SMOG TEST-EMISSION TEST-DRIVE CLEAN

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  1. admin

    admin Administrator Staff Member

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    By Peter, Associate Technical Writer, BAT Auto Technical

    Whatever one calls it, checking the emissions that come out of vehicle's tailpipe is here to stay.

    Governments of all levels whether Federal, State or Provincial have found it the political correct thing to do and strongly support it publicly.

    This is, hopefully, to help people understand emission testing and what can go wrong when a vehicle fails an emission test that we write this article. This in no means has all the answers or will it make one an emission expert. To fully understand emission would take several weeks in school and a strong background in mechanical repairs.

    The first things one has to understand is what emission gases are and what some of the terms used are.

    Following are the five gases, the short terms used and an explanation:

    1. HYDROCARBONS (HC - PPM)

    Hydrocarbons are unburned fuel. A properly running engine will produce some HC's. On most late model vehicles in good mechanical condition and equipped with functional emission controls, HC measured at the tailpipe will be very low.

    The presence of HC in the exhaust shows unused energy (fuel) going out the tailpipe.

    Excessive HC in vehicles is the result of incomplete combustion, which could be caused by ignition malfunction, mechanical faults, vacuum leaks or fuel control or fuel management problems.

    Example of:
    An electrical defect may be caused by a fouled spark plug, shorted or broken ignition wire or a carbon tracked distributor cap.

    A mechanical defect may be caused by a defective valve train component, weak or worn piston rings or excessive timing chain or belt wear, etc.

    2. CARBON MONOXIDE (CO - %)

    Carbon monoxide is formed when a hydrocarbon (like gasoline) tries to burn (oxide) in an oxygen poor environment. Only part of the energy in the hydrocarbons is released for useful power, the rest are not released energy because of poor combustion.

    CO therefore is a by-product of combustion.
    It is a tasteless, odourless gas, which is Toxic.

    CO is measured in percent (%) by volume. Eg: 1-% CO means 1% of a total 100% of exhaust gas consists of Carbon Monoxide.

    Engines in good operating condition properly adjusted and all sensors working will produce low CO readings. Vehicles that are equipped with emission devices produce even less.

    Excessive CO is created when and only when fuel is burned without sufficient air (O2) to allow for complete combustion, also known as oxygen starvation.

    3. OXIDES OF NITROGEN (NOx)

    NOX is the catchall name for a group of chemicals of different Nitrogen and Oxygen combinations. When enough NOx is present in the air combined with sunlight forms irritating smog when mixed other elements in the air.

    Nitrogen (N) makes up approximately 78% of the air we breath and the rest, approximately 21% is oxygen. The engines in today's vehicles use oxygen to operate and exhausts the nitrogen. NOx is formed when the combustion temperature exceeds 2500° F.

    Unfortunately an engine designed and tuned to produce low CO and HC produces high NOx The hotter an engine runs the more power it delivers, the more NOx it produces.

    Late Model vehicles operate with a very lean A/F mixture so the NOx is very high and a "three way Catalyst is incorporated converting CO, HC and NOx.

    A device called the E.G. (Exhaust Gas Recirculation) Valve was designed to lower the combustion temperatures by recirculating exhaust gasses back into the combustion chamber.

    NOTE:
    There is little the mechanic can do to control NOX emissions, except to make sure the engine and E.G.R. valve (on vehicles so equipped) are functioning properly.

    One of the keys to emission control techniques is controlling the air/fuel ratio. The point at which the A/F mixture burns efficiently for peak catalytic converter operation is called the Stoichiometric Point or ideal air/fuel mixture. At this point the HC, CO, O2 is near peak. The point at which complete combustion occurs is 14.7 to 1A/F ratio (called "Theoretically ideal").

    These three gases are what are looked at when an emission test is done and considered the most polluting.

    The following two gases are used basically for Diagnostic purposes.

    4. OXYGEN (O2- %)

    Oxygen is a plentiful element, forming about 21% of the earth's atmosphere. It combines easily with many materials (especially under flame conditions) to release heat energy.

    Like CO (Carbon Monoxide) oxygen is measured in percent (%) by volume. With oxygen present the converter can function properly, without oxygen the converter/reactor cannot convert the HC or CO it receives.

    Currently there are two systems in use, which supply O2 to the converter and air pump and a pulse air system. Both of these add O2 to the exhaust increasing the efficiency of converter/reactor.

    Oxygen and Carbon Monoxide are is an excellent indicator of a lean or rich running engine and in detecting ignition problems such as misfire and vacuum leaks.

    5. CARBON DIOXIDE (CO2 - %)

    Carbon Dioxide is the result of one carbon molecule joining with two oxygen molecules in the combustion chamber.

    Carbon Dioxide is one of the chemically correct, non-toxic by products of combustion.

    The amount of CO2 is an important diagnostic clue to the efficiency of the combustion process and is considered as the combustion efficiency indicator.

    The greater the percentage of CO2 in the exhaust, the more efficient the engine is running.

    Little notes of interest:

    Oxygen burns the “C” of the “HC and “CO2” is produced. This “CO2” is a harmless, colourless, odourless gas. Oxygen also reacts with the “H” of “HC” and produces “H2O” or water, which is emitted as vapour or steam from the tailpipe.

    If this process would take place as described, we would have little or no emission problems. Unfortunately, the combustion process in not always perfect and because of this we have other gases coming out of the tailpipe.

