Optical Piston Temperature Measurement in an Internal Combustion Engine 2011-01-0407
In the last ten year the mechanical power output of car engine
increased significantly. This result has been possible especially
through new injection systems that brought to an optimization of
the combustion (direct injection, common rail) and to an
improvement of the turbocharging. Moreover, these technical devices
brought a reduction of the exhaust emissions and an increasing of
the engine efficiency. In particular, the specific power is
increased from 34 kW/liter of 1992 to the 63 kW/liter of 2010.
Furthermore, the pressure peaks into the combustion chamber and the
fuel injection pressure have been increased to the aim of emission
reduction and higher engine efficiency.
In this scenario, car manufacturers are following the direction
of the engine downsizing that means to have the same engine power
by a lower engine displacement. The downsizing has as main
consequence thermal risks especially for the hot parts of the
combustion chamber (exhaust valves, spark plug body and piston)
because these parts have an increased high heat load and thermal
stress. These temperatures could have as main consequence to the
risk for engine damage by irregular combustion due to "surface
ignition" by hot spot or by deposit of the combustion
In this paper a method for optical measurement of piston
temperature during the fired and unfired operation of an internal
combustion engine has been developed.
An optical access to the combustion chamber is achieved by an
optical element made from sapphire lens that can be located in a
special spark plug or other engine parts (injectors, cylinder
head). The thermal radiation of the piston observed with this
optical element is guided to the detector with optical fibers. As a
detector InGaAs-photodiodes are used, which allow a detection of
the infrared radiation up to 2.6 μm.
The relation between the signal intensity and piston temperature
was determined outside the engine in a calibration unit: the piston
was heated up to 400°C. In the calibration unit the sensor and the
piston are arranged in the same geometry as in the combustion
chamber. During cool down, the thermal radiation is simultaneously
measured with the temperature of the piston surface, obtained from
AVL uses optical sensors in spark plugs to investigate
combustion phenomena in spark-ignited internal combustion engines.
In a recent application the measurement of valve temperatures has
been demonstrated using these sensors.
In this paper the possibility to measure piston temperatures
with this measurement system is investigated. For this purpose
following tasks have been performed: - The measurement range was
extended from 400° down to 200° by selecting appropriate optical
materials and detectors. - A calibration unit was developed to
determine the relation between radiation signal and piston
temperature. - The piston temperature was measured for different
pistons in a single-cylinder research engine.