Halderman ch018 lecture

GASOLINE ENGINE OPERATION, PARTS, AND SPECIFICATIONS 18

Objectives The student should be able to: Prepare for Engine Repair (A1) ASE certification test content area “A” (General Engine Diagnosis). Explain how a four-stroke cycle gasoline engine operates. List the various characteristics by which vehicle engines are classified.

Objectives The student should be able to: Discuss how a compression ratio is calculated. Explain how engine size is determined. Describe how displacement is affected by the bore and stroke of the engine.

Purpose and Function Convert heat energy of burning fuel into mechanical energy Mechanical energy is used to perform the following: Propel the vehicle

Purpose and Function Mechanical energy is used to perform the following: Power the air-conditioning system and power steering Produce electrical power for use throughout the vehicle

Energy and Power Engines use energy to produce power Combustion: fuel is burned at a controlled rate to convert chemical energy to heat energy

Energy and Power Combustion occurs within the power chamber in an internal combustion engine Engines in automobiles are internal combustion heat engines

Energy and Power NOTE: An external combustion engine burns fuel outside of the engine itself, such as a steam engine.

Engine Construction Overview Block Solid frame from which all automotive and truck engines are constructed Constructed of cast iron or aluminum

Engine Construction Overview Rotating Assembly Constructed of pistons, connecting rods and a crankshaft

Figure 18-1 The rotating assembly for a V-8 engine that has eight pistons and connecting rods and one crankshaft.

Engine Construction Overview Cylinder Heads Seal top of cylinders in the engine block Contain both intake valves and exhaust valves Constructed of cast iron or aluminum ?

Figure 18-2 A cylinder head with four valves per cylinder, two intake valves (larger) and two exhaust valves (smaller).

Engine Parts and Systems Intake and Exhaust Manifolds Air and fuel enter and exit the engine through manifolds Intake manifolds are constructed of nylon-reinforced plastic or aluminum

Engine Parts and Systems Intake and Exhaust Manifolds Exhaust manifolds must withstand hot gases and are constructed of cast iron or steel tubing

Engine Parts and Systems Cooling System Controls engine temperature Vehicles are cooled by circulating antifreeze coolant

Engine Parts and Systems Cooling System Coolant picks up heat and releases it through radiator

Figure 18-3 The coolant temperature is controlled by the thermostat, which opens and allows coolant to flow to the radiator when the temperature reaches the rating temperature of the thermostat.

Engine Parts and Systems Lubrication System Oil is pumped from oil pan through oil filter, then into oil galleries to lubricate engine parts

Figure 18-4 A typical lubrication system, showing the oil pan, oil pump, oil filter, and oil passages.

Engine Parts and Systems Fuel System and Ignition System Fuel system includes the following components: Fuel tank – stores fuel and contains most fuel pumps

Engine Parts and Systems Fuel System and Ignition System Fuel system includes the following components: Fuel filter and lines - transfer fuel for the fuel tank to the engine

Engine Parts and Systems Fuel System and Ignition System Fuel system includes the following components: Fuel injectors - spray fuel into intake manifold or directly into the cylinder

Engine Parts and Systems Fuel System and Ignition System Ignition system includes the following components: Spark plugs - provide an air gap inside the cylinder where a spark occurs to start combustion

Engine Parts and Systems Fuel System and Ignition System Ignition system includes the following components: Sensor(s) - includes crankshaft position (CKP) and camshaft position (CMP)

Engine Parts and Systems Fuel System and Ignition System Ignition system includes the following components: Ignition coils - increase battery voltage to 5,000 to 40,000 volts

Engine Parts and Systems Fuel System and Ignition System Ignition system includes the following components: Ignition control module (ICM) - controls when the spark plug fires

Engine Parts and Systems Fuel System and Ignition System Ignition system includes the following components: Associated wiring - electrically connects the battery, ICM, coil, and spark plugs

Four-Stroke Cycle Operation Principles First four-stroke cycle engine developed by Nickolaus Otto in 1876 The process begins with the starter motor rotating the engine until combustion takes place

Four-Stroke Cycle Operation Principles The cycle is repeated for each cylinder of the engine Piston is attached to crankshaft with a connecting rod allowing the piston to move up and down

Figure 18-5 The downward movement of the piston draws the air-fuel mixture into the cylinder through the intake valve on the intake stroke. On the compression stroke, the mixture is compressed by the upward movement of the piston with both valves closed. Ignition occurs at the beginning of the power stroke, and combustion drives the piston downward to produce power. On the exhaust stroke, the upward-moving piston forces the burned gases out the open exhaust valve.

