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Autoignition characteristics of a four-component surrogate fuel(M2) were investigated in a heated rapid compression machine over a wide range of conditions. The near-term light surrogate M2 developed for marine diesel fuel was formulated in our previous study containing 17.3% n-hexadecane, 5.93% 2,2,4,4,6,8,8-heptamethylnonane, 30% decalin and 46.77% 1-methylnaphthalene by mole fraction. Ignition delay times (IDTs) of gas-phase M2/N2/O2 mixture were measured at pressures of 7, 10, 15 and 20 bar over the temperature range from 675 K to 914 K for the equivalence ratios (ER) of 0.5, 1 and 1.5. NTC behaviours within the temperature of 730–850 K and two-stage ignition phenomena were observed. The effects of operating conditions such as pressure, equivalence ratio and oxygen content were systematically studied, and correlations of total IDTs and first-stage IDTs were performed to further quantitatively reveal the IDTs dependence on the above parameters. Reasonable modifications were made to a literature mechanism to improve its predicting quality. The simulation results using the modified model could satisfactorily reproduce the IDTs under the test conditions, and the model is also able to capture the ignition delay dependence on pressure and fuel/oxygen content. A brute force sensitivity analysis at the low temperature (680 K) and the NTC temperature (780 K) was carried out to identify the key reactions that govern the ignition event of surrogate M2.

Methanol is an attractive oxygenate increasingly used as primary fuel for dual-fuel combustion technology yielding beneficial thermal-efficiency and emissions in modern engines. As such, it is significant to fundamentally understand the autoignition behavior of methanol/diesel mixtures. This study measured the ignition delay times (IDTs) of methanol/diesel blends with different mixing ratios (30%, 50%, 70% methanol by mol.) on a heated shock tube and a heated rapid compression machine at temperatures of 650−1450 K, pressures of 6−20 bar, and equivalence ratios of 0.5, 1.0 and 2.0. The typical two-stage ignition characteristics with the negative temperature coefficient response were observed for dual-fuel mixtures. In general, both the total and first-stage IDTs decrease with the increment of pressure and equivalence ratio as well as diesel proportion in mixtures. The simulation results performed with a published detailed mechanism in conjunction with a tri-component diesel surrogate demonstrate generally good agreement with the experimental data at all test conditions. Moreover, a crossover of IDTs occurs at a higher temperature (~1500 K) for varying equivalence ratios, and experiment and simulation both exhibit a non-linear mixing effect of methanol addition on diesel ignition. Interestingly, simulation results clearly suggest a crossover (~940 K) for mixtures with varying methanol content at an intermediate-temperature, where the IDT of the mixture with a lower methanol ratio becomes longer as the temperature is higher than that of the crossover. Furthermore, brute-force sensitivity analyses assisted with reaction path analysis were conducted to gain deeper insights into the autoignition chemistry of dual-fuel mixtures, especially for the chemical interaction between both fuels during the low-temperature oxidation process. It is found that methanol hardly generates •OH, whereas •OH is mainly produced by the low-temperature reaction pathways of diesel. Thus, •OH is the bridge for both fuels during the ignition process. At the high methanol ratio, the H-abstraction of diesel is mainly via •HO2 while CH3OH consumes a large percentage of •OH. Consequently, the competition between methanol and diesel for •OH radicals inhibits the overall reactivity of reaction network. In addition, the original data reported here lay a foundation for the development and validation of more accurate and robust dual-fuel kinetic schemes.

Effects of liquid fuel composition variations on characteristics of self-excited thermo-acoustic instabilities in a lean premixed, pre-vaporized gas turbine model combustor were experimentally studied. Test fuels included practical RP-3 jet fuel and its blending with iso-octane and n-dodecane, which were branched and linear alkanes respectively. Under the test conditions, dynamic pressure measurements indicated that the dominant instability frequency was highest for RP-3 flame, while RP-3/n-dodecane flame exhibited the strongest instability strength. A further analysis showed that the instability frequency correlated well with the profiles of adiabatic flame temperature, and the strength of the instability highly depended on the ignition delay times of the fuels. Measurements of the flame structure and flow field with OH* chemiluminescence (CL) imaging and two-dimensional particle image velocimetry (PIV) techniques indicated that changes in the fuel composition did not alter the unstable modes and general sequences of flame-flow structure oscillations. Further power spectra and proper orthogonal decomposition (POD) analysis suggested that axial oscillations along with precessing vortex core (PVC) induced helical motion predominated periodic flame structure and flow field oscillations.

