Quote:
Originally Posted by skyship007
Many Volvo diesels are fitted with EGR valves designed to cut Nox emissions that are real health risk factors. The engines ECU warm up program is designed with the EGR functioning, if it fails or some twit deletes it (New MOT failure point), the engine takes longer to warm up and it is the period the mixture is richer than normal that causes the most in cylinder deposits. If the engine was designed with an EGR present they do not increase wear rates but reduce them!
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Serious? the mixture is richer during warmup (without egr) in diesels ?
Its the other way arround
Without egr the air to fuel ratio is (way)higher wich means leaner and hotter wich creates the nox in the first place :heat!
The purpose of egr is to cool combustion down (and replace the part of oxygen & nitrogen with an inert (exhaust)gas that isnt needed for combustion (in part engineload) with fuel but can react due to heat with eachother ) in part engineload to prevent nox from forming
The reason the engine warms up faster in modern diesels with egr has nothing to do with the (cooler) Combustion itsself but with the mandatory egrcoolers wich extract egr heat directly from the exhaustgasses into the coolant
So blocking the egr means also no hot exhaustflow trough the egrcooler and no extra heat into the coolant
One reason that wearrates could go down with a diesel with egr compared to a blocked one can be to the fact that more carbon particulates dissolved in oil can act if they are squashed in the engine as a "graphite" (not so much to the point the oil cant suspend it anymore ofcourse)
ps
Quote:
Originally Posted by skyship007
the engine takes longer to warm up and it is the period the mixture is richer than normal that causes the most in cylinder deposits.
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Air to fuel ratios in diesels have completely different meanings compared to (indirect injected)gasoline engines (the only engines wich use fuelenrichment during warmup) , if nox played no role diesels were running extremely lean as in the old days in part load 60 to 1 also during warmup
The reason a gasoline engine runs rich during warmup has nothing to do with emmissions but is required to let the engine run in the first place because too much fuel will condens on cold cilinder walls wich prevent proper combustion and needs to be compensated for with extra fuel to leave enough gasoline in gasform to combust with lamda 1
Thats why direct injection gasoline engines dont need fuel enrichment anymore because the fuel is injected at the end of compression almost like a diesel and cant condens at the cilinder walls
In dieselengines egr increases fuelconsumption but egr in gasoline engines decreases fuelconsumption because in part load the partly closed throtlle will create underpressure/pumpinglosses wich the egrflow behind the throtlle will equelize