Sensor Technology Drives Diesel Engine Test Accuracy

Today's diesel engines must meet increasingly stringent environmental requirements while satisfying performance demands of original equipment manufacturers and end-users. To guarantee top engine performance under a full range of operating conditions and to ensure overall engine reliability and conformance, diesel engine-manufacturers must have access to complete test facilities.

09/01/2002


KEY WORDS

 

  • Process control and instrumentation

  • Pressure sensing

  • Data acquisition

Today's diesel engines must meet increasingly stringent environmental requirements while satisfying performance demands of original equipment manufacturers and end-users. To guarantee top engine performance under a full range of operating conditions and to ensure overall engine reliability and conformance, diesel engine-manufacturers must have access to complete test facilities.

To meet these demands, Power Test Inc. (Menomonee Falls, WI) provides a turnkey engine testing solution for commercial manufacturers, and government and military testing applications. Power Test manufactures dynamometers for the diesel industry, including engine and chassis dynamometers and compatible data acquisition systems.

A dynamometer applies a load to a running engine, allowing engineers to determine the engine's running characteristics, such as torque and horsepower, over its operating range. Such testing provides data for performance analysis and component/life-cycle testing. These tests also can determine conformance with environmental regulations over real-life operating conditions.

Inside the dynamometer

In Power Test's dynamometer, water flow, proportional to the desired applied load, creates resistance to the engine output. A controlled water flow through the inlet manifold is directed at the center of the rotor in each absorption section. This water is then expelled to the outer dynamometer body by centrifugal force. As water is directed outward, it is accelerated into pockets on the stationary stator plates where it is decelerated. Continual acceleration and deceleration causes the dynamometer to absorb the power produced by the engine. During this transfer of energy, water is heated and discharged.

The system is comprised of two units, called Commander and Workstation, connected by an Ethernet cable. Commander, a desktop computer operated by Microsoft Windows-based software, issues commands to Workstation, a touchscreen-operated unit housed in a rugged industrial enclosure. Workstation operates the precision load and throttle control systems, collects data, and sends it to Commander to be processed, stored, and analyzed.

Workstation relies on the data acquisition system's accuracy, which depends on ability to correctly measure data in the dynamometer tests.

Pressure sensors measure airflow in the intake manifold, oil pressure, and fuel pressure. Power Test's project engineer Allen Bergst explains that test operators want to accurately vary these pressures while the engine is running on the test stand. Power Test uses pressure transducers from Setra Systems Inc. (Boxborough, MA).

Setra Systems designs, develops, and manufacturers high accuracy electronic pressure sensors and other electronic measurement instruments used primarily by process and manufacturing industries, federal agencies, and research laboratories. Setra Systems' pressure sensors have a patented capacitive transducer design and proprietary circuitry, which produces a strong signal and an accurate output.

How the sensor works

In a typical configuration, a compact housing contains two closely spaced, parallel, electrically isolated metallic surfaces, one of which is a diaphragm capable of slight flexing under applied pressure. These surfaces are mounted so that a minute change in applied pressure alters the gap between them, creating a variable capacitor. The resulting change in capacitance is detected and converted to a proportional high-level analog signal. Setra's Model 209 Industrial/OEM Pressure Transducer withstands mechanical shock and vibration, thermal shock, corrosion, and other extremes found in the harsh dynamometer testing environment.

'We needed versatility in the pressure ranges that we were sensing,' Mr. Bergst explains. Setra customizes the Model 209 to Power Test's specifications, ranges of 15 psi, 0-2 psi, 0-20 psi, and 5-100 psi, compared to the Model 209's standard range of 0-50 psi or 0-100 psi for low pressure measurement. Setra Systems product manager, Jean Collins, says 'The transducers' capacitive design allows for simple modifications to meet our customers' wide range of needs, such as Power Test's request for uncommon pressure ranges.' Additionally, Mr. Bergst explains, supplying the wide range of pressures in the same package avoided the need to use multiple sensor manufacturers, simplifying design, procurement, and technical assistance.

Because pressure transducers have an amplified output rather than a millivolt output, 'we don't have to amplify the signal output,' explains Mr. Bergst. This means the data collected cannot be distorted due to amplification, resulting in more accurate measurements and a more efficient engine.

In addition to Model 209, Power Test uses Setra's Model 276 Barometric Pressure Transducer. Engine performance is dictated by a variety of conditions, including atmospheric pressure, so engineers must compensate for varying barometric pressures. Engines tuned at sea level likely will have decreased performance at higher elevations. 'Measuring atmospheric pressure is necessary to correct the amount of horsepower generated by the engine,' says Mr. Bergst.

To ensure engine quality, performance, torque, and environmentally correct emissions, engine testers must run the engine under road conditions. Those tests rely on the accuracy of the dynamometer's pressure transducers.

For more information about Setra Systems, visit www.setra.com or go online to www.controleng.com/freeinfo . Information about Power Test Inc. is located on line at www.pwrtst.com .

Comments? E-mail djohnson@reedbusiness.com


Author Information

Richard Pansire is an applications engineer for Setra Systems Inc.




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