Lesson 4: Reciprocating Engine Design and Construction

Name: Lesson 4: Reciprocating Engine Design and Construction
Uploaded: 2017-06-29T13:47:31+00:00
Duration: PTM16S42
Channel: Edmund Briggs
Description: Lesson 4: Reciprocating Engine Design and Construction

Lesson 4: Reciprocating Engine Design and Construction

Reciprocating Engine Design and Construction
Basic Parts Crankcase Cylinders Pistons Connecting rods Valves Valve-operating mechanism Crankshaft Head Spark plugs

Crankcase Foundation of the engine, containing the bearings in which the crankshaft revolves.

Crankcase Tight enclosure for lubricating oil. Support for attachment of the cylinders and the powerplant to the aircraft. Must be rigid, strong and light. Cast of forged aluminum alloy.

Opposed Engine Crankcase Bearings

Crankshafts Transforms the reciprocating motion of the piston and connecting rod into rotary motion for the propeller.

Crankshaft Backbone of engine. Forged from very strong alloy (Chromium-nickel-molybdenum steel). Single or multi-piece.

Crankshaft Four-throw used on four-cylinder engines. Six-throw used on six-cylinder engines. Three Main Parts Journal Crankpin Crankcheek

Crankshaft Balance Dynamic dampers are used to reduce vibration during engine operation. Pendulum which is fastened to the crankshaft.

Connecting Rods Link which transmits forces between the piston and the crankshaft. Master and Articulated Fork and Blade Plain

Master and Articulated Rod Assembly Commonly used in radial engines. One piston in each row is connected to the master rod. Others are connected to the master rod by articulated rods.

Fork And Blade Assembly Used primarily in V-type engines.

Plain Type Connecting Rod Used in in-line and opposed engines.

Pistons Acts as a moving wall within the combustion chamber.

As the piston moves down it draws in fuel/air mixture. As it moves up it compresses the charge. Ignition occurs, and expanding gases force the piston down. This force is transmitted to crankshaft through connecting rod. On the return upward stroke, the piston forces the exhaust gas out.

Piston Construction Machined from aluminum alloy forgings. Grooves machined for piston rings. Cooling fins inside for greater heat transfer. Piston pin (wrist pin) joins the piston to the connecting rod.

Piston Types Trunk Type Slipper Type Not used in aircraft Slipper Trunk

Piston Rings Compression Rings Oil Control Rings Oil Scraper Rings Rings Pin boss

Compression Rings Prevent the escape of gas past the piston during engine operation. Number used depends on engine design. Cross section of the ring is either rectangular or wedge shaped

Oil Control Rings Placed in grooves immediately below the compression rings. One or more rings per piston. Regulate the thickness of the oil film on the cylinder wall.

Oil Scraper Ring Installed in the groove at the bottom of the piston skirt. Installed with the scraping edge away from the piston head or in the reverse position. Returns surplus oil to the crankcase.

Cylinders The portion of the engine in which the power is developed. Provides a combustion chamber where the burning and expansion of gases take place. Houses the piston and the connecting rod.

Cylinders Either produced singly or cast in a block. Air-cooled engine uses the overhead valve type. Two major parts: Head, Barrel.

Cylinder Heads Provides a place for combustion of the fuel/air mixture. Gives the cylinder more heat conductivity for cooling. Contains the intake valve, exhaust valve and sparkplugs. Contains fins for cooling.

Cylinder Barrels Made of a steel alloy forging with the inner surface hardened to resist wear. (Nitrided) Worn Cylinder walls can be ground out and re-nitrided or chrome plated. Chrome plated cylinders can be recognized by orange paint mark on cylinder.

Cylinder Numbering (Opposed Engine) Propeller (Front) Accessory (Rear) Left, right (Pilot’s view)

Cylinder Numbering (Opposed Engine) Numbering is by no means standard. Continental starts from rear. Lycoming starts from front.

Cylinder Numbering (Radial Engine)

Cylinder Numbering (Radial Engine) Numbered clockwise as viewed from the accessory end. Single-row, cylinder No. 1 is the top cylinder. Double-row, all odd-numbered cylinders are in the rear, and all even numbered cylinders are in the front.

Firing Order The Sequence in which the power event occurs in the different cylinders. Designed to provide for balance and to eliminate vibration.

Firing Order Single-Row-Radial First all odd numbered cylinders fire in numerical succession. Then the even-numbered cylinders fire in numerical succession.

