The core mechanism is the cornerstone of combustion reaction kinetic models and has a crucial impact on the prediction accuracy of large hydrocarbon combustion mechanisms. At present, there remains no systematic method to compare the effect of different core mechanisms on the combustion mechanisms of large hydrocarbons. In this work, the effects of popular core mechanisms such as AramcoMech1.3, USC Mech II, AramcoMech3.0, and Foundational Fuel Chemistry Model (FFCM-1) on the combustion mechanisms of a large hydrocarbon were compared. Based on these core mechanisms, the lowtemperature combustion mechanisms of the large hydrocarbon (taking n-heptane as an example) have been developed. Meanwhile, the detailed numerical simulation and analysis of these mechanisms have been carried out. Concretely, using automatic generation software ReaxGen, coupled with AramcoMech1.3, USC Mech II, AramcoMech3.0, and FFCM-1, the detailed mechanisms named Mechanism-1(AramcoMech1.3), Mechanism-2(USC Mech II), Mechanism-3(AramcoMech3.0), and Mechanism-4(FFCM-1) for low-temperature combustion of n-heptane have been developed. Among them, the Mechanism-2(USC Mech II) can be referred to our previous work (http://www.cnki.com.cn/Article/CJFDTotal-GCRB201411041.htm). These mechanisms were validated by the ignition delay time and concentration profiles of important species. Numerically predicted results show that Mechanism-1(AramcoMech1.3) is in better agreement with available experimental data than those of other mechanisms. Finally, the sensitivity analysis of these mechanisms was carried out to find the key reactions to ignition sensitivity under low-temperature combustion conditions, and to better understand the models' predicted performance, the differences in reaction pathway analysis of n-heptane were discussed.

The non‐probabilistic reliability theory is a promising methodology for implementing structural reliability analysis in case of scarce statistical data. One of the main obstacles to implement non‐probabilistic reliability analysis is the implication of the limit state function (LSF) for complex structures. This paper aims to establish a surrogate model of the LSF with higher simulation precision, and whereby proposes a response surface method based on the combination of uniform design (UD) and weighted least squares (WLS). At first, the UD method is selected as the sampling method of interval variables to realize the uniform space‐filling of the initial samples, and the sample set is updated by gradually adding the approximate optimal points to increase the sampling density of critical domain. Then, the WLS method is applied to improve the precision of the response surface by adjusting the importance of samples to the function fitting. Finally, a method of constructing sample weights is developed. Two examples are applied to validate the feasibility and efficiency of the proposed method. Results show that the proposed method is effective for non‐probabilistic reliability analysis of complex structures owning to high computational precision and low computational cost in both numerical and case study.

Hydrogen and five short-chain hydrocarbons are mixed with RP-3 aviation kerosene (RP-3) to study their blending effects on the combustion of RP-3. Seven combustion characteristics, the ignition delay time, burnout time, adiabatic flame temperature, extinction temperature, rate of production of hydroxyl radicals, laminar flame speed, and extinction strain rate, are simulated in four different reactors. The simulated data are preprocessed to match the requirements for a variation disturbance method proposed in this paper, and then the disturbance is obtained for representing the total influence of hydrogen and five short-chain hydrocarbons blending on the combustion properties of RP-3. The results show that H2, CH4, and C2H4 have a greater degree of disturbance to RP-3. In contrast, the influence of C3H6 is the weakest. The rate of disturbance shows that H2 and C2H4 have a positive effect on each of the combustion characteristics, and especially, C2H4 plays a promoting role in the combustion performance of RP-3. The reaction paths of seven fuels are analyzed by time-integrated element flux analysis, and the viability and rationality of the variation disturbance method are supported by the calculation of branching ratios of six main reaction channels.

This paper proposes a revised variation disturbance method to provide valuable information and reference for fuel design or optimization of internal combustion engines to realize the comprehensive and quantitative evaluation of the effects of blending agents on the combustion performance of primary fuels. In this method, methanol and ethanol are blended into gasoline to form six kinds of alcohol–gasoline (E10, E20, E30, M10, M20, and M30). Then, the ignition delay, adiabatic flame temperature, component concentration, fuel-burning rate, extinction strain rate, and CO emission of gasoline and alcohol–gasoline are studied by system simulation in a wide range of operating conditions. Based on the new variation disturbance method, the effects of methanol and ethanol on the combustion performance of gasoline are next analyzed globally and characterized quantitatively. The comprehensive results of ethanol and methanol on the gasoline’s combustion are visually presented. The method proposed in this paper is preliminarily validated based on the analysis of the microscopic mechanism of combustion. The results show that the blending of ethanol and methanol has positive effects on gasoline combustion, and ethanol can rapidly ignite the gasoline in a wide range of operating conditions and is superior to methanol in terms of fuel combustion, stability, and pollutant discharge. Based on the treatment of simulated values of six combustion characteristics selected in this paper and the calculations of the variation disturbance method, the total disturbance values of ethanol and methanol to gasoline combustion are obtained as 0.8493 and 0.2605, respectively. That is, ethanol has a more significant effect on improving the combustion performance of gasoline than methanol. In addition, based on the analysis results of the combustion, it is found that the blending of ethanol enlarges the reaction of notable components in gasoline. This finding also proves the effectiveness and validity of the scientific method utilized in this paper.

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