Detailed high-fidelity kinetic models of fuels are of great significance by providing guidance for the improvement of the combustion performance in engines and promising the reduction of design cycle of new concept combustors. However, the kinetic modeling works on Chinese RP-3 kerosene, the most widely used civil aviation fuel in China, are meager to date. In this study, a kinetic model, including a surrogate fuel and its combustion kinetic mechanism, were developed to describe the combustion of RP-3. Firstly, a surrogate comprised of components n-dodecane, 2,2,4,6,6-pentamethylheptane (PMH), n-butylcyclohexane and n-butylbenzene (22.82/31.30/19.19/26.69 mol%) was proposed based on the combustion property target matching method. These components are all within the typical molecular size (C10-C14) of jet fuels and thereby can potentially improve the ability of the surrogate in emulating the properties that depend on molecular size. Experiments were then carried out in a heated rapid compression machine and a heated shock tube to evaluate the performance of the surrogate in reproducing the combustion behavior of the target fuel over wide conditions. It is found that the surrogate can reproduce the autoignition characteristics of RP-3 very well. A chemical kinetic mechanism was developed to describe the oxidation of this surrogate. This mechanism was assembled using a published n-butylbenzene sub-mechanism and our previous sub-mechanisms for the other pure components, and was assessed against the present experimental data. The results showed that the simulations agreed well with the experimental data under the investigated conditions, demonstrating that the composition of the surrogate and its mechanism are appropriate to describe the combustion of RP-3. The first-stage ignition negative temperature coefficient behavior and the evolution of key radicals were investigated using the kinetic model.

Butanol/diesel blend is considered as a very promising alternative fuel with agreeable combustion and emission performance in engines. This paper intends to further investigate its autoignition characteristics with the combination of a heated rapid compression machine (RCM) and a heated Shock Tube (ST) to acquire a wide temperature region view. The ignition delay times (IDTs) of mixtures of 20% blending (by vol.) of n-butanol to China Stage-VI diesel, referred to as N20, were studied under the pressures of 6/10/15 bar, the equivalence ratios of 0.5–2.0, and a broad temperature range of 670–1300 K. Typical two-stage ignition and NTC behavior of the fuel were identified, and the IDT dependences on the compressed pressure, fuel/oxygen fraction, and the blending ratio were explained thoroughly and quantitively with correlation formulas. Furthermore, this paper expands the study to the effects of butanol structures. Autoignition characteristics of mixtures of 20% blending (by Vol.) of each of the four butanol isomers with neat diesel were investigated experimentally and numerically. The CRECK model was validated against the experimental results and critical reactions controlling fuel ignition were identified for further optimization.

Blending diesel and gasoline is a promising way to stabilize combustion process and reduce emissions of NOx and soot in the Homogeneous Charge Compression Ignition (HCCI) engine. In order to computationally study diesel/gasoline blends for their autoignition characteristics, a five-component diesel surrogate (21.6% n-hexadecane, 15.5% n-octadecane, 26.0% isocetane, 20.7% 1-methylnaphthalene, 16.2% decalin, by mol.) and a five-component gasoline surrogate (11.0% n-heptane, 30.8% isooctane, 38.2% toluene, 10.3% diisobutylene, 9.7% cyclohexane, by mol.) are blended in three volume ratios of 30%/70%, 50%/50%, and 70%/30% (denoted as SD30, SD50, and SD70) to compare measured ignition delay with published data of diesel/gasoline blends. A heated shock tube and a heated rapid compression machine (RCM) are used to measure the ignition delay of three surrogate blends under compressed pressures of 6, 10, and 20 bar for fuel-lean (ϕ = 0.5), fuel-rich (ϕ = 1.5), and stoichiometric mixtures. Experimental results indicate that surrogate blends match well with fuel-lean and stoichiometric diesel/gasoline/air mixtures while get longer ignition delays for the fuel-rich case, which is thought of as the consequence of fitting the surrogate to fuel-lean conditions in the engine. The kinetic simulation for ignition delays is performed with a comprehensive mechanism. Due to the mechanism overpredicting ignition delays in the intermediate-to-high temperature region, proper refinement is done to the original mechanism based on sensitivity analyses at 1000 and 660 K. A further comparison of ignition delay predictive ability for two mechanisms is conducted subsequently. The modified mechanism not only simulates ignition delays in the intermediate-to-high temperature region successfully but also maintains the good performance of the original mechanism in the negative-temperature-coefficient (NTC) and low-temperature region. Besides, species and temperature profiles after the compression stroke in RCM are simulated using the modified mechanism for three surrogate blends at equal equivalence ratio, compressed pressure, and compressed temperature. Sensitivity analysis is also conducted to identify reactions dominating the system reactivity.

