Mechanism of Methane Addition Affects the Ignition Process of n-heptane under Dual Fuel Engine-Like Conditions
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https://doi.org/10.1007/s11630-020-1260-z
Article ID: 1003-2169(2020)00-0000-00
Mechanism of Methane Addition Affects the Ignition Process of n-heptane under Dual Fuel Engine-Like Conditions LIU Zongkuan, ZHOU Lei*, ZHAO Wanhui, QI Jiayue, WEI Haiqiao* State Key Laboratory of Engines, Tianjin University, Tianjin 300072, China © Science Press, Institute of Engineering Thermophysics, CAS and Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract: For saving energy and protecting the environment, natural gas has been widely used in internal combustion engines, which makes the study on the ignition characteristics of natural gas/diesel mixtures important. In this work, the effects of trace methane addition on the ignition delay of n-heptane/air mixtures are numerically studied using a detailed n-heptane mechanism under marine engine-like conditions. The simulations are carried out based on the software CHEMKIN-PRO 18.0 with a closed homogeneous reactor. Results show that the prolonged ignition delay times (IDs) of n-heptane/air mixtures are observed over the whole initial temperature range after methane is added, and the increment of IDs in the negative temperature coefficient (NTC) region is significantly higher than that in high temperature region. The sensitivity analysis indicates that both inhibition and promotion effects of important elementary reactions on n-heptane oxidation are weakened because of methane addition. However, the weakening influence on the promoting effect is more prominent. In addition, the inhibition effect of some elementary reactions that are related to the methane oxidation is enhanced. Thus, the IDs of n-heptane/air mixture are prolonged. The analyses of reaction rate of production (ROP) show that the both the production and consumption rates of key radicals decrease significantly in NTC region after methane is added, but it is negligible in the high temperature region. The study can extend the theoretical basis of ignition characteristics of methane/n-heptane blends under elevated temperatures and pressures.
Keywords: ignition, methane addition, n-heptane, low-temperature reaction pathways
1. Introduction With the depletion of petroleum resources, energy conservation has raised significant public concern. And it is widely accepted that the emissions of internal combustion engine (ICE) are remarkedly increased with the growing number of vehicles [1‒5]. For saving energy and protecting the environment, some relevant agencies, such as IMO (International Maritime Organization) and US EPA (U.S. Environmental Protection Agency), promulgated the newest emission regulations, leading to Received: Apr 01, 2019 AE: CHEN Zheng
a worldwide interest in developing the environmentally alternative energy. Natural gas has attracted much attention for its potentials such as clean-burning qualities, the highest H to C ratio, and widespread distribution infrastructure [6, 7]. In this regard, the application of natural gas in ICE is a considerable way to meet emission regulations [8]. Natural
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