MECHENG236 - Internal Combustion Engines

Question 1

What is a combustion engine?

Answer 1

Device to convert energy stored in fuel to mechanical energy

Question 2

What is an INTERNAL combustion engine?

Answer 2

Combustion engine where the expansion of the high temperature gases caused by combustion applies direct force to a component of the engine

Question 3

What is an EXTERNAL combustion engine?

Answer 3

Involves heat from combustion being transferred to another working fluid

Question 4

Why use IC engine?

Answer 4

Mobility and long range/duty cycle
Energy density
Electricity not readily available
The IC engine is often used to generate electricity

Question 5

Main parts of the engine

Answer 5

Intake manifold
Camshaft pulley
Timing belt drive pulley
Cylinder head cover
Cylinder head
Exhaust manifold
Engine block
Oil pan

Question 6

Four stroke working cycle

Answer 6

1. Intake (suck)
   - piston moves downward. Fuel and air (mixture) drawn into the engine
2. Compression (squeeze)
   - As piston rises, inlet valve closes. Flywheel momentum drives the piston upward, compression the fuel/air mixture
3. Power (bang)
   - Near the top of the compression stroke, the spark plug fires, igniting the compressed fuel. As the fuel burns it expands, driving the piston downward.
4. Exhaust (blow)
   - At the bottom of the power stroke, the exhaust valve is opened by the cam/lifter mechanism. The upward stroke of the piston drives the exhausted gases out of the cylinder.

Question 7

What is the four stroke cycle known as

Answer 7

Otto cycle

Question 8

Two stroke engines relative to 4 stroke

Answer 8

Two stroke has:
- simpler components, no cam shaft or valves
- better suited to single cylinder
- unique design challenges: intake should mix with exhaust, seals must cross ports.

4 stroke: more fuel efficient and have lower emissions
2 stroke: fewer parts, lower cost, higher power to weight ratio, better torsional force pattern
4 stroke: run efficiently across large rpm range
2 stroke: run at higher engine speeds and tend to have limited power bands where they operate the best

Summary: 4-stroke generally preferred, but 2-stroke can be better power source for portable machinery e.g. chain saws, compressors, blowers, vacs, and small vehicles e.g. go-karts and motocross. Electric motors growing in these spaces.

Question 9

Largest ICE in the world

Answer 9

RTA96-C
2 stroke turbocharged low-speed diesel engine

Question 10

Wheel vs engine horsepower

Answer 10

Engine hp is almost irrelevant due to losses or inefficiencies in drivetrain (gearbox, diff)
Wheel hp is true measurement of cars overall power as it measures how much all the other systems transmit to the wheels.

Question 11

Spark vs compression ignition: How power is controlled

Answer 11

SI: Power controlled by amount of air that is let into the engine
CI: Power controlled by the quantity of fuel injected

Question 12

4 cylinder firing order

Answer 12

1, 3, 4, 2
At any time instance, one cylinder is always in power stroke

Question 13

Three ways energy of fuel is consumed and percentage rule of thumb

Answer 13

33% produces useful power output
33% is lost in the exhaust
33% is lost to the cooling system

Question 14

Real-life combustion emissions

Answer 14

Hydrocarbon emissions from unburned fuel and oil
Carbon monoxide is a byproduct from incomplete combustion (result of a rich mixture)
Oxides of Nitrogen results from high temperature and pressure during the combustion process

Question 15

What is a catalytic converter

Answer 15

Filters out harmful byproducts in the exhaust gases and burns them up. Main purpose to reduce harmful emissions, it also improves car’s efficiency