This work presents new fundamental combustion experimental datasets and propose an improved kinetic model for n-dodecane, a widely used surrogate component for jet fuels and diesel. In the experiments, ignition delay times for n-dodecane, were measured over low-to-high temperature range by combining a heated rapid compression machine (RCM) and a heated shock tube (ST). The measurements cover a wide range of temperatures (621–1320 K), pressures (8, 15 bar) and equivalence ratios (0.5–1.5). Flow reactor oxidation was also carried out over temperature range of 600–1100 K and at equivalence ratios of 0.5, 1.0 and 1.5 under atmospheric pressure to provide species evolution profiles of O2, CO, CO2 CH4, C2H4 etc. These datasets were used to develop a mechanism for n-dodecane. New rate coefficients were adopted from recent literature to improve the performance of the model, leading to a model composed of 737 species and 3629 reactions. The present experimental data, as well as a wide range of datasets in literature, were used to evaluate the performance of the model. An overall good agreement of the predictions with the experimental results was observed. This model is anticipated to facilitate the development of kinetic models for jet fuel surrogate.

Digital twin (DT) technology is essentially the equivalent mapping of the physical world in the digital space, and is therefore also considered to be a central technology to realize cyber-physical systems (CPS). Traditional DT implementations suffer from data diversity and lack of efficient visual human-machine interface while mixed reality (MR) technology provides a new possibility due to its powerful immersion and interactivity. In this paper, we propose an MR-based DT implementation approach for the flexible manufacturing system (FMS) design. Discrete event simulation model and mixed reality scene are applied to enable multiple users to collaboratively evaluate and optimize design schemes in a dynamic simulation way and an immersive and interactive environment respectively. In this approach, an improved particle swarm optimization algorithm is used to solve the facility layout problem which is one of the core problems of FMS design. Furthermore, the DT created in the design stage, which is a virtual representation of the physical FMS, can be extended to the whole FMS lifecycle, including the manufacturing and service stages. A case study of application on a real FMS is presented to illustrate the advantage of this approach.

2,2,4,6,6-pentamethylheptane, a highly branched alkane, is a promising component candidate of branched alkanes in the surrogates for jet fuels and a major component in alternative fuels. In spite of its great relevance and importance in real fuels, it has only attracted very little interest. This work provides a new set of experimental data and a newly proposed detailed kinetic mechanism for this hydrocarbon. In the experiments, the autoignition characteristics of 2,2,4,6,6-pentamethylheptane, was measured in a rapid compression machine and a shock tube spanning over the equivalence ratios of 0.5, 1 and 1.5, pressures of 15 and 20 bar and temperature range of 603–1376 K. The dependence of ignition delay times on pressure, mole fraction of fuel, mole fraction of oxygen and dilution ratio were systematically investigated. Negative temperature coefficient (NTC) behavior was observed during the autoignition event, but the NTC temperature window was found to be much lower than the counterpart normal paraffin. A detailed kinetic model containing 729 species and 3390 reactions was proposed to describe the combustion behavior of this compound over low-to-high temperature range. The model was validated against the present experimental data, as well as the limited datasets in literature. Good agreements were observed between the experimental data and the predictions from the proposed model. Kinetic analyses, including sensitivity analysis and reaction pathway analysis, were carried out to provide insight into the combustion characteristics from the kinetic perspective. Comparisons were also carried out with the datasets for other branched alkanes and normal-paraffin with same carbon numbers over the same conditions to reveal the effects of the molecular structure.

