In Part 1
we discussed the emission test. In Part 2, we will be discussing the results of the test. As we discussed earlier the amount of emissions allowed varies on the year of the vehicle. We need to keep our vehicles in good shape to reduce the amount of emissions released into the environment.
In our engines we combine HC (Hydrocarbon fuels) and air (78% Nitrogen and 18% Oxygen). Ignited by a spark, the fuel combines the chemicals in the cylinder. If everything burns completely we have; H2O (Water), CO2 (CarbonDioxide) and N (Nitrogen) as exhaust emissions. Note that none of these emissions are part of the emission failure. Unfortunately our engines do not burn the fuel perfectly. Many factors will affect the cylinder efficiencies, including fuel systems, cylinder designs, engine temperatures and emission controls.
Next we will go thru the causes of the emissions that could cause a failure on the test. Air fuel mixture is extremely important to combustion efficiency. A RICH mixture means the Air and Fuel ration has more fuel than it is supposed to. Typically on our cars we shoot for approximately a 14.7 to 1 air to fuel ratio. This means we have 14.7 parts air to 1 part gasoline by weight. A rich mixture would be less air or a 10 to 1 air/ fuel ratio. A LEAN mixture would be more air an 18 to 1 air/fuel ratio.
CO – carbon monoxide: This poison gas is produced in a chemical reaction during the burning process of Hydrocarbon fuels. This is from fuel burning with a low oxygen content. An example would be charcoal grills being used in a closed area. We have all heard the horror stories of people dying from carbon monoxide poisoning. The fuel used up the oxygen and combined the carbon in the fuel with 1 oxygen molecule. If the fuel had burned properly it would have produced CO2(Carbon Dioxide) as an indication of complete combustion. The usual cause is a rich mixture in the cylinder which caused an incomplete combustion, because the fire burned out. Rich mixtures can be caused by a problem with the fuel system, a restricted air intake (Dirty Air Filter) or an engine mechanical problem (Low Compression).
HC – hydrocarbons: Hydrocarbons are raw fuel. Whenever a vehicle has high hydrocarbons we should ask ourselves, “how did raw(unburned) fuel make it thru our engine”. Typically it is because 1 or more cylinders have misfired. This can be an ignition problem or a mechanical problem. Another source of a misfire would be an extreme air to fuel ratio, either rich or lean causing a misfire. Another source of HC is fuel vaporizing. This is why we now have sealed fuel systems that hold pressure. This is the reason for the fuel cap and tank test.
NOX – Oxides of nitrogen: Oxygen and nitrogen do not readily combine. Under very high cylinder temperatures and pressures usually above 2200°F, they can combine. NOX produces Photochemical SMOG. Today’s vehicles run very high cylinder temperatures to reduce CO and HC emissions. Unfortunately this increases NOX.
Part 3 in this series, will discuss the systems on our vehicle that are designed to reduce the harmful emissions.
Part 4 in the series, will discuss some diagnostic steps you can take to try to remedy a failed test.