Emissions Tuning Fundamentals: Additional Onboard Emissions Devices

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Additional Onboard Emissions Devices

06.58

00:00	The first widespread emissions control device was the positive crankcase ventilation system or PCV for short.
00:06	Rather than venting the crankcase gases to the atmosphere, the PCV system sucks them into the intake track or intake manifold so that they can be burned in the combustion chamber.
00:16	Later, evaporative emissions systems or EVAP for short were added to contain fuel vapours which were previously vented to the atmosphere as well.
00:24	A charcoal canister stores the vapour and it's then purged into the intake track where it travels to the combustion chamber and gets burned.
00:32	These systems are present on gasoline and diesel vehicles but since gas is more volatile, it's more likely to vaporise.
00:38	Many modern ECUs are able to estimate the amount of fuel that the EVAP system is supplying and shorten the injector pulse width accordingly in order to avoid overfuelling.
00:48	Depending on the vehicle type and which regulatory bodies you're working to satisfy, EVAP performance may have to match the original specifications even if the system has aged to 100, 000 miles.
01:00	In these cases you don't get the benefit of a tolerated deterioration factor being applied to your emissions test results.
01:07	If you're altering a fuel or a PCV system, be sure all components used won't allow any significant permeation of vapours.
01:15	This is crucial in maintaining the integrity of the sealed system.
01:19	Next, we'll discuss secondary air injection which was introduced to provide oxygen to help complete combustion of hydrocarbons in the exhaust.
01:26	The focus shifted to providing additional oxygen to the catalytic converters to assist them in more completely catalysing engine emissions in the first several seconds after a cold start.
01:38	This also helps the cat generate more heat which gets it into its efficient operating range more quickly.
01:44	Later air injection systems utilising pumps are only used during cold engine startup.
01:49	Exhaust gas recirculation or EGR for short is another tool found on gas and diesel engines to help complete combustion of unburned hydrocarbons.
01:59	By running exhaust byproducts back through the engine, there's a second opportunity for combustion, leaving the cats less to clean up.
02:06	Modern engines don't leave a significant amount of hydrocarbons unburned during light load operation though so later engines tend to use EGR more for reduction of NOx output.
02:17	By introducing exhaust into the intake, the combustion chamber ends up with less oxygen available and combustion temperatures therefore drop.
02:25	Avoiding high combustion chamber temperature avoids creating oxides of nitrogen.
02:30	Sometimes EGR is also used to help an engine warm up more quickly to get it into an operating range where the engine is more efficient.
02:38	While EGR may cool the combustion temperature, it heats the intake ports and the cylinder head, aiding in vaporisation of fuel and warming the oil and water as well.
02:48	Particulate filters have been widely used on diesels since around 2010 and they've also become more common on gas engines due to the proliferation of direct injection.
02:59	Whether it's diesel or gas, high pressure direct injection works great in many ways but it does increase the creation of particulate matter.
03:07	Gas particulate filters are abbreviated as GPFs however these are also referred to as autoparticulate filters or OPFs for short.
03:16	In the diesel world we have diesel particulate filters or DPFs but regardless of the fuel, these filters collect particles, then burn them when optimal conditions are present until they no longer present a health hazard.
03:29	This process is referred to as regeneration or regen for short.
03:33	Because sufficient temperature is required for regeneration, particulate filters generally can't operate at idle.
03:40	The heat requirement can be troublesome because stop and go driving tends to generate more particulate matter than steady state cruising without creating the sustained heat necessary to burn off the particulate that's filling up the filters.
03:53	This can lead to a situation where the vehicle presents a warning demanding that the driver cruise the vehicle at constant speed to build heat and facilitate filter regeneration.
04:03	For some whose daily drive involves lots of highway cruising, this may not be a concern but for others it can be a big hassle.
04:11	While certain driving behaviour may create enough heat for what's called passive regeneration, sometimes additional heat is required.
04:19	During an active regeneration cycle, the engine's control system alters operation to purposely create more heat.
04:25	That can mean using less EGR to cool combustion or on a diesel, a richer mixture may be used to increase exhaust gas temperatures.
04:33	We won't dive too deep here because the key is to have a basic understanding of what these systems do and what they need to function properly.
04:42	Lastly I'll touch on something diesel specific called diesel exhaust fluid or DEF for short.
04:49	DEF does the job that the 3 way cats do on gas vehicles by reducing NOx emissions.
04:55	It gets used in a process called SCR which stands for Selective Catalyst Reduction.
05:01	Just like 3 way cats, the end results of NOx treatment are nitrogen and water.
05:06	DEF is generally composed of urea and water but some SCR systems use ammonia for the same purpose.
05:13	Again, you don't have to fully understand the chemistry involved but if a vehicle requires DEF, make sure that it doesn't run out.
05:20	And that brings us to the maintenance of these various systems.
05:24	Replace hoses if they're aged, starting to dry rot, swollen, worn or otherwise appear that they might leak.
05:31	Replace the PCV valve if it's meant to be replaced.
05:34	Years ago, PCV valves were cheap and often easy to replace and you were supposed to do so every few years but recently, as regulators have become more strict, manufacturers have been asked to make all emissions components including PCV valves have longer lifespans.
05:50	Next, EGR systems can get gummed up as oil vapours cause combustion byproducts to stick to the surfaces.
05:56	This happens slowly over time but eventually cleaning the system out may be required to keep it functioning properly.
06:02	Other than that, emissions systems should throw a check engine code if there's a significant issue and the factory service manual should help you resolve it.
06:10	Let's recap the various onboard emissions systems discussed in this module.
06:14	PCV and EVAP systems manage vapours that older vehicles used to vent to atmosphere.
06:20	Air pumps are used to help warm up catalysts for a period of time after cold engines start.
06:25	EGR can help warm a cold engine or cool combustion to reduce NOx output.
06:30	Particulate filters are found on some modern gas and diesel engines with the commonality being direct injection.
06:37	Regeneration requires significant heat so it can only be performed under certain driving conditions.
06:43	To break NOx or oxides of nitrogen up into nitrogen and water, modern gas engines use three way cats and diesels use SCR with diesel exhaust fluid.