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some injector capacity ratings are given for 80% duty cycle and some for
100% duty cycle, often leading to confusion
The safest thing to do is to measure your particular injectors. Before
doing that, check in the NIRA rk Wizard if your injector type is available as
a “preset” type. If it is, you don’t need to measure things yourself.
In the example below the injector capacity is 400cc/minute at 3 bar pressure
using gasoline.
The density of gasoline from a retail chain such as OKQ8 is 750 kg/m
3
at
15°C. You need to convert these values in order to calculate Injector Gain
because NIRA i7x needs to know the weight of the fuel being injected, not
the volume.
The weight in grams of the fuel depends on:
Fuel density. The density is different for 98 octane gasoline, racing
fuel, E85, ethanol and methanol. Even within a category the density
can be different. As an example, the different racing fuels offered
under the VP brand differ with up to 15%
The temperature of the fuel
If you expect to use a different fuel pressure than the pressure at which the
capacity was determined, an approximation is that the Injector Gain value
changes with the square root of the pressure ratio.
Example:
400 cc at 100% duty cycle and 3-bar pressure
At 4-bar pressure: sqrt(4/3) = 1,155 X 400 = 462 cc
If you use regular retail gas and the temperature of the fuel is 15°C and
the pressure is the same as when the capacity was determined and the
duty cycle is 100%, the formula for Injector Gain is trivial:
Divide 80000 into the number of cc/min. This gives Injector Gain
Example: 80000/400cc = 200 ms/g
The Wizard has additional information on this topic. Enter the value in the
Injector Gain parameter in Engine Setup in NIRA rk.
5.1.4 Engine Setup -> Fuel Specifications
Fuel specifications are used to compensate the amount of fuel based on the
fuel characteristics.
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