Figure 18-6 Cutaway of an engine showing the cylinder, piston, connecting rod, and crankshaft.

Four-Stroke Cycle Operation Operation Engine cycles are identified by the number of piston strokes required to complete the cycle

Four-Stroke Cycle Operation Operation Piston stroke: one-way piston movement Most engines use a four-stroke cycle

Four-Stroke Cycle Operation Operation Most engines use a four-stroke cycle Intake stroke Compression stroke

Four-Stroke Cycle Operation Operation Most engines use a four-stroke cycle Power stroke Exhaust stroke

Four-Stroke Cycle Operation The 720-Degree Cycle In each cycle, the engine crankshaft makes two complete revolutions (or 720 degrees)

Four-Stroke Cycle Operation The 720-Degree Cycle To find the angle between cylinders of an engine, divide the number of cylinders into 720 degrees

ENGINE CLASSIFICATION AND CONSTRUCTION

Engine Classification and Construction Engines are classified by several characteristics including: Number of strokes Cylinder arrangement

Engine Classification and Construction Engines are classified by several characteristics including: Longitudinal and transverse mounting Valve and camshaft number and location

Engine Classification and Construction Engines are classified by several characteristics including: Type of fuel Cooling method Type of induction pressure

Engine Classification and Construction NOTE: Although it might be possible to mount an engine in different vehicles both longitudinally and transversely, the engine component parts may not be interchangeable. Differences can include different engine blocks and crankshafts, as well as different water pumps. ?

Figure 18-7 Automotive engine cylinder arrangements.

Figure 18-8 A horizontally opposed engine design helps to lower the vehicle’s center of gravity.

Figure 18-9 A longitudinally mounted engine drives the rear wheels through a transmission, driveshaft, and differential assembly.

Figure 18-10 Two types of front-engine, front-wheel drive mountings.

Engine Classification and Construction Push rod engine: camshaft is located in the block, the valves are operated by lifters, pushrods, and rocker arms Push rod engine also called cam-in-block design and overhead valve (OHV)

Engine Classification and Construction Single overhead camshaft (SOHC) design uses one overhead camshaft Double overhead camshaft (DOHC) design uses two overhead camshafts

Engine Classification and Construction NOTE: A V-type engine uses two banks or rows of cylinders. An SOHC design, therefore, uses two camshafts but only one camshaft per bank (row) of cylinders. A DOHC V-6, therefore, has four camshafts, two for each bank. ?

Figure 18-11 Cutaway of an overhead valve (OHV) V-8 engine showing the lifters, pushrods, roller rocker arms, and valves.

Figure 18-12 SOHC engines usually require additional components, such as a rocker arm, to operate all of the valves. DOHC engines often operate the valves directly.

Figure 18-13 A DOHC engine uses a camshaft for the intake valves and a separate camshaft for the exhaust valves in each cylinder head.

Figure 18-14 A rotary engine operates on the four-stroke cycle but uses a rotor instead of a piston and crankshaft to achieve intake, compression, power, and exhaust stroke.

Engine Classification and Construction Engine Rotation Direction SAE standard for automotive engine rotation is counterclockwise (CCW)

Engine Classification and Construction Engine Rotation Direction Direction is viewed from the flywheel end (principal end) of the engine (end to which power is applied to drive vehicle)

Engine Classification and Construction Engine Rotation Direction Non-principal end is referred to as the front end and is opposite the flywheel end

Figure 18-15 Inline 4-cylinder engine showing principal and nonprincipal ends. Normal direction of rotation is clockwise (CW) as viewed from the front or accessory belt (nonprincipal) end.

Engine Measurement Bore The diameter of a cylinder Pressure measured in units, such as pounds per square inch (PSI)

Figure 18-16 The bore and stroke of pistons are used to calculate an engine’s displacement.

Engine Measurement Stroke Distance the piston travels from top dead center (TDC) to bottom dead center (BDC)

Engine Measurement Stroke Determined by the throw of the crankshaft The throw is the distance from the centerline of the crankshaft to the centerline of the crankshaft rod journal

Engine Measurement Stroke The throw is one-half of the stroke

Engine Measurement NOTE: Changing the connecting rod length does not change the stroke of an engine. Changing the connecting rod only changes the position of the piston in the cylinder. Only the crankshaft determines the stroke of an engine.

