Advanced science.  Applied technology.


Design of an Optical Periscope System and Phosphor Thermometry of Thermal Coatings on the Piston of a Compression Ignition Engine, 03-R6048

Principal Investigator
Inclusive Dates 
04/01/20 to 10/01/21


Thermal insulative coatings are an area of high interest in the diesel engine community: These coatings offer the potential to reduce heat losses through the piston to the engine oil and coolant. The energy can then serve to increase engine power output and to increase exhaust temperatures, which is useful for aftertreatment thermal management and waste heat recovery. However, the design and development of these coatings is experimentally challenging as it is impossible to directly measure temperatures of the piston surface with these coatings.

To address this gap, the objective of this project is designing and installing an optical periscope into the cylinder head of a single-cylinder diesel engine and applying a non-contact phosphor thermometry method to directly measure the surface temperature of the piston, both with and without, the insulative coating. These measurements will serve to validate CFD and FEA models of the coating and quantify the performance of the coatings in situ.


An optical periscope has been designed to replace one of the exhaust valves on the engine. This periscope will use a window to seal the combustion chamber and a metal sleeve to seal the water passages in the cylinder head. A mirror arrangement at the top of the sleeve will allow laser light to be introduced to the phosphor and a camera or spectrometer to be used to record the phosphorescent signal, which is correlated to the temperature of the phosphor. Decay times for typical phosphors will allow for the measurement of temperature at 2°CA intervals during the engine cycle.

Pie chart showing the energy flow distribution in a diesel engine.

Figure 1: Energy flow distribution in a diesel engine.

Example of optical periscope arrangement.

Figure 2: Example of optical periscope arrangement.


The modified engine components and optical periscope are complete and measurements are scheduled for early Summer 2021.