Emissions Tuning Fundamentals: Standard 5 Gas Analyser

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Standard 5 Gas Analyser

08.21

00:00	The next logical step in terms of emissions equipment is a 5 gas analyser which are generally going to be somewhere in the vicinity of $4000-$9000.
00:08	These are a significant step up from the cost of a wideband O2 sensor but well short of the hundreds of thousands of dollars lab grade emissions systems cost and unlike a wideband sensor, 5 gas analyser can actually measure emissions.
00:23	Rather than measuring just one factor in the potential creation of harmful emissions like a rich or lean mixture or excessive combustion temperature, now we're directly measuring the emissions.
00:34	As you might have guessed, the name 5 gas analyser comes from the 5 gases that these devices commonly measure.
00:41	These are carbon monoxide or CO, carbon dioxide or CO2, hydrocarbons or HC, oxygen or O2 and oxides of nitrogen or NOx.
00:54	CO, CO2 and NOx are usually presented as a percentage of the exhaust sample while hydrocarbons is generally presented in parts per million or ppm for short and O2 is displayed in lambda, just like a standalone wideband would.
01:09	While you technically could use a 5 gas analyser instead of a wideband, widebands often output data at a higher rate and they're cheaper and easier to use and maintain.
01:19	For those reasons, using the wideband for preliminary tuning and then bringing in the 5 gas for fine tuning is the typical approach.
01:26	The next thing of note is that the items that emissions regulators are looking for are all here except CH4 which is methane.
01:34	Generally if you can achieve great results on a 5 gas analyser, you probably won't have a methane issue so these relatively affordable devices can still be very effective.
01:44	A sample can be taken from anywhere in the exhaust system and depending on your project, it may make sense to take readings pre or post catalytic converter.
01:54	Taking a sample post cat is how emissions are generally judged but taking a sample before the cat can give you insight into how much it's cleaning up.
02:03	This information can help you make even larger improvements, taking a sample closer to the engine also has the advantage of reduced transport delay which is the time between a combustion event occurring and the exhaust gas travelling to the analyser and actually being sampled.
02:19	The sensors in a 5 gas system aren't designed to accept exhaust gases at full temperature so whether you're sampling pre cat or near the tailpipe, you need a way to cool things down.
02:30	Welding a small sampling bung to the exhaust connected via a compression fitting in a flared copper sampling tube is a common practice.
02:38	After several feet of copper pipe, you can transition to a clear hose which allows for some observation of contamination and then the connection to the actual 5 gas analyser.
02:47	It's important to check the specs on your particular device to ensure the sample is within the acceptable temperature range.
02:55	The hotter the exhaust is at the sampling point, the longer the copper tube must be in order to cool things down before reaching the 5 gas system.
03:04	Basic 5 gas systems don't control exhaust flow out of the engine so the exhaust travels there passively.
03:10	When operating an engine at high speed and load, the exhaust flow rate will be high and the delay between an engine event and it being sampled will be relatively low.
03:20	On the other hand, if you're testing start up or idle, the time it takes for the gas to reach the sensors can be very long.
03:27	Variable transport delay combined with the relatively low response time of some 5 gas sensors can make tuning transient conditions challenging.
03:36	For example it's not unusual for it to take over 40 seconds for the analyser to output a change from engine off readings.
03:43	In that case you still get to see the data and you can clearly see where the engine starts but you can imagine this gets tricky to line up with engine behaviour once you start driving.
03:53	Speaking of transients, peaks and troughs in readings may also be clipped because sensor response isn't terribly rapid.
04:00	On the plus side, steady state conditions like hot idle aren't impacted by these concerns.
04:05	You can let the vehicle hot idle for a few minutes, look over the results and have a great picture of the idle emissions performance.
04:12	For this reason, 5 gas analysers are sometimes used for government emissions testing of in use vehicles, meaning vehicles that have already been sold and are out in use on the public road.
04:23	That sort of testing may be required to get or renew a valid vehicle inspection or may even be part of a roadside test if you live in an area that has more aggressive end user enforcement.
04:34	Applicable inspection stations use a 5 gas analyser for its reasonable cost and steady state monitoring capability which is suited to what's called a 2 speed idle test.
04:44	This unsurprisingly comprises of readings taken at 2 speeds.
04:48	The engine is tested at warm idle speed and while revving and holding the engine at 2500 RPM or similar.
04:54	Over time as engine and calibration technology has improved, emissions have reduced and current vehicles run so clean that this actually brought to light another shortcoming of the 5 gas analyser.
05:06	Most of the sensor designs are old and were optimised to read emissions in a range well beyond what's normal today.
05:12	In particular, NOx emissions have been reduced massively over the last few decades and now most 5 gas units can't read the very small amounts of NOx that can make or break a passing emissions certification result.
05:25	For example, a 5 gas unit might display 0% NOx despite a small but unacceptable amount by today's standards being produced.
05:34	The carbon monoxide and hydrocarbon sensor range and resolution will be sufficient for some current vehicles but potentially not those in the most stringent emissions categories.
05:43	This is a case where standards will likely continue to become more strict so analyser updates will likely follow suit.
05:49	CO2 reading accuracy on the other hand generally won't have this issue since it's acceptable to create CO2 at higher levels.
05:57	In another module we'll discuss a device that bridges some of these gaps to lab grade equipment but we'll leave it here for now.
06:04	These systems generally require a warm up period before operation.
06:08	Not for the engine but for the 5 gas analyser itself.
06:12	With the vehicle's engine off, you provide the 5 gas unit with power, then wait.
06:16	For somewhat accurate readings, you generally have to wait between 5 and 20 minutes.
06:21	Then to get even more accurate readings to calibrate the system, you may have to wait a few hours.
06:27	In addition to keeping the sampling tube and hoses clean from soot, water and other debris, 5 gas systems require periodic maintenance and recalibration.
06:35	Before purchasing, it's a good idea to ask the supplier about maintenance supplies and costs so they aren't a surprise later.
06:41	Some manufacturers also offer factory maintenance for those not interested in performing it themselves.
06:47	Frequency of maintenance depends on how much you use the equipment, how clean the test environment is, ambient conditions and of course how clean the engines are running.
06:56	If the engine is creating excessive particulate matter before you clean up a calibration, that can clog up an analyser quite quickly.
07:03	This may require service far sooner than the hours on the device may suggest.
07:08	Repeatable units will come with warm up, calibration and maintenance info though each brand and model will be a little different.
07:14	I've given you the gist of what to expect but of course be sure to read and follow manufacturer instructions if you decide to go ahead and purchase your own 5 gas unit.
07:24	After all, if you spend the money on the device but the data is skewed due to a lack of calibration or maintenance, then you're not getting the true value and potential from the tool.
07:33	Let's recap what we've learned about 5 gas analysers.
07:36	While emissions improvements can be made based on data from an OBD scanner, wideband, EGD probe and other inexpensive items, 5 gas analysers are the first level of actual gaseous emissions measurement.
07:48	For a few thousand dollars, you don't get the response time or accuracy of a $200, 000 plus lab grade analyser however with patience and care, you can perform back to back tests, observe results and work towards optimised calibrations.
08:03	Because transfer delay time is so variable and sensor response isn't particularly quick, steady state 5 gas analyser testing is most effective.
08:12	5 gas units need warm up time and should be serviced and recalibrated periodically.