Fuel Measurement in Stationary and Vehicle Systems

Max Machinery Recommends the Use of a Single Meter Fuel Measurement System

Max recommends the use of a single meter fuel measurement system to achieve the highest possible fuel measurement accuracy.  Using a two meter system and placing a flow meter in both the fuel supply and return lines and calculating the difference, an “A minus B” system, creates important disadvantages.

A two meter system risks resolution error: i.e. With a 0.5% meter error in a 100 gph supply and a 0.5% meter error in a 95 gph return, you risk a 19% error in measuring the actual 5 gph consumption.  The two meter system must have temperature compensation, even for volumetric measurements, since hot return fuel will expand and over-report the return flow.  Any bubbles that occur in the engine will also cause the meter to over-report the return line flow.  To avoid these issues, a single meter system with a split flow loop is used.


How to Measure with One Meter?
With a high return line volume system as described above, a secondary system must be built that allows the fuel to act as if it is not being measured.  Pressure differences, temperature differences, entrained gases are all to be avoided.  To address these concerns, the fuel measurement secondary system will include a Max Flow Meter, a Max Level Controller, a heat exchanger, a vapor eliminator, pressure regulators and a transfer and/or secondary pump.  See diagram above for more details.  The level controller creates two separate fuel flow loops in the car from the original supply line and return line.  Now, the only connection between the supply and return loops is the fuel being measured by the Max Flow Meter.


The engine loop passes the unused fuel in the former engine return line through a heat exchanger, back to the level controller to be used on the supply side of the engine.  The fuel in the tank supply line is used to cool the heat exchanger and also passes through a vapor eliminator on its way to be measured by the Max Flow Meter as the input to the level controller. The vapor eliminator ensures that only liquid enters the Max Flow Meter as it collects the entrained bubbles and lifts them out of the fluid stream. By measuring only the make-up fuel being supplied to the Max Level Controller, you are effectively only measuring fuel being consumed by the engine via the single meter method. You now have a system that measures 0.5% accuracy or better and has no impact on fuel system performance.


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