Machine Design

Oil lasts longer in diesels, thanks to novel viscosity sensor

Embedded viscometers using acoustic-wave-sensing technology give early warnings of oil degradation and contamination in diesel engines that could lead to premature engine failure.

The acoustic-wave sensor and its associated circuitry reside in a 25-mm-long, 14-mm-diameter threaded stud that bolts into the engine. The viscosity of the oil is measured as it flows across the head of the sensor.

The detector spots changes in fluid viscosity as the engine runs, alerting operators before there is serious damage. Viscosity, the measure of a fluid's resistance to flow, is a key physical parameter in lubricants that affect product performance and equipment life. Yet viscosity has been difficult to measure out-side the lab. Conventional mechanical and electromechanical viscometers are difficult to adapt to online measurements. Their size and complexity limit their use in embedded applications where temperature, shear rate, and other variables differ from those found in labs.

A new solid-state sensor made by Biode Inc., Westbrook, Maine, uses acoustic surface waves to measure oil viscosity. The 0.5-in.-diameter sensor conforms to half-inch NPT and M14 thread standards. The device bolts into the engine at a point where it touches the oil flow. The oscillator circuitry, analog instrumentation, processor, CANbus drivers, and voltage regulators reside within the sensor body.

The viscometer combines solid-state surface chemistry with ultra-sensitive acoustics to create a sensor immune to shock and capable of withstanding 30-g vibrations. The sensor is unaffected by static, laminar, or turbulent flows so it can measure viscosity in-line in high-flow applications. Measurements span 0 to beyond 10,000 cP with ±3% repeatability at temperatures from 20 to 135°C.

The onboard electronics, temperature, and communication capabilities support Profibus, CAN-bus, and DeviceNet, as well as other communication protocols. The sensor design embeds calibration and adaptive baseline data, instrumentation, and processing power in a small device that operates reliably over the wide temperature range found under the hood of vehicles.

As long as oil was relatively inexpensive, most truck operators followed conservative preventive maintenance schedules. Lubricants were replaced well before the end of their service life. Not only is the price of oil higher today, but mechanics must dispose of the old oil in an approved manner. When one truck takes 14 quarts, oil changes can run into hundreds of dollars. By monitoring the condition of the oil, maintenance personnel can reduce change intervals to an as-needed basis.

A second sensor is planned to monitor diesel-fuel viscosity at the injectors. The sensor data should help reduce pollutants to meet new engine emission requirements for EPA 2010 heavy and light-duty emission regulations. Similar regulations are planned for the EU. Composition of the fuel at the injector is dynamically controlled to generate lower emissions and maintain engine-operating parameters for fuel economy and long life cycles.

Biode Inc., (207) 856-6977,

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