二甲醚与氢气稀混合气在中低温条件下的着火延迟特性

Ignition Delay Characteristics of DME/H_2 Lean Mixtures at Low-to-medium Temperature

为了研究二甲醚与氢气稀混合气在中低温条件下的着火延迟特性,利用快速压缩机实验台架测量了二甲醚与氢气稀混合气在上止点温度628~858 K,上止点压力12~22 bar,当量比0.30~1.00,掺氢比0%~85%条件下的着火延迟期。同时,采用有限元分析软件Chemkin-Pro对着火过程进行了模拟计算。实验和模拟研究结果表明:氢气的添加使得着火延迟期呈非线性增加,且在掺氢比超过60%和较低的上止点压力下氢气对着火的抑制效果更加明显;二甲醚与氢气稀混合气在较低当量比0.30下的燃烧与放热出现低温、高温第1阶段和高温第2阶段3个阶段,且随着掺氢比的增加,三阶段的燃烧与放热现象弱化。化学动力学分析表明:二甲醚主要在低温、高温第1阶段反应过程中消耗,氢气主要在高温第2阶段反应中消耗。

To investigate the ignition delay characteristics of DME/H2 mixtures at low-to-medium temperature,ignition delay times of lean DME/H2 mixtures（ hydrogen mole fraction in the fuel mixtures of 0%,50%,60%,70%,and 85%） were measured using a rapid compression machine in the compressed temperature range of 628-858 K at compression pressures of 12-22 bars,the equivalence ratios of0. 30-1. 00,and the hydrogen blend ratio of 0%-85%. A kinetics model is built to simulate the ignition process using finite element software Chemkin-Pro. The results show that the addition of H2 to DME mixtures leads to a nonlinear increase in ignition delay time. The inhibition effect of H2 addition is found to be more pronounced at lower compression pressure with H2 mole fraction of more than 60%. It is alsoobserved that lean DME/H2 mixtures show three stage heat release behaviors at lower equivalence ratio of0. 30,i. e.,the first stage of low temperature heat release（ LTHR） and the second stage of high temperature heat release（ HTHR）,and the third stage of high temperature heat release. Meanwhile,the threestage heat release behavior becomes weak as the H2 mole fraction increases. Further chemical kinetic analysis indicates that DME is mainly consumed during LTHR and the first stage of HTHR whereas H2 is mainly consumed during the second stage of HTHR.