Optical Methods for the Measurement of the Temperature and Concentration Distribution in Combustion Chambers

Two kinds of optical methods for the measurement of the temperature and concentration distribution in combustion chambers by means of the real-time laser holographic interferometry are presented in this paper, which are respectively the one-wavelength laser holographic interferometric technique and the two-wavelength laser holographic interferometric technique. The basic measurement principles of these laser holographic interferometric techniques, the characteristic features of their optical arrangements, the experimental device and testing procedure, and the formula of evaluation of holographic interferograms are described in detail.

The experimental results show that the one-wavelength laser holographic interferometric technique is suited to research the temperature distribution and its variation processes in the combustion chambers in detail after combined with a high speed camera, and the two-wavelength laser holographic interferometric technique is suited to investigate the coupled temperature and concentration distribution in the combustion chambers during the period of the fuel evaporation.

MUCH RESEARCH WORK has focusd on the investigation of the temperature and concentration distribution in the fuel evaporation process in order to ascertain the formation process of the mixture of air fuel-vapor in the combustion chambers in diesel engines and to obtain the good performance of diesel engines [1]*. Many methods have been used for many years in measuring the temperature and concentration distribution [2]. For example, the most common method is that the temperature distribution in a combustion chamber of a diesel engine is measured by using the thermocouples. However the measurement results from thermocouples are unsatisfactoried because of the poor response property, the effects on the flow field in the combustion chamber, and the point by point measurement information. Some optical methods, such as Schlieren and Shadowgraph methods, can not be used for the quantitative measurements although they can be used for the observation of the in-cylinder process and can obtain the information about a whole field by the evaluation of photographs. In Mach-Zehnder interferometry, the imperfections of windows, lenses and mirrors will influence the accuracy of measurement, and the adjustment of equipment is difficult.

Since the laser is invented, the laser holographic interferometic techniques have quickly been developed and have found wide applications. In contrast to conventional interferometric methods, the laser holographic interferometric techniqes offer the considerable advantages of greater experimental and technical simplisity, which means that the necessary optical arrangements are much cheaper; the time needed for adjusting equipment and taking measurements is also greatly reduced; high quality windows, lenses and mirrors are not necessary. In addition, the measurements can be made even in high pressure and high temperature as well as very fast variation process.

In this paper two kinds of optical methods for measurement of temperature and concentration distribution in the combustion chambers are presented, which are respectively the one-wavelength laser holographic interferometric technique and the two-wavelength laser holographic interferometric technique. The basic measurement principles of these laser holographic interferometric techniques, the characteristic features of their optical arrangements, the experimental device and testing procedure, and the formula of evaluation of the holographic interferograms are described in detail. The research work done in this paper provides, the author hope, a solid foundation for the investigation of the temperature and concentration distribution in the fuel evaporation process and for further investigation of the formation process of the air fuel-vapor in the combustion chambers in diesel engines.