used for low voltage testing. The VOA meter is especially useful to isolate electrical shorts and other problems in the primary ignition circuit. 2) Voltage is checked in parallel in the circuit by jumping across from the hot wire to any good ground. The reading is taken directly from the VOA meter. 3) Amperage is checked by connecting the ammeter in series in the circuit which means ALL the current must flow through the meter. The reading is taken directly from the meter. 4) Ohms or resistance in a connection or wire is also checked in series to determine if all the current can or is flowing in the wire. This is referred to as continuity. 5) A simple continuity meter or test light for low voltage current can be purchased or made using a small light bulb and two short wires, one soldered to the base and the other to the insulated point on the bulb. c. Spark Plug Testing 1) Testing the spark plug is normally done by grounding the base and applying a high voltage (20,000 volts) to the insulated end of the terminal. 2) Although the above test will work, it does not show how the plug functions under compression pressure. Some small spark plug testers are available which also use compressed air to simulate the compressed atmosphere. These are a more reliable test of spark plugs. 3) The use of abrasive blasters to clean spark plugs is generally NOT recommended because the abrasive material is difficult to totally clean out of the spark plug; it can quickly ruin an engine. d. Secondary Ignition Testing 1) Testing of the secondary ignition system is usually done first because it also tests an important part of the system. 2) The quickest test for spark at the secondary ignition system is to remove the spark plug and hold the lead (wire) about 1/8 inch away from a good ground; a crisp, blue electric spark should jump the gap between the wire and the ground. 3) A small, high voltage tester, used mostly with small engines, is also available which is calibrated to give a more reliable visual test of secondary spark. e. Primary Ignition Testing 1) The primary system is the low voltage system and as such can be shorted out very easily. This system is usually tested by putting a low voltage current through the system and using a VOA meter to check for circuit continuity. This must be done with the points closed. 2) Another test is to open the points with the circuit "hot" or key on, and visually check for a small spark between the points. 3) The most common part failures in the ignition system are the ignition points and the condenser. They will arc and burn (out rapidly) when a short occurs. Because of this, the points and condenser are usually replaced as a set. f. MOST PROBLEMS (90%) IN SPARK IGNITION ENGINES ARE ELECTRICAL OR INVOLVE THE ELECTRICAL SYSTEM. J. Power Train Parts - those parts which accept pressure and force and produce or transmit motion to the flywheel. 1. Piston - receives expanding gas pressure and creates the force necessary to produce horsepower 2. Piston Pin - connects piston to connecting rod and allows the piston to pivot on the small end of the connecting rod 3. Connecting Rod - transmits the reciprocating motion of the piston to the rotary motion of the crankshaft and forces the piston back up to the top of the stroke 4. Crankshaft - receives the reciprocating motion from the large end of the connecting rod and converts it to a rotary force called torque at the flywheel 5. Flywheel - stores the energy produced by the piston via centrifugal force and smooths out the Otto cycle, especially in a four-stroke cycle engine; also provides: a. Cooling fins for many air cooled engines b. Starter adaption and power-take-off points __________________________________________________________ ACTIVITY: 1. Lay out the component parts in the correct order from fuel tank to carburetor or injector nozzle. 2. Provide each student with the Supplemental Worksheet #4. 3. Have students "pop test" an injector to determine the pressure, identify leakage, and diagram the injection pattern. 4. Service each type of air cleaner using the correct service procedures. 5. Have students develop a parts quiz to give to each other which shows the interrelation of the different engine systems. 6. Have students develop flow diagrams for each of the engine systems; all components of each system should be included in the proper place and spelled correctly. __________________________________________________________ SUPPLEMENTAL WORKSHEET #4 FUEL SYSTEMS NAME _____________________________________ DATE _____________________________________ CLASS _____________________________________ A. Identify each of the displayed carburetor parts by its complete, correct name: 1. ___________________________________ 2. ___________________________________ 3. ___________________________________ B. Diagram a complete diesel fuel system from tank to injector; show all individual components and label each part. C. Use the diesel injection nozzle tester and "pop test" one nozzle to determine the "pop off" pressure. Then readjust the pressure by decreasing the setting 200 psi and retest the nozzle. Test Pressure Before __________________. Test Pressure After __________________. NOTE: USE CAUTION WHEN TESTING NOZZLES - DIESEL FUEL CAN CASE BLOOD POISONING IF INJECTED THROUGH THE SKIN. 7/15/91 YNJ/tf #%&c