Figure 18-17 The distance between the centerline of the main bearing journal and the centerline of the connecting rod journal determines the stroke of the engine. This photo is a little unusual because it shows a V-6 with a splayed crankshaft used to even out the impulses on a 90-degree, V-6 engine design.

Engine Measurement Displacement Displacement (engine size) is the cubic inch (cu. in.) or cubic centimeter (cc) volume displaced or how much air is moved by all of the pistons

Engine Measurement Displacement Most engines today are identified by their displacement in liters 1 L = 1,000 cc 1 L = 61 cu. in. 1 cu. in. = 16.4 cc

Engine Measurement Conversion To convert cubic inches to liters, divide cubic inches by 61.02 To convert liters into cubic inches, multiply by 61.02

Engine Measurement Calculating Cubic Inch Displacement Formula: Cubic inch displacement = π (pi) × R 2 × Stroke × Number of cylinders

Engine Measurement Calculating Cubic Inch Displacement Applying the formula to a 6-cylinder engine: Bore = 4.000 in. Stroke = 3.000 in.

Engine Measurement Calculating Cubic Inch Displacement Applying the formula to a 6-cylinder engine: π = 3.14 R = 2 inches

Engine Measurement Calculating Cubic Inch Displacement Applying the formula to a 6-cylinder engine: R 2 = 4 (2 2 or 2 × 2) Cubic inches = 3.14 × 4 (R 2 ) × 3 (stroke) × 6 (number of cylinders)

Engine Measurement Calculating Cubic Inch Displacement Applying the formula to a 6-cylinder engine: Cubic inches = 226 cubic inches

Chart 18-1 To find the cubic inch displacement, find the bore that is closest to the actual value, then go across to the closest stroke value.

Chart 18-1 (continued) To find the cubic inch displacement, find the bore that is closest to the actual value, then go across to the closest stroke value.

Engine Measurement Engine Size Conversion Many vehicle manufacturers will round the displacement so the calculated cubic inch displacement may not agree with the published displacement value

Chart 18-2 Liters to cubic inches is often not exact and can result in representing several different engine sizes based on their advertised size in liters.

Compression Ratio Definition Ratio of the difference in the cylinder volume when the piston is at the bottom of the stroke to the volume in the cylinder above the piston when the piston is at the top of the stroke

Figure 18-18 Compression ratio is the ratio of the total cylinder volume (when the piston is at the bottom of its stroke) to the clearance volume (when the piston is at the top of its stroke).

Compression Ratio Calculating Compression Ratio Formula: CR = Volume in cylinder with piston at bottom of cylinder Volume in cylinder with piston at top center

Compression Ratio Calculating Compression Ratio Example: What is the compression ratio of an engine with 50.3 cu. in. displacement in one cylinder and a combustion chamber volume of 6.7 cu. in.? CR = 50.3 + 6.7 cu. in. = 57.0 = 8.5 6.7 cu. in. 6.7

Figure 18-19 Combustion chamber volume is the volume above the piston when the piston is at top dead center.

Compression Ratio Changing Compression Ratio Factors that can affect compression ratio include: Head gasket thickness

Compression Ratio Changing Compression Ratio Factors that can affect compression ratio include: Increasing cylinder size

Torque and Horsepower Definition of Torque Rotating force that may or may not result in motion Measured as the amount of force multiplied by the length of the lever through which it acts

Torque and Horsepower Definition of Torque Twisting force measured at the end of the crankshaft and measured on a dynamometer

Torque and Horsepower Definition of Torque Engine torque is always expressed at a specific engine speed (RPM) or range of engine speeds Metric unit for torque is newton-meters ?

