Tuners: Test Your Injectors!

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This leaves the lowly Mineral Spirits as a practical contender for day-to-day testing. The up side is it’s easily obtained locally and it’s less likely to turn your shop into an inferno. The down side is the viscosity is about twice that of the other fluids including gasoline. The specific gravity of Mineral Spirits is also heavier than the other fluids with gasoline about .640, N-Heptane at .683, 40CFR86 at .740, and Mineral Spirits the heavy weight at .780. In the real world of comparative testing, this is easily corrected for by controlling fluid temperatures and using corrective coeffecients on the test results.

 

Tuners: Test Your Injectors!Tuners: Test Your Injectors!Tuners: Test Your Injectors!

Above, are examples of injectors that were purchased from companies that specialize in drilling out stock injectors. Damaged pintle heads, drill burrs in holes not removed; holes which are poorly finished and inconsistent. Flow values off by more than 10% from advertised values and variances as high as 50cc/min within a set are not rare.

 

There will be a slight non-linearity between Mineral Spirits and N-Heptane due to the viscosity difference when comparing flow rates between a single orifice and a multi-orifice injector of the same flow rate. This is due to the additional surface friction of multiple orifices vs. a single orifice of the same total cross sectional area. This isn’t a normal test scenario, but would be a good reason to break out the N-Heptane. Testing static and dynamic flows with both fluids on both types of injectors will give you a good calibration factor for Mineral Spirits vs. N-Heptane.

 

Tuners: Test Your Injectors!Tuners: Test Your Injectors!Tuners: Test Your Injectors!

Damage to the pintle head from using it as a drill stop, causes a significant amount of turbulence at the hole entrances, making repeatable flow tests impossible. Use drilled injectors, in expensive performance engines at your own risk.

 

On the hardware side, you will need a good adjustable 20+ amp. 0-20V power supply to run the pump and injectors, an accurate adjustable timer, an adjustable square wave signal generator with a driver to control the injector, a 2 channel oscilloscope, a DC Inductive Current Probe, and an Accelerometer or you can substitute a Bosch detonation sensor (the type with a hole in the center) to measure closing latency.  Construct a fluid reservoir with a pump, filter and regulator (with a lab quality pressure/temperature gauge or sensor as close to the injector as possible). See section 6 of J1832 for a full test rig description. The preference is to measure flow quantities by weight more so than by volume, so basically you will be starting with a good .1 gram accuracy scale (with a serial port if you want to automate the rig later) with a bucket on it.

 

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