    These harmful byproducts which were described before are:
    Carbon Monoxide - (CO) - poisonous, odourless gas
    Hydrocarbons - (HC) - unburned fuel
    Oxides of Nitrogen - (NOX) - smelly poisonous irritant

    SULPHUR DIOXIDE EMISSIONS (Sox)

    With the advent of catalytic converters, Sulphur Dioxide Emissions have become evident. Oxides of Sulphur (SOX) result from the small amount of sulphur in gasoline. Sulphur content in gasoline is less than .1 %; this small amount of sulphur is emitted from the engine to the atmosphere.

    The sulphur is converted to Sulphur Dioxide in the combustion process, when the Sulphur Dioxide reaches the converter; it is further oxidized to Sulphur Trioxide. Under certain conditions it will combine with water vapour to form a Sulphur Acid mist.

    At present it is not one of the gases that make up the emission testing.

    NOTE:

    There is little the mechanic can do to control NOX emissions, except to make sure the engine and E.G.R. valve (on vehicles so equipped) are functioning properly.

    One of the keys to emission control techniques is controlling the air/fuel ratio. The point at which the A/F mixture burns efficiently for peak catalytic converter operation is called the Stoichiometric Point or ideal air/fuel mixture. At this point the HC, CO, O2 is near peak. The point at which complete combustion occurs is 14.7 to 1A/F ratio (called "Theoretically ideal").

    These three gases are what are looked at when an emission test is done and considered the most polluting.

    Some of the Common Causes of Excessive Exhaust Emissions

    Hi HC on Driving Test or High Idle Test

    - Vacuum leaks (hoses, EGR valve, intake manifold, and carburetor).
    - Ignition system malfunction (plugs, wires, coil)
    - Faulty computerized engine management and/or oxygen sensor
    - Faulty air injection system
    - Internal engine problem (burned valves, poor compression)
    - Failed Catalytic converter

    Hi HC at Idle Test

    - Ignition system malfunction (plugs, wires, coil)
    - Incorrect air/fuel mixture
    - Vacuum Leaks (hoses EGR, Intake manifold, carburetor)
    - Incorrect ignition timing and/or idle speed
    - EGR valve partially stuck open
    - Faulty fuel injector Operation
    - Internal engine problem (burned valves, poor compression)
    - Inoperative or missing catalytic converter
    - Air injection system failure

    Hi CO on Driving Test or high Idle Test

    Excessively rich mixture due to:

    - Carburetor malfunction
    - Dirty air filter, faulty choke
    - Faulty computerized engine management and/or Oxygen Sensor
    - Faulty fuel injection system
    - Faulty Thermostatic Air Cleaner (TAC) system
    - Defective evaporative canister purge system
    - Inoperative or missing catalytic converter
    - Faulty or missing air injection system

    Hi CO at Idle Test

    Excessively rich mixture due to:

    - Miss adjusted idle mixture
    - Dirty air filter, faulty carburetor or choke
    - Faulty computerized engine management and/or Oxygen sensor - Faulty fuel injection
    - High fuel electric fuel pump pressure (fuel regulator fault, restricted return line
    - Inoperative or missing catalytic converter
    - Faulty evaporative canister purge system
     
  2. admin

    admin Administrator Staff Member

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    High NOx on driving Test

    - Inoperative or ineffective EGR (Exhaust Gas Recirculation) system
    - Excessive lean air/fuel ratio
    - Inoperative or missing catalytic converter (three way catalytic)
    - Excessive spark advance
    - Faulty Thermostatic Air Cleaner (TAC) system
    - Defective computerized engine management and/or Oxygen sensor
    - Engine Deposits (Carbon)
    - Engine Mechanical defect(s)

    Some of the most common missed items related to emissions

    - Dirty or contaminated engine oil.
    - Plugged or non-functioning PCV system (Positive Crankcase Ventilation). (Valve or filter)
    - Fuel Filter
    - Air Filter
    - Defective drive belts
    - It could be one or more problem(s)

    [​IMG]
    This is a simplistic EGR valve, there are more complicated system used on vehicles. Its importance is considerable when the whole picture of NOX (Emission) control.

    This valve and controls can and cause mechanics quite a few headaches, when diagnosing engine performance.

    The EGR valve performs its function by allowing exhaust gases back into the intake manifold, diluting the Air/Fuel ratio to reduce NOX by controlling combustion temperatures.

    An EGR, which does not open at all, may not be observed as a problem when it comes to driveability until the spark plugs burn away at a rapid rate. Causing misfires or under severe conditions melts and perhaps cause pistons to overheat and cause premature engine failure.

    An EGR, which does not, close, however is almost always the cause of a driveability complaint in the form of lack of power and rough idle conditions. It usually shows up as a vacuum leak and that one or more cylinders are not performing properly.

    Following is an example of an Emission Inspection Report

    This is only a sample----Failure caused by EGR Valve not opening.

    [​IMG]

    Purpose of Catalytic Converter (CAT)

    Catalytic converter systems lower the amount hydrocarbons (HC), carbon monoxide (CO) and NOx gases in the vehicles emissions by providing an additional area for exhaust gases to oxidize or burn. This is accomplished by using a chemical catalyst to speed up the oxidation and reduction process.

    Operation

    Exhaust gases leave the manifold enters the catalytic converter. Here the gases are directed to flow over the interior pellets covered by the catalytic agents (Platinum and palladium). As this happens, the exhaust gases increase their temperatures and continue to oxidize, removing Hydrocarbon and carbon monoxide emissions from the exhaust before it enters the muffler. The heat developed in the catalytic converters is extremely high; auto manufactures have devised various systems of control and insulation to insure its safe operation.

    [​IMG]

    Your feedback is GREATLY appreciated!! Please post your comments below.
     

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