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Have you ever pulled a sample from your machine and taken a step back because of the distinct, pungent road-kill smell permeating from the bottle? What did you do?
Go about business as usual and never think twice about it, or did you recognize that the oil might be contaminated with bacteria and draw another sample for further testing?
Odor, like color, clarity, presence of foam and other characteristics of the oil that can be evaluated with the human senses, can effectively identify degradation or contamination of lubricating oils.
As simple as it seems, smelling your oils should be a regular part of your routine machine inspection process. A lot of caution should be exercised when smelling oil samples. Do not place the bottle directly under your nose - remember, there may be toxic chemicals in the sample.
Rather, wave your hand above the opening to waft the scent toward your face. Sometimes it helps to heat the oil, which increases the likelihood of detecting certain contaminants and degradation by-products.
Scientists are forging ahead with “artificial nose” research to create sensors that can detect thousands of odors for various environmental, medical, food service and industrial applications. Some artificial noses are quarter-sized chip-sensors that convert odors into images on a computer screen.
These chips use fiber optics to create a “picture” based on an assigned signature to the vapors of gases and odors. On the computer screen, the feedback from these sensors appears as a collection of circles, each one representing the fluorescence of the individual odors. It is reported that these sensors can presently detect dozens of individual odors.
A related technology already available for oil analysis is the Fuel Sniffer from Spectro Incorporated, which is used to detect fuel dilution in engines. Originally developed by the U.S. Navy, the technique employs a Surface Acoustic Wave (SAW) vapor microsensor.
When fuel is present in the sample, hydrocarbon vapors are emitted in greater concentration. The Fuel Sniffer employs a sensor material to which the vapors adsorb. The presence of these molecules on the sensor changes the SAW frequency, which is measurable and comparable to a calibration curve to determine the percent fuel.
Odor comparators can help to improve the effectiveness of the human nose. These are special samples known to contain certain contaminants or oil degradation products.
Each bottle is marked to identify its reference material and stored for later reference. When used oil is suspected to have a certain problem, its scent is compared to the reference standard to see if there is a match.
Who “nose,” maybe in the future we will train dogs to sniff out contaminated or degraded lubricants, since they have at least 20 times as many smell receptor cells as humans.
Perhaps we can train them to bark once for bacteria, twice for oxidation and two long barks followed by one short one to signal additive depletion!
Typical Odors From:
Oxidation - sour or pungent odor, acrid (rotten egg) smell or something similar to stale cheese
Thermal Failure - smell of burnt food
Bacteria - stench, road-kill smell
Running High Temperatures - no odor
Contaminants - solvents, refrigerants, degreasers, hydrogen sulfide, gasoline, diesel, kerosene and process chemicals
Amino Acids - fish odor
Nitro Compounds - almond-like scent
Esters (Synthetic Lubricants) and Ketones - perfume odor