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The following article has some good information regarding how testing is performed and the goal of the test (actual flow for real world application, or simply to test for consistency among injectors in a set).
Simply, the testing medium plays an effect on flow capacity.
Quoted from http://www.injectordynamics.com/questionsanswered.html -
2. Why Are Your Injectors Rated at 1000cc/min When They Only Flow 880cc/min on My Flowbench?
This next subject is in response to an internet forum thread and not a response to an email. Although I did get an email asking about the flow rate of the 1000cc injectors, I never responded. Apparently I should have, because it made its way on to the forums with the result being that Tony at T1 was catching hell.
The question was, "why are your injectors rated at 1000cc per minute when they test at 880cc on my bench?" The short answer is that your flowbench uses mineral sprits, or some other "calibrated" test fluid while my flowbench uses gasoline which has approximately half the kinematic viscosity of mineral spirits.
It was proposed that we were being misleading because we were not testing according to "industry standard."
I'm not sure if the question was posed to stir up trouble or simply to get an answer, but it doesn't really matter because it is a valid question.
And here comes a valid answer.
The technology that we call "Injector Dynamics" was developed not from a desire to be part of "the industry" but from a need for accurate injector characterization because it was completely lacking in the industry.
To be more specific, we felt that the fuel injector was the least understood part of a fuel injection system and so we set out to characterize them in much the same way that you would run an engine on the dyno while measuring torque, horsepower, temperatures, pressures, lambda, etc.
We were not looking for a simple test designed to show relative flow differences between injectors, we were looking for a test that would exactly relate dynamic injector characteristics to a running engine.
During the development phase, we worked closely with Motec USA's engineering department, and they offered direction by specifying how the data should be presented. Left to my own devices, the end result would have been streams of engineering data which the end user would then have to sort through.
At this point I should thank Simon Wagner, Head of Engineering at Motec USA for slapping me in the face with a dose of practicality so that my work would be well received and genuinely helpful to his dealers.
Motec requested that the data be interpreted in a manner that would allow their dealers to quickly look at the data, and determine the following; Dead Time Compensation Values, Maximum Horsepower Potential and Useable Operating Range.
For any of these values to be relevant, the test fluid must be the same, or at least very close to the fluid that will actually be powering the engine. The most obvious example is horsepower potential.
The horsepower potential of an injector is determined by considering its dynamic flow rate, and the Brake Specific Fuel Consumption of the engine. Brake Specific Fuel Consumption is a measure of how efficiently an engine turns fuel into horsepower, and is stated as pounds per hour per horsepower. Put more simply, pounds of fuel required per horsepower.
For example, if your engine makes 1000 horsepower, and uses 500 lbs of fuel per hour, it has a brake specific of .5 (500lbs per hour fuel flow divided by 1000 horsepower equals .5)
Using the above example, let's calculate the power potential of an injector using both gasoline and mineral spirits as a test fluid. If we convert the flow numbers from cc/min to lbs per hour we get 95.24 lbs per hour for gasoline, and 83.8 pounds per hour for mineral spirits.
If we divide our brake specific of .5 into our gasoline flow rate of 95.24 we get 190.48 horsepower per injector. Performing the same calculations with mineral spirits we get 167.6 horsepower per injector for a difference of 13.6 percent!
I don't know about you, but in my world an error of 13.6 percent is equivalent to a solid kick in the nads.
To sum all of this up, if the purpose of flow testing is to show relative static flow differences between injectors, mineral spirits, olive oil, or even KY Jelly will get the job done. On the other hand, if the purpose is to relate the data to actual engine performance, the intended fuel must be used.
It should be noted that accurately calculating the horsepower potential of a fuel injector is a bit more complicated than in the above example but in the end, a 13.6% flow error will always equal a 13.6% error in calculated power potential.
In the near future we will post a downloadable horsepower calculator for all of the Injector Dynamics fuel injectors. The horsepower will be calculated based on dynamic flow, dead time, recovery time and BSFC. For those of you testing on an engine dyno where you accurately measure BSFC, you will find that the results are spot on.
PY ---
2012 2500HD LML
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