Photoelectric Detection And Numerical Study On The Ignition Delay Of Dimethyl Ether

Dimethyl Ether (DME) is a promising clean alternative fuel for diesel engines. In the present thesis both experimental investigations and numerical calculations are employed to study the ignition process of DME in a direct injection engine, and the variation tendency of ignition delay period of DME with engine working conditions is also discussed.Based on broad references reading, the characteristics of DME as a clean fuel for internal combustion engines and its applications are generally concluded. A numerical method of the ignition process of DME and applications of the optic-fiber combustion sensor in studying combustion processes of internal combustion engines are reviewed. Based on the requirements of only a single optical sensing path, a light transmitted by the fibre and a photodetector,a novel intrinsic optical fibre sensor for detection of DME ignition has been designed, built and tested. This sensor is intended for use in measuring ignition delay period of ZS195 DI diesel engine fuelled with DME. A preliminary investigation has been undertaken to use the optical fibre sensor for ignition delay measurement. The sensor values of DME ignition are compared with the results obtained by experiments. It has been shown that this fibre optic combustion sensor is of simple construction and operation and is particularly useful for in-cylinder combustion visualization and parameter measurements.The self-made optic-fiber combustion sensor is used for the photoelectric detections of the ignition process of DME in the ZS195 DI engine. And the ignition delay time can be obtained by combining the optoelectronic signal processing with fuel tube pressure waves obtained by a piezoelectric sensor. The results show that under idle conditions good agreements are obtained by comparing with similar research results; while under different load conditions, the results have a little discrepancy with the theoretical values, but the trend matches well with theoretical analysis.A new calculation method of the ignition delay period of DME in DI engines is developed, which includes physical and chemical ignition delay period. They are calculated by using a gas jet program and CHEMKIN4.0 commercial software separately, and the result is the sum of these two. Under idle condition, the calculation results have good agreements with the experimental results when the engine speed is high, but there are still some discrepancies for the low speed cases. Under load-running condition, the results match well with the experimental data. Comparisons between numerical and experimental results prove that the calculation method of the ignition delay period for DME combustion in this thesis has a good feasibility and is also appropriate for engineering applications.