Lesson 4 Reciprocating Engine Design and Construction Reciprocating

Lesson 4: Reciprocating Engine Design and Construction

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

Reciprocating Engine Design and Construction • Crankcase • Foundation of the engine, containing the bearings in which the crankshaft revolves.

Reciprocating Engine Design and Construction • 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.

Reciprocating Engine Design and Construction • Opposed Engine Crankcase Bearings

Reciprocating Engine Design and Construction • Crankshafts • Transforms the reciprocating motion of the piston and connecting rod into rotary motion for the propeller.

Reciprocating Engine Design and Construction • Crankshaft • Backbone of engine. • Forged from very strong alloy (Chromiumnickel-molybdenum steel). • Single or multi-piece.

Reciprocating Engine Design and Construction • Crankshaft • Four-throw used on four-cylinder engines. • Six-throw used on six-cylinder engines. • Three Main Parts – Journal – Crankpin – Crankcheek

Reciprocating Engine Design and Construction • Crankshaft Balance • Dynamic dampers are used to reduce vibration during engine operation. • Pendulum which is fastened to the crankshaft.

Reciprocating Engine Design and Construction • Connecting Rods • Link which transmits forces between the piston and the crankshaft. Master and Articulated Fork and Blade Plain

Reciprocating Engine Design and Construction • 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.

Reciprocating Engine Design and Construction • Fork And Blade Assembly • Used primarily in V-type engines.

Reciprocating Engine Design and Construction • Plain Type Connecting Rod • Used in in-line and opposed engines.

Reciprocating Engine Design and Construction • Pistons • Acts as a moving wall within the combustion chamber.

Reciprocating Engine Design and Construction • 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.

Reciprocating Engine Design and Construction • 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.

Reciprocating Engine Design and Construction • Piston Types • Trunk Type • Slipper Type – Not used in aircraft Slipper Trunk

Reciprocating Engine Design and Construction • Piston Rings • Compression Rings • Oil Control Rings • Oil Scraper Rings Pin boss

Reciprocating Engine Design and Construction • 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

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

Reciprocating Engine Design and Construction • 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.

Reciprocating Engine Design and Construction • 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.

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

Reciprocating Engine Design and Construction • 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 for cooling.

Reciprocating Engine Design and Construction • 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 renitrided or chrome plated. • Chrome plated cylinders can be recognized by orange paint mark on cylinder.

Reciprocating Engine Design and Construction • Cylinder Numbering (Opposed Engine) • Propeller (Front) • Accessory (Rear) • Left, right (Pilot’s view)

Reciprocating Engine Design and Construction • Cylinder Numbering (Opposed Engine) • Numbering is by no means standard. • Continental starts from rear. • Lycoming starts from front.

Reciprocating Engine Design and Construction • Cylinder Numbering (Radial Engine)

Reciprocating Engine Design and Construction • 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.

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

Reciprocating Engine Design and Construction • Firing Order Single-Row-Radial • First all odd numbered cylinders fire in numerical succession. • Then the even-numbered cylinders fire in numerical succession. 1 -3 -5 -7 -9 -2 -4 -6 -8

Reciprocating Engine Design and Construction • 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.

Reciprocating Engine Design and Construction • 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.

Reciprocating Engine Design and Construction • Firing Order Opposed Engine 1 -4 -2 -3

Reciprocating Engine Design and Construction Valves

Reciprocating Engine Design and Construction • 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.

Reciprocating Engine Design and Construction

Reciprocating Engine Design and Construction • 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 cobaltchromium alloys.

Reciprocating Engine Design and Construction • Valve Construction Tip Stem Neck Face Head

Reciprocating Engine Design and 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).

Reciprocating Engine Design and 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.

Reciprocating Engine Design and Construction • 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.

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

Reciprocating Engine Design and Construction • 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 valveoperating mechanism.

Reciprocating Engine Design and Construction • 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.

Reciprocating Engine Design and Construction • Valve-Operating Mechanism (Opposed engine)

Reciprocating Engine Design and Construction • Valve-Operating Mechanism (Radial engine)

Reciprocating Engine Design and Construction • Camshaft • Valve-operating mechanism is operated by a camshaft.

Reciprocating Engine Design and Construction • Camshaft • The camshaft is driven by a gear that mates with another gear attached to the crankshaft.

Reciprocating Engine Design and Construction • 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.

Reciprocating Engine Design and Construction • Tappet Assembly

Reciprocating Engine Design and Construction • 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.

Reciprocating Engine Design and Construction • Hydraulic Valve Tappets PUSH ROD SOCKET HIGH PRESSURE OIL SOURCE

Reciprocating Engine Design and Construction • 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.

Reciprocating Engine Design and Construction • Rocker Arms • Transmits the lifting force from the cam to the valve.

Reciprocating Engine Design and Construction • Valve Springs • Function is to close the valve and to hold the valve securely on the valve seat.

Reciprocating Engine Design and Construction • 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.

Reciprocating Engine Design and Construction • Bearings

Reciprocating Engine Design and Construction • 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.

Reciprocating Engine Design and Construction • 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.

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

Reciprocating Engine Design and Construction • 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.

Reciprocating Engine Design and Construction • 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.

Reciprocating Engine Design and Construction • 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

Reciprocating Engine Design and Construction Spur and Pinion Spur Planetary

Reciprocating Engine Design and Construction • Propeller Shafts Taper Flange Spline