Week 3, Chapter 66 - Gasoline Exhaust Emissions Flashcards
The air we breathe is composed of what two gases?
Nitrogen and Oxygen
Emission control systems are designed to do what?
Limit pollution
What causes emission pollution?
Storing and burning various fuels
Emissions from current gasoline-fueled motor vehicles usually come from three main sources…
- The fuel system
- The crankcase
- The tailpipe
Fuel vapors that escape into the atmosphere are called ________________
Evaporative emissions
Pollutants release from the exhaust in the form of gases called _______________________
Tailpipe emissions
Blowby gases from the crankcase that leak into the atmosphere are called _______________
Crankcase emissions
____ drive cycle is used to certify the emission output of vehicles and ensure they meet regulatory standards
FTP
EPA requires a ________________ to alert the driver of an emission system fault
Warning light
Regulated air pollutants can be divided into two groups:
Gases and particulates
Two categories of emissions:
Harmful and nonharmful
Water (H2O), nitrogen (N2) and oxygen (O2) are all examples of what category gas?
Nonharmful
Carbon monoxide (CO), hydrocarbons (HC), carbon dioxide (CO2), oxides of nitrogen (NOx), sulfur dioxide (SO2), and particulates are all examples of what category gas?
Harmful
- Molecules of unburned gasoline
- Evaporative fuel emissions also a source
- When testing with a 5-gas analyzer readings should be less than 100ppm
Hydrocarbons (HC)
- Fuel is absorbed into oil on cylinder walls
- Fuel is not adequately mixed with air
- Misfires
- Very rich or lean mixtures that cause misfires
These are all causes of what?
Hydrocarbon emissions
_______________ is formed when carbon molecules join with oxygen molecules during combustion. Should be around 12-15%
Carbon dioxide
- Part of the air in the air/fuel mixture
- Not a pollutant
- When testing with a 5-gas analyzer, levels should read 0-2%
Oxygen
- A byproduct of combustion
- Rich indicator
- When using a 5-gas analyzer, readings should be less than 0.5%
Carbon monoxide
- Formed when nitrogen and oxygen molecules combine at high temperature
- A byproduct of excessive heat
- Most accurately tested under a load
Oxides of nitrogen (NOx)
What are the main strategies used by companies to meet emission standards?
- Design engine to reduce emissions
- Control air-fuel mixture
- Warm up engine quickly
- Integrate precombustion and postcombustion
_______________________ focuses on assuring that combustion happens in a controlled and complete manner
Precombustion treatment
What are the two primary precombustion emission control systems?
Heated air intake system
Exhaust gas recirculation system
_______________________ systems deal with the remaining pollutants that are left over from the combustion process
Postcombustion emission control
What are the three primary postcombustion systems?
- Positive crankcase ventilation (PCV)
- Secondary air injection system
- Catalyst system
Liquid fuel will not bur easily in the cylinder and must be in a ________ form for proper combustion
Vapor
Throttle body injection and carbureted systems may help ________ the exhaust through an intake crossover to help vaporize fuel
Route
_______________ use the air around hot exhaust manifolds to blend with outside air, to supply warm air at a predetermined temperature
Heated air intake systems
__________________ is used to preheat the engine during cold start
Cold start emissions reduction (CSER)
Exhaust gas recirculation (EGR) system is designed to do what?
Control oxides of nitrogen (NOx)
Newer engines use _______________ to draw some exhaust gases back into the cylinder
Variable valve timing
An ________________ connects a passage from the exhaust port, or manifold, to the intake manifold
EGR valve
What are the 5 gases that are tested in a 5-gas analyzer?
- Hydorcarbon (HC)
- Carbon Monoxide (CO)
- Nitrous Oxide (NOx)
- Carbon Dioxide (CO2)
- Oxygen (O2)
During combustion, an amount of fresh air-fuel mixture is replaced by _____________________
Inert exhaust gases
At wide-open throttle (WOT), the EGR system is typically ______________
Shut off
Older vehicles use _____________ solely to operate the EGR system
Vacuum controls
Many vacuum controlled EGR systems also use a _______________________
Temperature-sensitive vacuum valve
What are two common types of electric EGR valves?
- Pulse width modulated solenoid type
- Stepper motor EGR valve type
What does the pulse width modulation system do?
Uses a spring-loaded valve that is opened by an electric solenoid and closed by the spring
The stepper motor EGR valve controls _____________ much more precisely
EGR flow
PCM sends signal to the stepper motor, which can do what?
