Engine test review

Engines review:

ENGINE FUNDAMENTALS

> 4 stroke principles
	- A stroke is when a piston moves from TDC (Top dead center) to BDC (Bottom dead center) or vise versa
	- Intake, The valves intakes air-fuel mixture in, ready for compression
	- Compression, the piston moves up and compresses the gas so that it is easier and produce more power when ignited
	- Combustion, when the piston is on TDC, the compressed gas will be ignited, thus produce a downward motion with potential energy ready to be converted into kinetic energy via crankshaft
	- Exhaustion, when the piston finishes with it's downward motion from the combustion, exhaust valve will open and let the product from the combustion out, so that it can intake new gas and cycle starts again

	- In 4 strokes, the crank shaft turns twice

> 2 stroke engine cycle
	- 2 stroke engines are designed in a way that it only requires 2 strokes (piston goes up, then comes down) to complete a cycle with the task 4 stroke engines have

> Rotary engines
	- In a rotary engine, a triangular round shape object is in the middle, with a egg shaped housing, the rotary action can do intake, compression, ignition, and exhaust all at once.
	- This engine can be vibrate free, but more expensive than other average engines

> 4 stroke diesel engines
	- Very similar to 4 stroke engines
	- Instead of injecting the fuel mixture in intake stage, it only injects the air, when the air is compressed, the fuel is then injected.

> Engine block and pistons
	- An engine block is the largest piece on a engine
	- The upper part of the block carries the cylinders and the pistons.
	- usually the lower part is the crankcase and supports the crankshaft
	- Inline engines or smaller engines have 1 cylinder heads, others may have 2 or more cylinder heads
	- Most cylinder heads can be made of cast iron or Aluminum alloy, aluminum alloy is lighter than cast iron

	- The piston is connected to the crankshaft with a connecting rod
	- it transfers the energy from combustion to rotary motion on crankshaft
	- piston also performs compression in the 4 stroke cycle

	- connecting rod connects the piston to the crankshaft
	- the little end of the connecting rod is fastened to the piston, the larger end is connected to the crankshaft

VALVE AND VALVE TRAINS

> Valves
	- gasoline engines must be controlled with valves since it manages the intake and exhaustion
	- in a 2 stroke engine, the piston itself can act as a valve since it can block off the intake of exhaust
	- almost all 4 stroke engines uses valves
	- the valves have to be tough, they open and close over 30 times a second, exhaust valves have to stand huge temperature and can be red hot
	- valves cannot go soften at high temperatures
	- surface treatments are used to protect and prevent wear, burning and corrosion
	- valves are made of nickel based alloys, higher performance valves uses titanium alloys

> Valve seats
	- poppet or mushroom valves have 2 main parts, the head and the stem, stem is the coolest part of the valve
	- when the valves are in operation, the heat is transferred from the head to the seat, the valve seat is then cooled by the coolant
	- the size of the valve seats is important, a narrow seat have less surface area contacted with the head, a wider seat is better because it has more surface area, therefore cools better