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Old 11-17-2012, 11:12 AM
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Flyingman Flyingman is offline
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Originally Posted by floydarogers View Post
No. The ST810 and Intro to diesel tech docs that have been posted here make it clear that they use an active NOx sensor to drive the amount. Remember, there are actually two catalysts: the one in the DPF (which reduces NO--> NO2), and the SCR (which completes the reduction to NOx --> N2 + O2)
Agreed, it is monitored by NOx sensors, but translates to about the same ratio of fuel consumed to DEF used. i.e. you should get about 13,000 miles between refills, but as we have all seen this can vary. It seems easy enough to add some DEF so shouldn't be such a major issue. About same as adding window washer fluid, no?

Q. How can an operator determine how much DEF they will need/use?
A. DEF consumption will be approximately 2% of the diesel fuel consumed. Another way to consider it is that DEF will be consumed on a 50 to 1 ratio with diesel. (For every 50 gallons of diesel fuel burned, you will use 1 gallon of DEF). If you know the average fuel consumption of a vehicle, you can easily calculate the amount of DEF that will be used.
Annual miles for average truck = 50,000 miles
MPG for average truck = 8 mpg
50,000 miles / 8 mpg = 6,250 gallons diesel fuel per year
DEF usage @ 2% of fuel consumption = 125 gallons of DEF / year
125 gallons / 10 gallon tank (average size) = 13 DEF fill-ups / year
Example…..Heavy duty
Annual Miles per VehicleAnnual Total MilesAverage MPG per TruckAverage DEF Tank Size (on vehicle)Annual Fuel Usage (gallons) Consumption per Gallon of fuelEstimated Annual DEF Consumption DEF Fill-Ups per Year 120,000 120,000 6 20 20,000 2% 400 20

Q. Is the DEF dose rate the same for all engine manufacturers?
A. The DEF dose rate will vary slightly amongst engine manufacturers. While most engines will have a dose rate of 2% of diesel fuel consumed, the dose rate will range from 1% to 3%.

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Last edited by Flyingman; 11-17-2012 at 11:17 AM.
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