FUEL FLOW RATE and FUEL MANAGER Functions

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jimh
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FUEL FLOW RATE and FUEL MANAGER Functions

Postby jimh » Thu Apr 02, 2020 4:27 am

FUEL FLOW RATE

With E-TEC engines, there is no need to install an in-line flow monitor device in the fuel line feeding the engine in order to obtain engine fuel flow rate data. The E-TEC engine already is sending this data--and sending more accurate data than an in-line flow sensor could send--to the NMEA-2000 network via the EMM connection to the network.

Modern engines routinely send their rate of fuel consumption as part of their engine parameters, sent in the NMEA-2000 parameter group number PGN 127489: Engine Parameters, Dynamic. For more information see

NMEA-2000 Parameter Groups
http://continuouswave.com/whaler/reference/PGN.html

Note that the E-TEC only sends the instantaneous rate of flow. If you want to convert the rate of flow over time, that is, integrate flow rate into a volume, you will need a device with a FUEL MANAGER that can perform that calculation. The E-TEC engine only sends rate of flow, and it does not attempt to track total volume of fuel used.

FUEL USED, FUEL REMAINING, TANK LEVEL

As mentioned above, the FUEL MANAGER function computes a value for FUEL USED by integration of fuel flow rate over time. This value can then be used to calculate FUEL REMAINING in the fuel tank, based on the operator entering data into the FUEL MANAGER about the volume of fuel added to the tank at each refueling. From an initial operator-entered value of FUEL REMAINING (which in some cases must be a full-tank, see below) the FUEL MANAGER will deduct the volume of fuel it calculates as FUEL USED from integration of flow rate over time, and add to the volume of fuel in the tank the amount the operator manually enters as data at each re-fueling.

The FUEL MANAGER function can also provide a TANK LEVEL calculated value, based on a TANK VOLUME that the operator has entered during configuration. The tank level is just a calculation based on the fixed value TANK CAPACITY and the calculated value FUEL REMAINING. This is an indirect measurement of tank level, as opposed to a direct measurement of tank level using some type of tank level sender. For more see

FUEL TANK LEVEL MEASUREMENT
http://continuouswave.com/whaler/refere ... Level.html

With tracking of FUEL REMAINING by a FUEL MANAGER with the indirect method, a general problem is the possibility for error due to errors made by the operator in entering data about fuel added. If the operator forgets to enter data about fuel added, the FUEL REMAINING and associated calculated TANK LEVEL values will be in error. Also, if the operator does enter data at refueling but enters the wrong volume, only errors with entering data that are less than actual can be corrected. (You repeat the input process and add more fuel as a correction.) If an error is made by entering too much fuel added, most FUEL MANAGER functions do not allow for a subtracting correction. To get the FUEL MANAGER back on track if this sort of mistake is made, the operator must make note of the error and on the next refueling input a value for fuel added that corrects the error, that is a value entered that is less than the actual volume by the amount of the prior error. (It is inevitable that an error like this will occur, as I can attest from my own experience. If you accidentally enter, say, 10-gallons too much fuel added into the FUEL MANAGER, you have to make a note to enter 10-gallons less than actual on the next refueling to get the FUEL MANAGER back to an accurate calculated value.)

Also, some FUEL MANAGER functions will expect that the initial value of FUEL REMAINING must be the 100-percent value of TANK CAPACITY, that is, they will set the tank level to be FULL at initialization. This can also be a source of error if the actual tank fuel volume was not at full-tank level when the FUEL MANAGER was initialized.

If the operator is diligent and correctly inputs data about fuel added, the calculated values of FUEL REMAINING and the related calculated value of TANK LEVEL will be very accurate.

Also note that it is quite possible that more than one device connected to a NMEA-2000 network will offer to provide a FUEL MANAGER function. As an example, on my own boat I have two devices that track fuel. The ICON Pro RPM gauge has a FUEL MANAGER, and so does my chart plotter/SONAR, a Lowrance HDS. These two devices each separately compute FUEL REMAINING from the same data from the engine. These calculated values of FUEL USED or FUEL REMAINING or TANK LEVEL will not be precisely identical, but generally will be in close agreement. (Since I still have an actual mechanical tank level indicating gauge, I can compare the TANK LEVEL among all three to see how closely they match.)

It may also be possible on some FUEL MANAGER devices to switch the data source for FUEL REMAINING to come from a tank level sensor. This reverses the calculation process, and FUEL REMAINING is calculated from TANK LEVEL data from a sensor and a value for TANK CAPACITY entered at initialization. Generally the accuracy of this method of deducing FUEL REMAINING will only be as accurate as the calibration of the tank level sensor to the fuel tank geometry. Changes in the trim on the boat can also affect the calibration.