Motive Power Types— Spark-Ignition (SI) Engines CHAPTER 44 Motive Power Types— Spark-Ignition (SI) Engines

Introduction Internal combustion engine is irreplaceable. Hauls food and water, delivers passengers, saves lives

Principles of Thermodynamic Internal Combustion Engines (1 of 3) Science branch dealing with heat and energy Used in internal combustion engine Moves vehicle down road and provides power Once powered all equipment Steam engines

Principles of Thermodynamic Internal Combustion Engines (2 of 3) External combustion engines A. Steam engine. B. Stirling engine.

Principles of Thermodynamic Internal Combustion Engines (3 of 3) <insert fig 44- 2> Stirling engine Internal replaced external combustion. Gas and diesel engines ICE classified in two ways Piston engines are SI or CI engines.

Principles of Engine Repair (1 of 10) Operate on physics and thermodynamics Understanding will help diagnose. Tightly packed molecules increase expansion pressure. Burning black powder = fire.

Principles of Engine Repair (2 of 10) Pressure and temperature Directly related Cylinder with moveable plunger Diesel engines use same principle. Heating increases molecule movement.

Principles of Engine Repair (3 of 10) Pressure changes temperature. Temperature changes pressure.

Principles of Engine Repair (4 of 10) <insert fig 44- 6> Temperature and energy Measures energy Latent heat in various fuels Expressed in Btu

Principles of Engine Repair (5 of 10) Pressure and volume Inversely related

Principles of Engine Repair (6 of 10) Force, work, and power Force: effort to push or pull Compressed spring/cable moves to create work. Power: rate or speed at which work is performed

Principles of Engine Repair (7 of 10) Power and torque Torque: twisting force Unit of measurement: ft-lb or newton meters Amount of torque at crankshaft and speed of turning 1 hp = 33,000 ft-lb/min

Principles of Engine Repair (8 of 10) Power and torque (cont’d) Calculate twisting by adding distance moved and time. Converting torque to work requires movement.

Principles of Engine Repair (9 of 10) Torque vs. horsepower Torque: twisting or turning force and horsepower Naturally aspirated engines Engine rpm rises faster as torque falls.

Principles of Engine Repair (10 of 10) Engine load factor Used in regard to diesel engines Gives power as an average

Four-Stroke Spark-Ignition Engines (1 of 5) SI engines operate on four-stroke principle. Takes four strokes to complete one cycle Can be simple or complicated

Four-Stroke Spark-Ignition Engines (2 of 5) Basic four-stroke operation One stroke out of the four delivers energy. Compression stroke Ignition occurs as piston reaches TDC. Exhaust stroke: end of power stroke

Four-Stroke Spark-Ignition Engines (3 of 5) Engine measurement—size ICEs designated by volume pistons displace Cylinder bore Piston stroke Piston displacement Engine displacement Compression ratio

Four-Stroke Spark-Ignition Engines (4 of 5) Atkinson and Miller cycle engines Variations on four-stroke engine Use larger throttle opening for power Efficient within range Lower max operating rpm

Four-Stroke Spark-Ignition Engines (5 of 5) Scavenging Uses column of moving air Engine displacement.

Components of Spark-Ignition Engines (1 of 9) Widely used to power passenger vehicles Main power plant Gains in manufacture Divided into two assemblies The compression ratio of an engine is found by taking the volume of the cylinder at BDC and comparing it to the volume at TDC. In this example, a 9:1 compression ratio is found.

Components of Spark-Ignition Engines (2 of 9) Short block and long block Subassembly may be used. The engine contains many parts that work together to power the vehicle.

Components of Spark-Ignition Engines (3 of 9) Cylinder block, crankshaft, flywheel Block is largest part of engine. Oil pan completes crankcase. Crankshaft is composed of cast iron or steel. Crankshaft has main journals.

Components of Spark-Ignition Engines (4 of 9) Connecting rod and piston Connecting rod is made of cast iron, steel, aluminum, or titanium. Rod causes piston movement. Piston is composed of aluminum or synthetic materials. Head is exposed to heat and pressure.

Components of Spark-Ignition Engines (5 of 9) Ring lands Areas between the ring grooves that support the rings as the piston moves.

Components of Spark-Ignition Engines (6 of 9) The oil pan Seals and holds oil Houses oil pump

Components of Spark-Ignition Engines (7 of 9) The cylinder head Made of cast iron or aluminum

Components of Spark-Ignition Engines (8 of 9) Engine cam and camshaft ICE uses poppet valves. Flathead engines had valves in block. Camshaft is mounted on top of cylinder head. Lobes open to hold and close valve.

Components of Spark-Ignition Engines (9 of 9) Camshaft specifications Base is rounded bottom part. Duration is used when designing lobe. High-performance engines have overlap. Two listings for cam specs

Valves (1 of 15) Open or close cylinder heads Intake controls flow of air/fuel in combustion chamber. Valve head is disc shaped.

Valves (2 of 15) Intake and exhaust valves Control ICE

Valves (3 of 15) Valve arrangement One of two methods L-head I-head

Valves (4 of 15) Mechanical and hydraulic valve train Combo of parts open and close engine valves. Adjustments are made by lifter.

Valves (5 of 15) Roller rockers and lifters Reduce friction and increase engine efficiency Arms have fulcrum. Arms increase lift into cam lobe. Friction loss occurs.

