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This chapter provides an explanation of the principles of internal combustion engine operation, identification of engine parts, and an overview of various engine classifications. Topics covered include the operation of simple reciprocating engines, four-stroke engine operation, compression ratio, cylinder arrangement, camshafts, cylinder block construction, short and long blocks, engine displacement, valve arrangement, combustion chamber designs, direction of crankshaft rotation, firing order, companion cylinders, engine cooling, and spark and compression ignition.
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Chapter 1 Engine Operation
Objectives • Explain principals of internal combustion engine operation • Identify internal combustion engine parts by name • Explain various engine classification
Simple Reciprocating Engine • Cylinder • Piston • Connecting rod • Crankshaft
Four Stroke Engine Operation • Intake stroke • Compression stroke • Power stroke • Exhaust stroke
Compression Ratio • Comparison of volume at BDC and at TDC • If compression ratio is 8:1 • Mixture is compressed to one-eighth its original volume • If compression ratio is 12:1 • Mixture is compressed to one-twelfth its original volume
Cylinder Arrangement • Up to eight or more cylinders (3,4,5,6,8) • Arranged inline • V style or opposed
Camshafts • Control the rate at which engine breathes • Located in either block or cylinder head • Driven by crankshaft using gears, chain, or belt • Turn one-half speed of crankshaft
Cylinder Block • Includes oil galleries and water jackets • Can be constructed from cast iron or aluminum • Cast around a sand or foam mold called a core • In lost foam casting (LFC) the form is “lost” or burned during the pour • Made of expendable polystyrene beads (styrofoam) • V type blocks are cast in two rows • Called banks
Short and Long Block • Short blocks • Crankshaft, pistons, rods, camshaft, and cam drive components • Long block • Short block plus cylinder heads
Short and Long Block • Oil pan, flywheel, harmonic balancer and timing chain cover may be mounted on both the short and long block
Engine Displacement • Engines classified by their displacement • Displacement is total volume pistons displace in cylinders • Formula to determine displacement • Bore² × Stroke × .7854 × Number of cylinders
Valve Arrangement • Modern engines use and overhead valve (OHV) arrangement known as I-head or valve-in-head
Combustion Chamber Designs • Primary designs • Hemi, wedge, pent-roof, stratified charge • Combustion chamber • Area in cylinder head into which air-fuel mixture is compressed
Combustion Chamber Designs • Turbulent and nonturbulent designs • Turbulent • Wedge • Nonturbulent • Hemi
Direction of Crankshaft Rotation • Front of engine is side opposite the transmission • Longitudinally mounted engines turn clockwise when viewed from the front • Transverse mounted engines also follow this standard • Although a few engines (ie Honda) rotate in the opposite direction
Firing Order • Sequence in which cylinders fire • Firing order typically does not follow cylinder numbering • An example of a v8 firing order • 18436572
Companion Cylinders • Engine with even number of cylinders will have companion cylinders • Pair of pistons go up and down together • One cylinder on compression stroke while other is on exhaust stroke
Engine Cooling • Use both air cooling and liquid cooling • As engine temperature rises • Amount of NOx (oxides of nitrogen) rises • Liquid cooled engines have water jackets to cool areas around cylinders • Coolant is moved through system by water pump
Engine Cooling • Coolant mixture • 50% coolant and 50% water • Dissimilar metals found in engine can cause electrolysis in coolant • Causes corrosion and deterioration of metals
Spark and Compression Ignition • Conventional spark ignition systems • Spark plug to ignite air-fuel mixture • Diesel engines • Compression of engine to ignite air-fuel mixture
Two Stroke Cycle • Outboards, chainsaws, motorcycles • Power stroke every revolution in crankshaft • Oil must be mixed with gasoline • Lubricates lower engine bearings