What are four functions of an air induction system?
- Clean the air supply
- Silence the air inflow
- Provide air for combustion
- Cool the air
- Allow extra air inflow with blowers and turbos
What are the two main air induction systems?
- Naturally aspirated
- Turbo/supercharged
What is the main difference between a four-stroke and two-stroke naturally aspirated engine?
The two-stroke uses the aid of a blower to increase volumetric efficiency, whereas a four stroke uses only the natural vacuum created by combustion
The volumetric efficiency of a naturally aspirated engine, in a perfect world, is:
75-80%
Identify the 3 components of the air cleaner assembly:
- Pre-cleaner
- Air filter
- Air filter housing
- Air inlet restriction gauge
WHat is the purpose of a pre-cleaner?
It filters out large contaminants from the air, before it enters the min portion of the air cleaner. it may be able to remove 80%= of the larger contaminants.
Identify two benefits of an automatic dust ejection system:
- Reduces downtime as the dust is automatically ejected during vehicle operation
- Reduces labor costs as it is self cleaning
How are dry filter elements suitable air filters, despite their small size?
They are constructed of pleated paper, so though they are compact they have a large surface area to filter contaminants from the air.
What is the purpose of the SECONDARY air filter?
It is a final filter to stop contaminants from entering the engine in the event of the primary filter failing.
What is the purpose of the air inlet restriction gauge?
It identifies the amount of restriction the air inflow is experiencing after the filter, and is used to determine when the filter needs to be serviced.
What is meant by a CONSTANT TENSION (constant torque) hose clamp?
It is a clamp that uses a spring device to maintain an even clamping tension, despite hose deformities caused by temperature or pressure changes.
True or False:
Air inlet shutdown devices are used to protect the engine from air that heavily contaminated.
False: The devices generally protect the engine from over-speeding/running away.
What are two disadvantages of an OIL BATH type filter assembly?
- If the oil level is too high, it could get drawn into the engine (contaminants)
- If operations are on uneven ground, the oil level can change and become useless (not filter due to oil on one side of filter and not the other)
- When ambient temperature drops, oil in the reservoir thickens (preventing contaminants from getting stuck in it)
What is the primary function of an exhaust system?
Its primary function is to gather exhaust gases from cylinders, direct them to the silencing system, and then dispersing them into the atmosphere.
True or False:
Exhaust manifolds are used to collect exhaust gasses from the cylinders.
TRUE
True or False:
A function of the exhaust system is to eject dirt particles from the air cleaner.
FALSE: Dirt is ejected from the automatic dust ejection system, which is part of the air induction system.
Why would exhaust manifolds be constructed as a multi-piece design?
The multi-piece design would be used if engine access is limited or multiple cylinder heads are used.
True or False:
Exhaust piping may be rigid or flexible; flexible tubing is used when a bend in the system is required.
FALSE: Flexible piping is used when movement is needed between two fixed sections of exhaust piping, or between a pipe and major exhaust component (such as a muffler).
True or False:
Mufflers can be a STRAIGHT-THROUGH or REVERSE-FLOW design.
TRUE
True or False:
Fiberglass is used in mufflers to absorb noise pollution.
TRUE
What are two functions of the heat shield on an exhaust system?
- They prevent low grass/brush from contacting the hot muffler
- They prevent burn injuries to workers
- They protect the cab/sleeper from the heat of the muffler/exhaust stack
Why would the air induction system be inspected for leakage?
If there is leakage, contaminated air could enter the engine at those sites causing internal damage.
Why should the exhaust system be inspected for leakage?
The exhaust system contains pressurized gasses; inspection will prevent these gasses from getting into the engine, cab, and sleeper thus preventing carbon monoxide poisoning.
True or False:
Internal engine damage can be reduced by 80% when effective pre-cleaners are used.
TRUE
