Development And Experimental Research Of A Rapid Compression Machine

In order to study the combustion characteristics such as ignition delay time of IC engine alternative fuel, based on a review of structure and feature of rapid compression(expansion) machines in china and abroad, a rapid compression machine test bench is designed and developed. The design thought and structure of pneumatic driving system, hydraulic control system, combustion and acquisition system, gas supply system and heating system are introduced. The average compression speed of the rapid compression machine is 10m/s approximately, compression time is 20-25 ms, half-pressure compression time is 2.4ms. Compression ratio can be adjusted in the range of 8-17 and the maximum compressed temperature is 1800 K approximately.The compression and auto-ignition performance tests of the developed rapid compression machine test bench are carried out. The compression performance of rapid compression machine is optimized by adjusting the T-shaped channel structure on hydraulic piston and two-stage buffer on the connecting rod at the front of the piston. Multiple repeated experiments indicate that data collection and repeatability of combustion experiments based on the rapid compression machine are both good. Experimental research on the influences of factors such as driving pressure, compression ratio, initial pressure and N2 dilution ratio on the two-stage ignition delay time of DME-O2-N2 mixture is conducted. The results show that with the increasing driving pressure, both the first stage and total ignition delay time of DME-O2-N2 mixture tend to be extended. Under different initial pressures, the total ignition delay time of the DME-O2-N2 mixture presents variable trends with the increasing compression ratio and nitrogen dilution ratio.Based on the developed rapid compression machine, a study on the influence of equivalent ratio and hydrogen blending on the ignition delay time of DME-O2-N2 mixture, as well as the preliminary investigation on the influence factors of ignition delay time of CH4-O2-Ar mixture are carried out. Experimental results and modeling results based on corresponding combustion mechanism are compared and analyzed. The results of experiment and modeling analysis show that with the increasing hydrogen blending ratio, there is only little change about the first stage ignition delay time of DME-O2-N2 mixture. Hydrogen blending reduces the initial concentration of DME and the heat release rate in the low temperature stage. Meanwhile, the increase of H2 will hinder the decomposition of CH3OCH3 during the overall reaction of the DME-O2-N2 mixture and delays the decomposition of CH2 O after the low temperature reaction stage, making the ignition delay time of the mixture extend in the second stage. With the increasing equivalence ratio and compressed pressure, the first stage ignition delay time of the DME-O2-N2 mixture only has little change and the second stage ignition delay time extends gradually. The reason for the increasing equivalence ratio can shorten the total ignition delay time of the DME-O2-N2 mixture lies in that, in the case of the dilution rate unchanged, the declining initial concentration of O2 and the rising initial concentration of DME get the heat release rate in the low temperature reaction stage increased, therefore, the reaction is accelerated. The ignition delay time of CH4-O2-Ar mixture fluctuates within a certain range with the change of the driving pressure. When the driving pressure is relatively low, the ignition delay time of mixture is significantly extended; with the increasing initial pressure, the ignition delay time of CH4-O2-Ar mixture tends to be shortened; while the ignition delay time of CH4-O2-Ar mixture tends to be extended with the increasing equivalence ratio.