Study on nonlinear ignition characteristics and dilution gas effect of n-dodecane methane dual fuel

doi:10.11949/0438-1157.20241216

Abstract

Abstract:

This study systematically investigates the ignition characteristics of n-dodecane-methane dual-fuel mixtures in low-to-intermediate temperature conditions using experimental and numerical simulation methods. The ignition delay times of the dual-fuel mixtures, obtained from rapid compression machine experiments, reveal a nonlinear promoting effect of n-dodecane addition on ignition. Furthermore, the type of diluent gas significantly affects the ignition characteristics of the dual-fuel mixture. Combined with the newly developed reaction kinetic mechanism (Mai2024), the experimental data were numerically simulated and analyzed to reveal the mechanism of action of n-dodecane addition and the type of dilution gas on the dual fuel ignition. The experimental data align well with the model predictions, verifying the accuracy of the Mai2024 model in predicting the ignition characteristics of n-dodecane-methane dual-fuel mixtures. The results indicate that adding n-dodecane promotes ignition in a nonlinear manner, consistent with a nonlinear increase in the ·OH radical production rate. The nonlinear promoting effect of n-dodecane addition on ignition is partly due to its low-temperature oxidation process, which enhances the generation and accumulation of the radical pool, and partly from the heat release of its low-temperature oxidation, which raises the system temperature. Additionally, the type of diluent gas has little impact on the first-stage ignition of the fuel, but for total ignition delay time, differences in the thermal properties of the diluent gas play a decisive role in the low-temperature region, while chemical effects primarily influence ignition characteristics at higher temperatures.

Key words: n-dodecane, methane, dual fuel, ignition delay time, reaction kinetics, rapid compression machine

摘要：

本研究通过实验和数值模拟方法，系统地研究了正十二烷-甲烷双燃料混合物在中低温条件下的着火特性。通过快速压缩机实验中获取的双燃料着火延迟时间结果，发现正十二烷的添加对双燃料混合物的着火有非线性的促进作用。此外，稀释气体的种类也会显著影响双燃料混合物的着火特性。结合最新开发的反应动力学机理（Mai2024），对实验数据进行了数值模拟和机理分析，以揭示正十二烷的添加以及稀释气体的种类对双燃料着火的作用机制。实验数据与机理预测结果具有较好的一致性，验证了Mai2024机理在预测正十二烷-甲烷双燃料混合物着火特性方面的准确性。研究结果表明，添加正十二烷可以促进双燃料混合物着火，这种促进作用是非线性的，且与·OH自由基产率的非线性增长是一致的。正十二烷添加对着火的非线性促进作用一方面是由于其低温氧化过程可以促进自由基池的生成和累积；另一方面是由于其低温氧化过程放热使得系统温度升高。此外，稀释气体的种类对燃料第一阶段着火过程影响较小。但对于总着火延迟时间，稀释气体的热物性差异在低温区域起到了决定性作用；而化学效应主要在更高温区域影响双燃料的着火特性。

关键词: 正十二烷, 甲烷, 燃料, 着火延迟时间, 反应动力学, 快速压缩机

CLC Number:

TQ 511

Zhaoming MAI, Yingtao WU, Wei WANG, Haibao MU, Zuohua HUANG, Chenglong TANG. Study on nonlinear ignition characteristics and dilution gas effect of n-dodecane methane dual fuel[J]. CIESC Journal, 2025, 76(6): 3115-3124.

麦棹铭, 武颖韬, 王维, 穆海宝, 黄佐华, 汤成龙. 正十二烷-甲烷双燃料非线性着火特性及稀释气体效应研究[J]. 化工学报, 2025, 76(6): 3115-3124.

Figures/Tables 11

Fig.1 Schematic diagram of RCM platform

Fig.2 Typical RCM pressure history and IDT definition

Fig.3 The measured and model-predicted IDTs of n-C12H26/CH4 binary mixtures with different n-C12H26 contents at 5 bar and 10 bar

Fig.4 The measured and model-predicted IDTs of n-C12H26/CH4 binary mixtures with 100% and 20% n-C12H26 content under different dilution gas conditions

Fig.5 Evolution of key species and temperature of the n-C12H26/CH4 binary mixture with 2.7% and 20% n-C12H26 content as the normalized times

Fig.6 The evolution of IDTs and maximum ·OH ROP of n-C12H26/CH4 binary mixture with various n-C12H26 content

Fig.7 Normalized ROP for ·OH radicals for n-C12H26/CH4 binary mixture with 2.7% (a) and 20% (b) n-C12H26 content before total ignition

Fig.8 Major endothermic and exothermic reactions for n-C12H26/CH4 binary mixture with 2.7% (a) and 20% (b) n-C12H26 content before total ignition

Fig.9 IDTs of n-C12H26/CH4 binary mixture with 20% n-C12H26 content under 5 bar and different dilution gas conditions

Fig.10 Evolution of key species, temperature, specific heat and accumulated heat release of n-C12H26/CH4 binary mixture with 20% n-C12H26 content and different dilution gas under 5 bar and 680 K conditions

Fig.11 Sensitivity analysis of n-C12H26/CH4 binary mixture with 20% n-C12H26 content diluted with different inert gases at 5 bar, 680 K, and 800 K

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