5 - G A S A N A LY Z E R
WHAT IS INFRA RED MEASUREMENT? Infra red light is directed through the sample gas in the sample chamber and the amount of light passing through the sample is measured by the detector — 3 detectors used for HHGA5C • Carbon Monoxide (CO) 0-5% • Carbon Dioxide (CO2) 0-15% • Hydrocarbons (HC) 0-2000ppm Industry standard Accurate Fast Replacement not usually required
GAS IN
GAS OUT DETECTOR
IR LAMP
OPTICAL FILTER
Fig. 2
for a five gas measurement. The exhaust gas stream goes into the inlet part of the detector and then an infrared light beam is shot through the gas sample which is bounced off of and optic fi lter. Then the gas sample will exit the detector. The three gases that the detector focuses on are carbon monoxide, carbon dioxide and hydrocarbons. (Fig 2) Nitrous Oxide or NOx and Oxygen O2 are also tested as well. The deadliest or most harmful of the five gases is Carbon Monoxide or CO. A major component of polluted air, CO is a colorless, odorless gas which, when concentrated, is toxic. Any fueled engine properly adjusted and in good operating condition produces relatively low CO readings. Excessive CO develops when the combustion chamber is receiving a large volume of fuel and a proportionately small amount of air. By weight, carbon monoxide
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Fig. 2: This image depicts how a diffuser on a 5-gas analyzer works. Infrared light is directed through the sample gas and the amount of light passing through the sample is measured by the detector.
accounts for about 47% of air pollution produced by vehicle emissions. Think about a cylinder misfi ring that has lost its spark, and all that extra unburned fuel exiting out the cylinder into the catalytic convertor then out the tailpipe. Does a flashing check engine light signaling a catalytic convertor damage warning come to mind? The CO reading on your analyzer will be extremely high. (Fig 3) Normal CO readings will be 0.5% or less. A five gas analyzer will catch a CO problem before it gets too bad. It may or may not see the problem before your scan tool will. This is just one example of the benefits a five gas analyzer will have in your diagnostic testing. But why test the engine for how clean it’s running? Have you ever seen pictures of the skyline over Beijing China? That haze you saw is smog. There was a great concern of having the Olympics there because of that. So what actually is smog? Smog was found to be the result of a chemical reaction that occurs in sunlight between hydrocarbons (HC) and oxides of nitrogen (NOx ). Once the government understood the contribution of vehicle emissions to air pollution, it formulated legislation to control it and that’s why we have strict vehicle emissions standards today. Let’s take a look at the comparisons of a rich and lean running engine from a five gas analyzer and compare it to the scan tool readings. Notice the CO reading on the analyzer is showing an abnormally high reading. (again, see Fig 3) The system is showing a rich condition. The Oxygen sensor reading from the scan tool is showing a high voltage reading indicating a rich condition. This was done by injecting a propane sample into the intake system to see the reaction of both the five gas analyzer and the scan tool. The scan tool picked up the rich fuel sample before the five gas did due to the location of the oxygen sensors located upstream from the five gases probe that is located in the tailpipe. It usually takes a few seconds for the enriched sample to reach the five gas probe. This is normal, due to the distance the sample has to travel. Notice the Lambda reading on the analyzer. It is showing a reading of 903. Lambda is an indicator of the air fuel mixture in the engine. A perfect Lambda reading is at one. Anything less than one indicates there is more fuel in the mixture than there is oxygen. Anything higher than one indicates there is more air than
ASP | JUNE 2021
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