AUTOMOBILE Flashcards
Automobile Engines - General Information
Cars use internal combustion engines, meaning the fuel is burned inside the engine. Steam engines are the opposite; they are external combustion engines meaning the fuel is burned outside the engine. All car engines, including diesel engines, utilize the Otto Cycle.
Otto Cycle Engine
A mix of fuel and air is brought inside a closed space, called a cylinder. The mix is compressed and then explodes. The explosion moves a piston, which rotates the crankshaft. The crankshaft is connected through the drive train to the driving wheels, which move the car. Waste heat from the explosions is removed by the cooling system.
Otto Cycle - Intake
The piston moves down, creating a partial vacuum in the cylinder. The fuel-air mixture enters the cylinder through the open intake valve. The exhaust valve is closed.
Otto Cycle - Compression
Both valves are closed. The piston moves up, compressing the fuel-air mixture to about ten times atmospheric pressure.
Otto Cycle - Power
The spark plugs fire, starting an explosion inside the cylinder. The resulting high pressure pushes the piston down.
Otto Cycle - Exhaust
The piston moves up again, with the exhaust valve open and the intake valve closed. The piston pushes burned exhaust gases into the exhaust manifold and out of the engine.
Cylinder and Piston
The cylinder is the heart of the internal combustion engine, where combustion takes place. It is a finely machined chamber holding a piston that slides up and down. Thin rings called piston rings seal the gap between the cylinder and the piston, containing the explosions and increasing efficiency.
Cylinder Head
A complex metal casting that closes the top of the cylinders. The head is bolted to the engine block.
Head Gasket
Separates the head and the block, creating a seal between two rigid objects that would otherwise leak.
Spark Plug
These electrical devices create a spark when they get a high voltage jolt of electricity from the ignition system. Spark plugs are screwed into the cylinder head and should be replaced periodically.
Connecting Rods and Crankshaft
Change linear motion into rotary motion. Connecting rods are attached to the crankshaft by the main bearings. The crankshaft rotates on journal bearings attached to the engine block.
Valves and Valve Train
Valves admit fresh fuel and air and discharge burned fuel and air. Consult ASVAB prep books for more details and diagrams.
Firing Order
To make the engine run smoothly, nearby cylinders do not ignite in sequence. The engine’s firing order is spread amongst the engine.
Lubrication System
Engines have tubes and passages that bring oil to contact points. A gear-driven oil pump pushes oil through these passages, lubricating piston rings and increasing compression efficiency.
Oil
Oil needs regular replacement as it gets dirty and wears out. Filters also need replacing. Recycle used oil; do not dump it. Burning oil may indicate worn rings or cylinders.
Viscosity
Measures the thickness of oil, rated by SAE numbers from very light (SAE 5) to heavy (SAE 90). Regular driving oil is typically SAE 30 to 40.
Cooling System
Only about 30% of energy from gasoline is converted to drive energy; the rest becomes waste heat. Coolant prevents overheating, including rust inhibitors and antifreeze.
Water Jackets
Tiny holes in the engine and cylinder block allow coolant to reach all engine parts.
Radiator
Coolant flows through water jackets to the radiator, which has tubes covered by fins and is located near the front of the engine for cooling.
Radiator Fan
Pulls air through the radiator, removing heat from the tubes.
Coolant Mixture Note
Always use a 50-50 antifreeze and water mixture to prevent coolant from freezing, remaining liquid down to about -30°F.
Water Pump
Located on the front of the crankshaft, circulates coolant through the engine. If it fails, the engine can overheat and incur damage.
Troubleshooting - Ping Sound
A ping or knocking sound during acceleration often indicates a need for higher octane gasoline.
Troubleshooting - Squealing Noise
A squealing noise that increases with engine speed may indicate a loose or worn fan belt.
