Paper 7: Accuracy of and Representative Results Obtained with an Infra-Red Pyrometer Measuring Compression Temperatures

Abstract

In a spark-ignited internal combustion engine there are two zones of interest ( a) the burnt mixture and ( b) the unburnt mixture. Of interest to the authors and to many of their colleagues are the pre-reactions which occur in the unburnt zone. To follow the extent of these pre-reactions both the pressure and the temperature of the unburnt mixture are required. Pressure transducers can be obtained from many commercial establishments, but a temperature pyrometer that can follow the temperature of the unburnt mixture is not commercially available. The current technique uses the absorption, emission characteristic of the water vapour in the cylinder. The use of water vapour as the sensing element is desirable since water vapour is normally in the air which the internal combustion (i.c.) engine breathes. Radiation of a known intensity (known black-body temperature) is passed through the engine, through a band pass filter (H2O water vapour band at 2.6 μ) to an infra-red detector. The output from the detector, after amplification, is fed to a cathode-ray oscilloscope. By suitable means, it is possible to compare the undisturbed radiation from the black body with the black-body radiation after it has experienced absorption emission events during the compression process. The reversal point can be visually observed on the oscillogram. At this reversal point the temperature of the gas and the black body are equal and the crank angle at which this occurs can be determined. Other temperatures and crank angles at which reversal occurs can be observed to obtain the unburnt mixture temperature versus crank angle curve. The authors' experiences with different infra-red detectors and other temperature-measuring techniques, as well as comparison between the velocity of sound method and the infra-red technique, are discussed. Data obtained with the instrument are presented.