IR Speeds Automotive System Testing

by Maurice Lee MIIE(mech),
A motor industry Test Engineer with 30+ years experience
In the automotive testing world, thermal imaging cameras are a extremely useful tools. Here are a few examples of how I have used thermal imaging cameras to save time and money within the automotive field.
Reduce Defroster Testing Time with Thermal Imaging!
The design of windshield defrost demist ducting is complex and hampered by the dimensional constraints due to other essential vehicle parts. It can be difficult to provide an adequate and evenly distributed airflow to the inner face of the glass.
To validate a design, a typical defrost development test is as follows:-
Following design guidelines for the intended market a vehicle needs to be chilled to -20°C or so and soaked (to achieve uniform temperature) for up to 8 hours to ensure a known start point. The windshield has a known amount of water sprayed on and is left to cure for several minutes to establish uniform crystal consistency. The vehicle engine is started and allowed to idle with the appropriate heater/windshield defrost settings.  Here is where a thermal imaging camera is needed.
As the engine heats up and warm air flows through the defrost ducting, a thermal imaging photo shows the thaw pattern developing on the screen.
At set intervals, a recording is made of this thaw pattern.  In addition, a certain area of glass must be clear of ice within a predefined time, as defined by the Testing Standard used.

Thermal imaging photo of uneven screen heat distribution.

Thermal imaging photo of even distribution, but note undesirable cold region.

Processing these results with a thermal imaging camera takes some time.  If the photos from the thermal imaging camera show that the defrost system provides uneven or inadequate thawing and needs improvement, the whole costly process needs to be repeated until we get it right.
If a thermal imaging camera is used to look at the outside of the glass under the same test conditions, but with the vehicle stabilized at normal lab ambient (say 20°C); a pattern appears on the glass within a couple of minutes. This pattern, once formed, does not seem to significantly vary in shape, only in intensity.
Design alterations can be made to the duct and outlet apertures and minutes later the thermal imaging inspection can be repeated. Once the desired pattern is achieved, the expensive ‘cold’ test can be attempted.
Of course this method does not initially guarantee success, as time has not been a factor in the process but uniform or desired temperature distribution can quickly be resolved.
The thaw process starts due to a certain glass surface temperature. If thermal imaging cameras are used to record a low ambient defrost test; time, glass temperature, and thaw pattern data can be collected.
If the same vehicle is then allowed to achieve normal ambient throughout (e.g. +20°C) and a ‘warm’ repeat of the defrost test is carried out, there will be a correlation between the glass temperatures in relation to time.  It should therefore then be possible to carry out defrost development tests with reasonable confidence at ambient conditions.
See the "air" with Thermal Imaging!
Automotive Heating Ventilation & Cooling (HVAC) engineer use thermal imaging technology to establish and maintain comfortable ambient conditions within vehicles.
In order to run thermal imaging tests, new or modified systems, the passenger compartment air circulation needs to be measured in some way. Air movement around a vehicle is quite slow, the fastest within the passenger compartment being at the outlet of cooling/heating vents.
These outlets are quite small in size, and when measuring equipment is placed in the airflow it can both disturb and restrict, thus affecting the measurements being taken.
As with windshield defrost ducting, climate control ducting is a complex shape made to follow a tortuous route. The airflow from most ducts is often very difficult to direct into a laminar uniform pattern. Any information about the actual pressure/flow profile from a duct can assist in design improvements.
There is a product available which is a paper composite material formed in a sheet of honeycomb perforations.  Using an 8mm thickness with a honeycomb size of 4mm with a paper wall thickness to the cells, placed at 90 degrees to the airflow it presents very small disturbance or restriction.

Sample of the honeycomb sheet used to visualize airflow

Thermal imaging photo of the honeycomb in hot airflow from left face vent.

Thermal imaging photo of the honeycomb sheet positioned at occupant head level, across a vehicle with the central vent set to hot/max airflow.

Being made of paper, it conducts heat poorly while due to its depth (contact area) and small mass readily assumes the temperature of the air passing through the honeycomb.  If a thermal imaging camera is directed at the honeycomb, but in the airflow, the thermal imaging camera bulk will restrict the airflow and the thermal imaging photo will be of the thin edges of the mesh.
If the thermal imaging camera is angled at the honeycomb sufficient to ‘blank off’ sight of the airflow source, the thermal imaging photo will be of the inner walls of the honeycomb, which is radiating the IR waves allowing the thermal imaging camera to measure the temperature of the air flowing across it.
Uneven air distribution from a vent will readily display a temperature profile across the target area. This alone can be used to develop duct and outlet design.
Maurice receives an InfraMation Executive Attaché Case for his newsletter contribution. Published articles also earn credit towards IR recertification

For more information on thermal imaging cameras, please visit http://www.flirthermography.com/cameras/all_cameras.asp

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