Valves (6 of 15) Valve clearance Amount of slack between rocker arm and valve stem

Valves (7 of 15) Valve timing Critical to proper ICE operation Factory setting

Valves (8 of 15) Theoretical four-stroke cycle engine valve timing Piston at TDC opens valve. Valves open and close sooner than described. Airflow creates velocity. Cam allows valve spring to close.

Valves (9 of 15) Burning air/fuel expands air. Some degree of overlap at TDC and BDC Not much inertia Large overlap at cranking speeds Timing controlled by cam lobes Advance or reduce power

Valves (10 of 15) Variable valve timing Benefit to engine performance Valve timing managed by electronic modules Vane-type phaser Can be used on any arrangement

Valves (11 of 15) Variable valve timing (cont’d) Inert gas does not react chemically Variable cam timing is controlled by PCM

Valves (12 of 15) Valve train drives Driven by camshaft Chains louder than belts Freewheeling engine Timing chain differs between cam-in-block and OHC.

Valves (13 of 15) Valve train drives (cont’d) OHC requires longer timing chains. Belts use toothed or cogged belt.

Valves (14 of 15) Intake manifold Part of air intake/induction Many changes

Valves (15 of 15) Exhaust manifold Output side of engine breathing apparatus

Two-Stroke Spark-Ignition Engines (1 of 4) Produce large power to weight ratio Every other stroke is power.

Two-Stroke Spark-Ignition Engines (2 of 4) Basic two-stroke cycle engine principles Differs from four-stroke SI engine One revolution for every cycle in two-stroke Piston movement creates suction. Piston moves up to TDC. Piston moves up, compression in cylinder.

Two-Stroke Spark-Ignition Engines (3 of 4) Two-stroke intake system Piston port Reed valve No rotary valve

Two-Stroke Spark-Ignition Engines (4 of 4) Four- and two-stroke engine differences Lube from mixing oil with gas Benefits Downfalls

Rotary Combustion Spark-Ignition Engines (1 of 5) Fewer parts used Increased power and smaller engine Rotary combustion in many applications

Rotary Combustion Spark-Ignition Engines (2 of 5) Basic principles Not as common No reciprocating piston Smooth and vibration free Basic principles as rotary engine Intake cycle

Rotary Combustion Spark-Ignition Engines (3 of 5) Basic components of rotary engine Mounted in oval-shaped housing Two spark plugs Rotor has three apexes. Combustion chamber is formed by hollows in rotor flanks. Teeth of rotor walk around stationary gear.

Rotary Combustion Spark-Ignition Engines (4 of 5) Engine power pulses Three power pulses per rotation

Rotary Combustion Spark-Ignition Engines (5 of 5) Renesis rotary engine Same as conventional Primary, secondary, auxiliary ducts Three intake ports Two fuel injectors/rotor

Summary (1 of 11) Internal combustion engines are common. Combustion engines are piston or rotary. Piston engines are spark or compression ignition. Pressure and temperature are directly related. Internal combustion engines heat a gas. Pressure and volume are inversely related.

Summary (2 of 11) Force causes movement. Work = distance moved × force applied. Power = distance × force/time in minutes. Engine power is measured in torque. Torque is called engine output. Horsepower is the speed of torque.

Summary (3 of 11) Load factor = time a vehicle can operate at max speed and power. Piston stroke = distance traveled from TDC to BDC. Internal engines are two- or four-stroke. Five events must occur in a four-stroke engine. Compression ratio is based on cylinder volume.

Summary (4 of 11) Piston displacement: bore squared × 3.14 × stroke ÷ 4. Engine displacement: piston displacement × number of engine cylinders. Miller and Atkinson are variations of the four-stroke engine. Miller has engine-driven compressor. Atkinson has lower power output and torque.

Summary (5 of 11) Valve overlap: time intake and exhaust valves are open. There are 11 major components of an internal combustion engine. Cylinder block includes additional parts. Crankshaft: converts piston’s reciprocating motion into rotary motion. Flywheel stores energy from piston.

Summary (6 of 11) Connecting rod connects piston to crankshaft. There are 7 components of the piston. Gases can leak past piston rings. Intake manifolds deliver air to cylinder head. Oil is stored in the oil pan. Camshaft opens valves.

Summary (7 of 11) There are 4 parts to a camshaft. Engineers must consider several issues when designing camshaft lobes. There are 4 parts of an intake valve. Intake valve is large and runs cool. Exhaust valves are small and run hot.

Summary (8 of 11) Modern engines are arranged in I-head. Valve lifter is hydraulic or mechanical. Roller rocker arms act as levers. Valve clearance must be accurate. Timing of valves is critical. Valve timing can be modified.

Summary (9 of 11) Variable valve timing is available. Cam actuators can be twisted. ECM controls variable cam timing. Pulse width modulation signals regulate solenoids. Engines are freewheeling or interference. Two-stroke engines use piston to open and close exhaust ports.

Summary (10 of 11) Internal combustion engine events are controlled by a piston. Two-stroke engines use reed or rotary valve. Two-stroke engines don’t use camshaft or valve train. Four-stroke engines are more environmentally friendly.

Summary (11 of 11) Rotary and Wankel engines use a rotor in place of a piston. Rotary engines have two spark plugs. Rotary engines have four phases. Faces of the rotor have a combustion chamber. Renesis rotary engine is fuel efficient. Renesis engine can be low output.

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