In-Line Engine: Design and Function

In-Line Engine

• Typically has four or six cylinders in an upright or inverted arrangement along the crankcase.
• Having more than six cylinders is rare due to cooling challenges for rear cylinders and the required crankshaft length.
• In a four-cylinder engine, four power strokes occur every two crankshaft revolutions.
• Firing orders like 1,3,4,2 or 1,2,4,3 help ensure smooth operation.
• A camshaft, driven at half engine speed, operates the valves using push rods and rockers.
• The eight cams (two per cylinder) open/close intake/exhaust valves based on firing order and valve timing.
• In a six-cylinder engine, six power strokes happen every two crankshaft revolutions.
• Each cylinder fires every 120º of crankshaft movement.
• Crankshafts with throws (offset portions containing crankpins) are arranged accordingly.
• The camshaft, driven at half engine speed, has suitably arranged cams.
• A typical six-cylinder engine firing order is 1,4,2,6,3,5, but alternative orders exist with different crankshaft designs.

Horizontally Opposed Engines

• Cylinders (usually four or six) are arranged horizontally on opposite sides of the crankcase.
• Engines typically have individual connecting rods on separate crankpins, creating staggered cylinders.
• A single camshaft, above or below the crankshaft, drives valves in both cylinder banks at half engine speed.
• Inlet valve cams may be shared by opposite cylinders.
• A six-cylinder engine can have nine cams: six exhaust cams and three shared inlet cams.
• To shorten the engine, a four-cylinder has three crankshaft bearings, while a six-cylinder has four.
• In a six-cylinder engine, throws are arranged at 120° intervals due to six firing strokes per two crankshaft revolutions.
• The normal firing order for a six-cylinder engine is 1,4,5,2,3,6, but different orders are possible.

V-Type Engine

• Cylinders are arranged in two rows or banks, forming a V-shape at a 90, 60, or 45-degree angle.
• These engines always have an even number of cylinders in each row.
• Two sets of connecting rods operate on the same crankpin because the cylinder banks are opposite.
• This design reduces weight compared to in-line engines.
• The frontal area is only slightly larger than in-line engines, allowing for streamlined engine cowlings.
• If cylinders are above the crankshaft it's an upright V-type, when below, it's an inverted V-type
• Inverted designs allow for better pilot visibility.

Otto Cycle

• The Otto cycle is the standard cycle for spark-ignition (SI) internal combustion engines.

Otto Cycle Processes

• Process 1-2 (Intake): Inlet valve opens, the piston moves to admit fuel-air mixture at constant pressure.
• Process 2-3 (Compression): Valves are closed, the piston compresses the mixture to minimum volume.
• Process 3-4 (Combustion): Spark ignites the mixture, causing combustion, increasing temperature and pressure.
• Process 4-5 (Expansion): Combustion products do work on the piston, decreasing pressure and temperature.
• Process 5-6 (Blow Down): Exhaust valve opens, dropping the pressure.