Portable Measurement of Fuel Dilution in Used Engine Oil

Contamination of fuel in used engine oil is an important issue and demands considerable attention from reliability engineers. To combat this problem, engine oil samples are regularly checked on site, or monitored by a remote lab checking fuel dilution levels.

This article describes the working of the Fuel Sniffer and how its method of operation compares to Flash Point and Gas Chromatography Mass Spectrometry (GC-MS) methods.

A number of methods are available to monitor fuel contamination indirectly, such as using costly instrumentation like FTIR or GC-MS, using change of flash point or viscosity as an indication, and complex data analysis algorithms.

There is a definite need for a direct, simple, and inexpensive measurement tool which can check the contamination of fuel in the field directly, to allow reliability engineers to make quick decisions on site. The SpectroFDM Q600 is one such instrument that addresses the market needs to provide quick and simple measurement of fuel dilution in engine oils.

Chemical Microsensors

The US Navy and Microsensor Systems teamed up to develop a compact, rugged and reliable instrument based on the SAW microsensor. Following a detailed assessment and testing period, the US Navy bought more than 100 fuel dilution meters for use on ships. This instrument was the previous version of the present Fuel Sniffer which applies the same technology.

Fuel sniffer is now being extensively used by laboratory technicians and maintenance professionals across the globe supporting marine, railway, automotive and heavy equipment fleets in operation for engine maintenance.

Operation of Fuel Sniffer

SAW Sensor Signal Response Diagram

Figure 1. SAW Sensor Signal Response Diagram

A Surface Acoustic Wave (SAW) Vapor Microsensor is used by the Fuel Sniffer to measure fuel concentration in used lubricating oil samples, by sampling the headspace in the sample bottle.

Based on Henry's Law, the instrument presumes that the concentration of fuel vapor is directly related to the fuel within in the oil sample. This variation in frequency is the basis of the Fuel Sniffer's detection.

Flash Point and GC-MS Technologies

Before the introduction of the Fuel Sniffer, Flash Point and GC-MS technologies were predominantly used by customers to detect dilution of fuel. GC-MS is a technique that integrates the features of mass spectrometry and gas-liquid chromatography to detect different substances present in a test sample. This method is known as the "gold standard" for forensic substance identification, as it is employed to carry out a particular test. Although this test detects the presence of a specific substance in a given sample, it is rather expensive and in order to obtain good results a highly skilled chemist is required to operate the GC-MS instrument.

Flash Point tests can prove comparatively fast and precise; however, it is not as fast or as easy as the Fuel Sniffer. In contrast, the SpectroFDM Q600 Fuel Sniffer offers an innovative and cost-effective solution for measuring contamination of fuel in used engine oil. It does not require any consumables or chemicals, thus making it easy and economical to use. In addition, measurements can be performed instantly and accurately. The instrument provides repeatable and precise measurements and with its compact size and simple user interface it is suitable for both field and laboratory applications.

Furthermore, the Fuel Sniffer provides a high level of safety compared to Flash Point methods, since it reduces exposure to inhalation and fire hazards from heating fuel samples. It also eliminates the need for correlation tables to acquire the known percentage of fuel.

FTIR testing of fuel depends mainly on careful baselining of the blank oil matrix and individual fuel calibrations. In the spectra regions, the absorbance peak utilized to identify fuel is not very sensitive, and careful calibration has to be performed by trained professionals. Moreover, different fuels will contain different absorbance bands that could be missed by the calibration peak. These matrix and calibration issues do not affect the Fuel Sniffer.

General Operation of Fuel Sniffer

Filling Sample Bottles

Figure 2. Filling Sample Bottles

Labeled Sample Bottles

Figure 3. Labeled Sample Bottles

Clamp and Sample Bottle Platform

Figure 4. Clamp and Sample Bottle Platform

Before the actual measurement, the Fuel Sniffer must be calibrated with a typical concentration containing 5% fuel in a lubricant base, akin to the samples to be examined. The instrument’s response to the dilution of fuel is linear and makes no provisions to utilize any other value of calibration standard. In case another level of dilution is utilized below or above this standard, the instrument will under or over estimate the actual reading respectively.


The SpectroFDM Q600 offers a portable and economical solution for detecting fuel dilution in used oil samples. In contrast to GC-MS, it is less costly to use for single point calibrations and offers precise and repeatable results. Moreover, the instrument does not need any consumables or chemicals and proves ideal for onsite engine maintenance.

This information has been sourced, reviewed and adapted from materials provided by AMETEK Spectro Scientific.

For more information on this source, please visit AMETEK Spectro Scientific.


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