Atmospheric Correction

Because barometric pressure, air temperature, and humidity have a direct effect on the power output of internal combustion engines, it is vital that you consider weather conditions during dynamometer testing. Otherwise a 1% improvement (from modifications) gets lost within a 2% swing from a significant weather change.

Power testing should be done under nearly identical atmospheric conditions, but that’s not always feasible. Instead, correction factors (multipliers) help us estimate what that engine’s power is (probably) under baseline test conditions. Older analog dynamometers required doing this math with a pencil, but the DYNOmite data-acquisition computer does the math for you (you just manually enter in the weather information). An optional DYNOmite Weather Station module (shown above) goes even

Customer Spotlight

Segway, LLC

TM

Chassis dyno testing a SegwayHT with Land & Sea’s DYNOmite (above)? You bet! It’s sort of like a treadmill for human transporters. In 2000, inventor Dean Kamen needed to simulate a multitude of real world loads on what is arguably the most revolutionary transportation development in decades. His torture-testing program also had to be hidden from the public eye, since “Ginger” (the project’s code name) had yet to be officially acknowledged.

When DEKA Research & Development ordered their first DYNOmite Eddy Current Kart Chassis Dynamometer, they even took the precaution of telling Land & Sea they were doing “electric wheelchair” testing!

Now that Segway HTs are finally available to the public, Land & Sea is working with Segway on developing custom DYNO-MAX “Pro” simulation control routines.

One possibility is to modify the DYNOmite Electronic Throttle Control to instead simulate the slight leaning the Segway operator normally uses to control speed. This configuration should allow DYNO-MAX’s Automated Test mode to simulate both the operator’s input and the terrain.

As Segway HTs inevitably spread across the globe, it is possible that these dynamometers will be used outside the research lab… possibly for service and operator training. Who knows, once NASCAR teams latch onto using Segway HTs to get around the pits, they’ll just have to dyno them!

2003 -PO Box 96 North Salem, NH 03073 (603) 329-5645 www.land-and-sea.com

further by automatically collecting the cell’s atmospheric conditions, in real time. This is the best method as you are always correcting with the right pressure, temperature, and humidity data.

Several atmospheric correction factor standards exist, but most vary primarily by what they use as reference points. For example: “Standard” SAE J607 factors are popular with hot-rodders (and snowmobilers) because they are based on “engine friendly” conditions of 60 degrees Fahrenheit air temperature (cool), 29.92 Inches of Mercury barometric pressure (sea level), and 0% relative humidity (dry air). Like all correction factors, SAE J607 tries to predict how Mother Nature is influencing the power of your test engine. But, like all estimations, the bigger the guess — the more room for error.

Consider an engine run on a hot muggy day in 5000’ elevation Denver, Colorado gains 25% applying the Standard factors! Unfortunately, verification tests prove that such large corrections (estimations) are unreliable for quoting absolute power. Even the newer SAE J1349 factors (based on 29.38” and 77 degrees), still return a shaky 20% adjustment! Ethical high altitude shops only use large factors for relative comparisons between engines tested at the same altitude.

If you require certifiable power data, even when Mother Nature will not supply you with near “standard” conditions, you must modify the test cell’s atmosphere. For our high altitude example, that requires a dyno room pressurized by large (expensive) blowers and drawing air from either a pre-conditioned warehouse or very high capacity air conditioners. Smaller shops just wait for the weather to change!

Cloning On-Board Tests

You can use DYNO-MAX “Pro” to create dyno simulations from on-vehicle data recordings. This information can be obtained from your DYNOmite Data Computer or many third-party engine management and data-acquisition system’s test files. Perhaps you have already recorded some track data with an on-board data recorder. If you output that recording in a compatible file format, DYNO-MAX can then read, convert, and save it as an Automated Test Run (.ato file). This is often easier than creating every line of a complex simulation from scratch.

Your recorded vehicle data must include engine rpm (or road speed) along with elapsed time (in decimal seconds). If that file also includes torque (or throttle position), DYNO-MAX can use that additional information to control an electronic throttle during dynamometer operation.

DYNO-MAX “Pro” reads data from either ASCII Comma Separated Values (.csv) format files or its own (.run/.raw) files. The Auto Test Set Up Wizard provides a “Clone Run Test” tab where you can browse for the specific file to clone and, optionally, define the column layouts like this sample (1second duration) ASCII file:

While native DYNO-MAX .run files are always in the required format, for .csv files you specify which columns contain what data.

What if your third-party data-acquisition system does not store data directly in the required format? Fortunately, most systems can at least save data in a file type that is readable via programs like Microsoft’s Excel. Within a spreadsheet it is easy to reformat columns (like an incompatible time structures) into the above layout. You then save (or export) that spreadsheet back out as a .csv file, ready for DYNO-MAX to Clone an Automated Test from it.

During actual dynamometer testing, DYNO-MAX reads each line of its “Cloned” .ato file, in real time. It interprets the data and instructs the DYNOmite’s servo control(s) to duplicate the recorded vehicle’s behavior. Of course, you can further modify the Automated Test file any way you like using DYNO-MAX’s “Customize Automated Test” tab.

Eddy Current Absorbers

Eddy current dynos offer very fast load control, moderate inertia, and high specific load capacity, especially in the lower RPM working ranges of most industrial type engines. For applications that do not require stall speed loading, an air-cooled eddy current absorber is usually the most cost effective electric absorber you can buy. Since they feature self cooled rotors, no external water supply or resistor bank is required. They also cost less than planetary-driven water brakes and allow far more design flexibility than hydraulic pumps.

Many people associate eddy current absorber only with larger applications. However, our "Micro" Eddy Current Dynamometer is ideal for small engines up to 1 Hp including those in model airplanes and R/C cars. For these 40,000+ RPM application we developed a micro load cell that can read torque changes down to 0.0001 foot pounds.

A slightly larger "Mini" Eddy Current Dyno is suitable for small weed cutter or chain saw class engines. These eddy current systems are ideally suited to emissions and endurance testing of OEM industrial applications as well as ¼ scale Radio Control racing projects.

Absorber sizes continue on up into the 500 Hp range. For still larger applications it is possible to tandem mount absorbers, taking you up beyond 1,000 Hp capacity. So, if you need control beyond what is available from water brake absorbers, give some thought to eddy current units.

2003 -PO Box 96 North Salem, NH 03073 (603) 329-5645 www.land-and-sea.com

PO Box 96 North Salem, NH 03073

PRSRT STD

U.S. Postage

PAID

Manchester, NHPermit # 193

Contact Us

Land & Sea, Inc.PO Box 96North Salem, NH 03073(603) 329-5645

www.land-and-sea.com

^� 2003 -PO Box 96 North Salem, NH 03073 (603) 329-5645 www.land-and-sea.com