Firing Order Double-Row-Radial Arranged with the firing impulse occurring in a cylinder in one row and then in a cylinder in the other row. Two cylinders in the same row never fire in succession.

Firing Order Opposed Engine Lycoming and Continental number their cylinders differently which gives us two sets of firing orders. But the firing impulses are the same.

Firing Order Opposed Engine

Valves

Valves Fuel/air mixture enters the cylinders through the intake valve. Burned gases are expelled through the exhaust valve. Mushroom or tulip type depending on shape.

Valve Construction Intake valves, because of lower operating temperatures, can be made of chrome-nickel steel. Exhaust valves are made of exotic metals such as inconel, silicon-chromium or cobalt-chromium alloys.

Valve Construction Head Face Neck Tip Stem

Valve Construction Valve head has ground face which forms a seal against the ground valve seat in the cylinder head. Valve face ground to an angle of either 30° or 45°. Valve face made more durable by the application of stellite (an alloy of cobalt and chromium).

Valve Construction Valve stem acts as a pilot for the valve head and rides in the valve guide. Surface-hardened to resist wear. Some stems are hollow and partially filled with metallic sodium.

Valve Construction The neck is the part that forms the junction between the head and the stem. The tip is hardened to with stand the hammering of the valve rocker arm.

Valve Construction Machined groove near tip receives the split-ring keys which form a lock ring to hold the valve spring retaining washer.

Valve-Operating Mechanism Each valve must open at the proper time, stay open for the required length of time, and close at the proper time. Timing of the valves is controlled by the valve-operating mechanism.

Valve-Operating Mechanism Intake valves open just before the piston reaches top dead center, and exhaust valves remain open after top dead center. At this particular instant both valves are open at the same time (end of the exhaust stroke and beginning of the intake stroke). This valve overlap results in better volumetric efficiency and lower operating temperatures.

Valve-Operating Mechanism (Opposed engine)

Valve-Operating Mechanism (Radial engine)

Camshaft Valve-operating mechanism is operated by a camshaft.

Camshaft The camshaft is driven by a gear that mates with another gear attached to the crankshaft.

Tappet Assembly Converts rotational movement of the cam lobe into reciprocating motion. Transmits this motion to the push rod, rocker arm, and then to the valve tip. Opening the valve at the proper time.

Tappet Assembly

Hydraulic Valve Tappets Designed to automatically keep the valve clearance at zero. Ball check valve traps oil in the pressure chamber and. Acts as a cushion as the camshaft rotates.

Hydraulic Valve Tappets PUSH ROD SOCKET HIGH PRESSURE OIL SOURCE

Push Rod Transmits the force from the valve tappet to the rocker arm. Tubular form used because of its strength Permits lubricating oil to pass through the hollow rod to the ball ends.

Rocker Arms Transmits the lifting force from the cam to the valve.

Valve Springs Function is to close the valve and to hold the valve securely on the valve seat.

Valve Springs Two or more springs used to eliminate spring vibration or surging during different engine speeds. Held in place by split locks installed in the recess of the valve spring upper retainer washer.

Bearings

Bearings Any surface which supports, or is supported by, another surface. Composed of material that is strong enough to withstand the pressure imposed on it. Permit the other surface to move with a minimum of friction and wear. Lubricated bearings.

Bearings Three types of lubricated bearings used: Plain Bearings Ball Bearings Roller Bearings Bearings are required to take radial loads, thrust loads, and a combination of the two.

Plain Bearings Used for crankshaft, cam ring, camshaft, connecting rods, and accessory drive shaft. Subjected to radial loads. Made of nonferrous metals.

Ball Bearings Used in supercharger impeller shaft bearings and rocker arm bearings. Special deep groove ball bearings are used in some aircraft engines to transmit propeller thrust to the engines nose section.

Roller Bearings Straight roller bearings used where the bearing is subjected to radial loads only. Tapered roller bearings used where bearing is subjected to both radial and thrust loads.

Propeller Reduction Gearing Turns the propeller at a slower speed than the engine. Increases propeller efficiency. Three types: Spur Planetary Bevel Planetary Spur and Pinion

Spur and Pinion Spur Planetary

Propeller Shafts Spline Taper Flange

Lesson 4: Reciprocating Engine Design and Construction

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Lesson 4: Reciprocating Engine Design and Construction

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