Torque and Horsepower Definition of Power Rate of doing work Power equals work divided by time

Torque and Horsepower Definition of Power Power is expressed in units of foot-pounds per minute and power also includes the engine speed (RPM) where the maximum power is achieved

Torque and Horsepower Horsepower and Altitude Power that a normal engine can develop is greatly reduced at high altitude

Torque and Horsepower Horsepower and Altitude According to SAE conversion factors, a nonsupercharged or nonturbocharged engine loses about 3% of its power for every 1,000 ft (300 m) of altitude

FREQUENTLY ASKED QUESTION What Is a Flat-Head Engine? A flat-head engine is an older type engine design that has the valves in the block. The valves are located next to the cylinders and the air-fuel mixture, and exhaust flows through the block to the intake and exhaust manifolds. ? BACK TO PRESENTATION Because the valves are in the block, the heads are flat and, therefore, are called flat-head engines. The most commonly known was the Ford flat-head V-8 produced from 1932 until 1953. Typical flat-head engines included: Inline 4-cylinder engines (many manufacturers) Inline 6-cylinder engines (many manufacturers) Inline 8-cylinder engines (many manufacturers) V-8s (Cadillac and Ford) V-12s (Cadillac and Lincoln)

FREQUENTLY ASKED QUESTION What Is a Rotary Engine? A successful alternative engine design is the rotary engine, also called the Wankel engine after its inventor, Felix Heinrich Wankel (1902–1988), a German inventor. The Mazda RX-7 and RX-8 represent the only long-term use of the rotary engine. The rotating combustion chamber engine runs very smoothly, and it produces high power for its size and weight. ? BACK TO PRESENTATION The basic rotating combustion chamber engine has a triangular-shaped rotor turning in a housing. The housing is in the shape of a geometric figure called a two-lobed epitrochoid. A seal on each corner, or apex, of the rotor is in constant contact with the housing, so the rotor must turn with an eccentric motion. This means that the center of the rotor moves around the center of the engine. The eccentric motion can be seen in Figure 18–14.

FREQUENTLY ASKED QUESTION Where Does an Engine Stop? When the ignition system is turned off, the firing of the spark plugs stops and the engine will rotate until it stops due to the inertia of the rotating parts. The greatest resistance that occurs in the engine happens during the compression stroke. ? BACK TO PRESENTATION It has been determined that an engine usually stops when one of the cylinders is about 70 degrees before top dead center (BTDC) on the compression stroke with a variation of plus or minus 10 degrees. This explains why technicians discover that the starter ring gear is worn at two locations on a 4-cylinder engine. The engine stops at one of the two possible places depending on which cylinder is on the compression stroke.

TECH TIP How Fast Can an Engine Rotate? Most passenger vehicle engines are designed to rotate at low speed for the following reasons. Maximum efficiency is achieved at low engine speed. A diesel engine used in a large ship, for example, will rotate at about 100 RPM for maximum efficiency. Piston ring friction is the highest point of friction in the engine. The slower the engine speed, the less loss to friction from the piston rings. BACK TO PRESENTATION The slower the engine speed, the less loss to friction from the piston rings. However, horsepower is what is needed to get a vehicle down the road quickly. Horsepower is torque times engine speed divided by 5,252. Therefore, a high engine speed usually indicates a high horsepower. For example, a Formula 1 race car is limited to 2.4 liter V-8 but uses a 1.6 in. (40 mm) stroke. This extremely short stroke means that the engine can easily achieve the upper limit allowed by the rules of 18,000 RPM while producing over 700 horsepower. The larger the engine, the more power the engine is capable of producing. Several sayings are often quoted about engine size: “There is no substitute for cubic inches.” “ There is no replacement for displacement.” Although a large engine generally uses more fuel, making an engine larger is often the easiest way to increase power.

FREQUENTLY ASKED QUESTION Is Torque ft-lb or lb-ft? The definition of torque is a force (lb) applied to an object times the distance from that object (ft). Therefore, based on the definition of the term, torque should be: lb-ft (a force times a distance); Newton-meter (N-m) (a force times a distance) However, torque is commonly labeled, even on some torque wrenches as ft-lb. ? BACK TO PRESENTATION

TECH TIP Quick-and-Easy Engine Efficiency Check A good, efficient engine is able to produce a lot of power from little displacement. A common rule of thumb is that an engine is efficient if it can produce 1 horsepower per cubic inch of displacement. Many engines today are capable of this feat, such as the following: BACK TO PRESENTATION Ford: 4.6 liter V-8 (281 cu. in.): 305 hp Chevrolet: 3.0 liter V-6 (207 cu. in.): 210 hp Chrysler: 3.5 liter V-6 (214 cu. in.): 214 hp Acura: 3.2 liter V-6 (195 cu. in.): 260 hp An engine is very powerful for its size if it can produce 100 hp per liter. This efficiency goal is harder to accomplish. Most factory stock engines that can achieve this feat are supercharged or turbocharged.

Halderman ch018 lecture

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