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Diesel Tuning Fundamentals: Smoke Limit

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Smoke Limit

02.42

00:00 - As we've discussed so far in the course, there is a practical limit as to how much fuel we can inject for a given mass of air before we start producing soot deposits that become apparent as black smoke emitted from the exhaust system.
00:13 While we've probably all seen diesel tractor pull competitors or drag racing competitors blocking out the sun thanks to huge plumes of black smoke from their exhaust during a pull, this is obviously highly undesirable from an OE perspective and significant effort goes into producing clean tail pipe emissions.
00:33 Often this is achieved thanks to a table in the ECU that limits the volume of fuel that will be delivered based on air mass and engine speed, and this is often referred to as a smoke limit table.
00:44 An alternative way of achieving a similar aim is to use an air fuel ratio or lambda limit table to define the richest air fuel ratio that the ECU is allowed to command based on air mass and RPM.
00:58 With an air fuel ratio limit table, the ECU is typically going to be calculating the expected air fuel ratio based on air mass and fuel volume rather than actually measuring this with an air fuel ratio sensor in the exhaust.
01:12 A key point to take away from this module is that if you're reflashing a stock ECU, it's possible that these smoke limit tables may be overly conservative and limit the amount of fuel that's being provided.
01:24 If you're not aware that this is happening it's possible that you may struggle to increase the fuel delivery over stock as the smoke limit tables will be simply undoing all of the work that you're doing in the main fuel delivery tables.
01:36 I'm not advocating that you eliminate the smoke limit tables or set these to a maximum value to render them ineffective however there is often a significant difference between what we're trying to achieve in the aftermarket compared to an OE manufacturer, who must put emissions compliance above every other aspect of the diesel engine's performance.
01:57 Exhaust smoke will be obvious to the eye when it becomes excessive, however the output can be quantified and measured through the use of a smoke meter or opacity meter as they're also known.
02:09 These meters measure the amount of light blocked by the smoke in the diesel exhaust and output the smoke density.
02:16 If you have access to an opacity meter, they can make tuning the smoke limit table and in fact the fuel delivery in general, much more accurate and faster.