SuperFlow AutoDyn, Руководство оператора

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General Testing Information
Volume 3, 9/10/04
Appendix A - Page 201
After 3 seconds, continue to record data rapidly and increase the engine speed rapidly by
advancing the engine speed control knob upward approximately 500 rpm. Let the engine run
another 10 seconds at this point while you continue to record data manually as rapidly as you can.
If you view this set of test data, you will see the actual air and fuel flow delivery readings: first at
3000 rpm and then at the higher test speed. By comparing the data changes over time, you can
determine how long it takes to reach a stable reading. Also examine the power. Power will stabilize
sooner than the fuel flow due to delays in fuel flow measurement.
This test should be the worst possible combination because you are making the most rapid step
change possible. You will probably discover that it requires 5 to 7 seconds to reach a stable data
point.
Production engines experience this problem to a lesser degree because of increased manifold
heat and the higher vapor pressure of typical pump gasoline. The extra manifold heat evaporates
the wall flow back into the air stream and also promotes vaporization of the droplets of fuel and the
spray flow. Unfortunately, manifold heat also increases the temperature of the air charge and
reduces the volumetric efficiency at maximum power.
A.3 Air Flow Measurement
The SuperFlow air flow turbines used to measure air consumption of the engine on your dyno can
provide some very valuable information when evaluating the engine’s characteristics.
Given the importance of air flow, you are missing some critical information if you do not measure
air flow. Volumetric efficiency, air flow, air/fuel ratio and brake specific air consumption become
critical missing links in your engine test program.
The air flow turbine fan spins at a speed that is directly proportional to the volume flow rate.
SuperFlow air turbines are calibrated at 6 test points by comparison to standard orifices. This test
is actually performed on a flowbench, but the flowbench only compares the air turbine readings to
the standard orifice flows. A special mathematical formula correlates the orifice flow reading in
CFM to the air flow turbine frequency. The six flow orifice test data points are entered into the
WinDyn computer program.
The air flow volume is measured and transmitted to the data acquisition system. The data is
processed and calculated with the local barometer, vapor pressure and carburetor air temperature
to provide the displayed data in Standard Cubic Feet Per Minute (SCFM) (Normalized liter per
second or Nl/s). SCFM is what the air flow would be if the atmospheric conditions were measured
at reference conditions, e.g. a barometric pressure of 29.92 inches of mercury, 60 degrees F, and
no water in the air (dry vapor pressure).
As a rule, an engine will consume approximately 1.25 SCFM of air per horsepower (0.8 l/s per kW)
at peak torque while using approximately 1.4 SCFM (0.9 l/s) at peak power.
Look at the Volumetric Efficiency (VE) and the Brake Specific Air Consumption (BSAC) columns. If
the VE percent is very high (>100%) and the BSAC is substantial (>6.0 lbs/HPhr or 3700 g/kWh),
there is a good indication that some of the air and fuel that could have helped to make more power
went right through the engine and was wasted. You should therefore check for a poor valve sealing
or faulty camshaft design.