稀释气体对二甲醚着火延迟特性的影响

在上止点压力1.5 MPa,上止点温度670~795 K,当量比为1的实验条件下,利用快速压缩机(RCM)研究了N_2、N_2/Ar(50%/50%)和Ar/CO_2(61.2%/38.8%)稀释气体对二甲醚(DME)着火延迟期的影响。利用CHMKINPRO软件在较大温度范围内进行了模拟研究。结果表明:不同稀释气体组分对二甲醚混合气体第一阶段着火延迟期影响很小,但对总着火延迟期具有较大的影响,尤其在负温度系数(NTC)区间的起点温度附近。与N_2相比,N_2/Ar(50%/50%)使得实验中总着火延迟期缩短30%。稀释气体的化学效应对第一阶段着火延迟期和总着火延迟期的影响均很小。在低温区间和NTC区间,稀释气体的热效应起主导作用,而当上止点温度超过NTC区间时,CO_2的化学效应影响增强且超过热效应而起到主导作用。随稀释率增加,DME混合气体第一阶段着火延迟期略有延长,而总着火延迟期出现明显延长,且总着火延迟期的NTC现象变得更加明显。

Effects of Diluent Gases on Ignition Delays Characteristics of Dimethyl Ether

Effects of diluent gases composition on ignition delays of dimethyl ether (DME) were investigated at compressed pressure of 1.5MPa, compressed temperature from 670K to 795K and equivalence ratio of 1 by using a rapid compression machine (RCM). The diluent gases considered were nitrogen (N2), mixture of N2 and argon (Ar) at mole ratio of 50% to 50% and mixture of Ar and carbon dioxide (CO2) at mole ratio of 61.2% to 38.8%. The simulation study was performed over a wider temperature range based on CHMKIN-PRO software. The results showed that diluent gases composition had little impact on the first-stage ignition delay. However, significant differences in the total ignition delay were observed, especially in the negative temperature coefficient (NTC) region. Compared with N2, mixture of N2 and Ar decreased the total ignition delay by 30%. The chemical effect of diluent gases composition on the first-stage and total ignition delays was negligible. The thermal effect was dominant factor in the low temperature and NTC regions, however, the chemical effect of CO2 enhanced and exceeded the thermal effect in the temperature region beyond the NTC region. With the increase of N2 dilution ratio, the first-stage ignition delay was slightly increased, while a significant increase in the total ignition delay was observed. Moreover, the NTC behavior of total ignition delay was noted to become more pronounced at high N2 dilution ratio.