Open or close the valve one step at a time
Most PCM-controlled EGR systems incorporate a feedback loop, called a __________
Monitor
What are the three main types of PCV systems?
- Variable orifice
- Fixed orifice
- Separator
In which PCV system does a replaceable, spring loaded PCV valve regulate gas flow?
Variable orifice
The PCV system is designed to remove blowby gases which may cause excessive ___________ emissions
Hydrocarbon
Modern PCV systems are the ___________ type
Closed (sealed)
What PCV system usually involves a screw-in fitting with a small hole drilled in it
Fixed orifice
How does a fixed orifice type PCV system work?
The hole creates a predetermined vacuum leak that draws a predetermined amount of crankcase vapors from the crankcase
What type of PCV system involves a valve that is hooked to the pressure side of the crankcase, an oil return line at the bottom of the valve, and a suction line on the other side?
Separator
The separator type is used on _____________ applications
Turbocharged
Secondary air injection post-combustion is less common nowadays because of…
- Improved engine design
- More accurate fuel delivery
- Highly efficient three-way catalytic converters
What three valves does a secondary air injection system use to control airflow in the system?
- Air switching valve
- Air diverter valve
- Check valve
Early secondary air injection systems used a ___________________ in the vacuum line to control the switching valve
Thermal vacuum switch
What is the main job of catalystic converters?
To perform a final cleanup of the tailpipe emissions
What are the two types of catalytic converters?
- Oxidizing
- Reduction
The ________ catalyst contains a platinum and rhodium coating, which helps to reduce the oxides of nitrogen molecules into their base compounds
Reduction
More recent versions of the two-way (and three-way) catalytic converters are designed with a ___________ catalytic element
Honeycomb
The PCM can control oxygen in the exhaust by adjusting the _________________
Air-fuel ratio
The first oxygen sensor indicates the amount of oxygen in the exhaust stream as it leaves the ______________
Cylinders
The second oxygen sensor measures the oxygen oxygen in the exhaust stream after it leaves the _______________________
Catalytic Converter
The oxygen content is normally __________ after the converter and results in higher and steadier oxygen sensor voltage
Lower
Catalytic _____________ happens when the catalyst becomes coated by a substance such as lead, silicone, or carbon
Contamination
Catalytic __________ can cause the catalyst material to burn off the substrate, rendering it inoperative
Overheating
Catalytic _________________ can happen due to an object such as a large rock striking the converter or from thermal shocks
Physical damage
EVAP emission control systems are designed to ensure that…
Hydrocarbons are not released into the atmosphere
EVAP system stores fuel vapors in the _____________ until the PCM’s command
Charcoal canister
The fuel cap may incorporate a ____________________
Pressure relief valve
Modern tanks also contain a(n) ______________________ that allows for the expansion of liquid fuel on hot days
Expansion volume
A __________________ allows a space for liquid fuel to separate from the vapors and return to the fuel tank
Liquid-vapor separator
What is the process of drawing fresh air up through the activated charcoal?
Purging
What is the purpose of purging?
To prepare the canister to absorb fuel vapors the next time the vehicle is not running
_______________________ is a critical part of reducing one of the major sources of hydrocarbon emissions
Capturing evaporated fuel vapors
If a fuel is more __________, it is able to evaporate quickly and easily
Volatile
Electronic controls in the EVAP system allow for more precise _____________________
Purge control
Purge valve can be opened by an __________________ or __________________
Integrated solenoid
Stepper motor
_____________ style can be either on/off or pulse-width-modulated
Solenoid
In a _________________ style, the PCM can progressively open and close the purge valve one step at a time
Stepper motor
A(n) ________ vapor control valve contains a float that rises with the fuel level and blocks off the vent hose when the tank is full
ORVR (Onboard Refueling Vapor Recovery)
The first indication of any trouble with the emission system is a ____
MIL (Malfunction Indicator Light)
Diagnosis of emission control systems starts with ________________
Verifying the concern
The PCM’s ______________________ and data stream can also help identify faults
Freeze-frame data
PCM’s _____________ capability may be helpful tooperate suspect components and observe the results
Bidirectional
What tool uses sensors to measure the level of gases in the exhaust stream?
Five-gas analyzer
Exhaust with a bluish tint means what?
Oil is being burned in the combustion chamber (piston oil control rings are worn)
Exhaust with a black color means what?
Overly rich air-fuel mixture
Exhaust with a white color means what?
Coolant is burning in the combustion chamber
