Search

The development of methanol/diesel dual-fuel engines urgently requires further study on chemical kinetic models for binary fuels. Ignition delay of lean and stoichiometric methanol/n-heptane mixtures (30/70, 50/50, 70/30, and 90/10) diluted with argon was investigated at high temperature (T = 1195 K–1514 K) and low pressure (p = 2 bar) using an aerosol shock tube and a detailed LLNL3.1 mechanism. The results indicated that LLNL3.1 mechanism agreed well with the current measurements. An increase in methanol can accelerate the ignition process at Ф = 1, because of the key radical---HO2, produced by CH2OH + O2=CH2O + HO2, which was affected by the methanol concentration. HO2 would subsequently attack the parent fuels and combine with H radical (HO2+H = 2OH), leading to the booming radical pool. For lean mixtures, n-heptane promoted the reactivity of system due to its high sensitivity to reaction H + O2=O + OH. The higher initial O2 concentration expedited this reaction and shortened the IDT. Besides, both methanol and n-heptane undergo H-abstraction reaction mostly by H radical, however, these reactions showed an inhibition effect on reactivity. This is caused by the competition for H radical between O2 and the parent fuels. Also, the fuel radicals, produced by C7H15-3, had a low decomposition reaction rate thus slowing down the chain branching and suppressing the reactivity of system. • Ignition characteristics of methanol/n-heptane mixtures were studied by shock tube and mechanism. • Methanol accelerated the auto-ignition for stoichiometric mixtures due to the HO2 radical. • N-heptane promoted the reactivity for lean mixtures due to its high O2 sensitivity. • H-abstraction of the parent fuels by H radical showed an inhibition on auto-ignition. [ABSTRACT FROM AUTHOR]

To acquire ignition control methods for dual-fuel marine engine and HCCI engine, ignition characteristics of lean n-heptane/methane mixture under pressure of 2.0 bar and temperature range from 1241 to 1825 K were studied by shock tube and CHEMKIN with LLNL3.1 mechanism. And ignition processes under temperature range from 700 to 1200 K and pressure range from 40 to 140 bar were investigated by CHEMKIN with NUI mechanism. The results illuminate that at low-pressure high-temperature condition, n-heptane's replacement and the increase of n-heptane content obviously reduced ignition delay times (IDT). The reduction degree of IDT decreased when n-heptane content was high. N-heptane's addition also reduced IDT. But this reduction magnitude was less than that of n-heptane's replacement. Methane's addition slightly inhibited n-heptane's auto-ignition. The reaction time of n-heptane was obviously earlier than that of methane. N-heptane decomposition induced radical formation firstly, which triggered subsequent n-heptane's H-abstraction and the advance of methane's oxidation. At ultra-high-pressure low-temperature condition, increasing n-heptane's content enhanced negative temperature coefficient (NTC) behavior. The end time point of complete consumption of two fuels was the same. Low-temperature condition inhibited n-heptane decomposition, with n-heptane's H-abstraction dominating ignition process. • Ignition properties of CH4/n-C7H16 mixture was revealed by shock tube and mechanisms. • Active radicals formed from n-heptane's decomposition advanced methane's oxidation. • Methane's addition slightly retarded the ignition of pure n-heptane mixture. • The results provided ignition control method for natural-gas/diesel dual-fuel engine. [ABSTRACT FROM AUTHOR]