A good knowledge of the reaction kinetics of n-butylcyclohexane, a widely used surrogate component for jet fuels and diesel, is crucial for understanding the combustion chemistry of practical fuels. This paper proposes a detailed kinetic model consisting of 1802 species and 7246 reactions to describe from low to high temperature chemistry of n-butylcyclohexane. The autoignition and oxidation of this fuel were investigated over a wide range of conditions. Ignition delay times were measured at 10, 15 and 20 bar for equivalence ratios of 1 and 1.5 under highly diluted conditions in a heated rapid compression machine. Oxidation experiments were performed in a flow reactor for equivalence ratios of 1 and 1.5 over the temperature range of 650–1075 K at 1 atm. Several oxidation products were identified and their mole fraction profiles were measured as a function of temperature. The model was evaluated with respect to the new experimental data. Additionally, the model was compared to experimental data in the literature, including ignition delay times in both rapid compression machine and shock tube, speciation profiles in jet-stirred reactor. Good agreement was achieved with all the data. Reaction flux analyses and sensitivity analyses were performed in order to provide insight into the combustion kinetics of n-butylcyclohexane. The present model can be used to construct the kinetic models for surrogates of jet fuels or diesel, as well as to work as the starting mechanism for the development of kinetic models of larger alkylcyclohexane and bicyclic cyclohexane fuels.

The objective of the current study was to formulate RP-3 kerosene surrogate by emulating fuel properties affecting the physical and chemical processes of the target fuel under the engine relevant conditions. This study utilized two-dimensional gas chromatography with time-of-flight mass spectrometry (GC × GC-TOFMS) and 13C and 1H nuclear magnetic resonance (NMR) spectroscopy to characterize the compositional characteristics of RP-3 fuel, and various standard test methods were applied to measure the physical and chemical properties of the target fuel. Two surrogate fuels (K1, a mixture of five components and K2, a mixture of seven components) were optimally determined through a multi-property regression algorithm by matching carbon types (CTs), distillation curve, cetane number (CN), density, and threshold sooting index (TSI) of the target fuel. The measured and estimated values of both target properties and non-target properties of surrogates were validated against the experimental data of RP-3 kerosene. Ignition delay times (IDTs) of both surrogates were investigated in a heated shock tube and a heated rapid compression machine under engine relevant conditions and validated against the measured results of RP-3. Overall, K1 and K2 both exhibited good matching on the compositional characteristics, physical-chemical properties, and gas phase ignition behaviors with the target fuel. In contrast, the seven-component K2 was more competitive and more comprehensive.

Cycloalkanes with long alkylic side chains are important chemical components in diesel and jet fuels. Although with the increasing interest in their combustion chemistry, related studies are very limited. In the present study, ignition delay times were measured for n-butylcyclohexane by combining a heated rapid compression machine and a heated shock tube. The data was obtained for equivalence ratios of 0.5, 1 and 1.5, at pressures of 10, 15 and 20 bar and over the temperature range of 612–1374 K. It was found that n-butylcyclohexane displayed marked low temperature reactivity with a typical negative temperature coefficient behavior. A correlation was developed to reproduce the measured ignition delay times over the entire temperature ranges. The results showed that it can well estimate the ignition delay times in the testing conditions. The effects of operating parameters on ignition delay times, including temperature, pressure, equivalence ratio, oxygen concentration and dilution ratio, were systematically presented and discussed. In the present work, a published mechanism was tuned with some modifications and was used to simulate the autoignition of n-butylcyclohexane. This model accurately captured the effect of the operating parameters over a wide range of conditions, and the simulations were in satisfactory agreement with the experimental results. For a better understanding of the chemistry involved during the autoignition events, kinetic analyses were performed using the tuned mechanism to provide insight to the experimental results. Comparisons were also carried out with the datasets for other cycloalkanes over the same conditions to reveal the effect of the side chain, and the trends, i.e., the longer side chain contributes to the stronger low temperature reactivity, were highlighted and discussed.

In this study, a detailed chemical reaction mechanism of n-decane containing 1034 species and 4268 reactions has been reduced at three different reduction levels to study the effects of subsequent ...

Chemical composition difference widely exists in real fuels, and the composition difference will affect the fuel autoignition and heat release in HCCI-based advanced engines. This study aims to explore the composition effects on autoignition by comparing the autoignition characteristics of two commercial diesels (China Stage-V and Stage-VI). The main composition difference is that Stage-V diesel has a higher paraffin content and a lower naphthene content than Stage-VI diesel. Ignition delay times (IDTs) of the two diesels were measured in a heated rapid compression machine at equivalence ratios of 0.37–1.25, pressures of 10–20 bar, and temperatures of 687–865 K. It is found that the difference in the total IDTs of the two diesels varies with the temperature range, and the first-stage IDTs of Stage-V diesel are much shorter than those of Stage-VI diesel. The IDT discrepancies were appropriately explained using the composition difference between the two diesels. Model simulation was carried out using a ternary and a five-component diesel surrogate coupled with an updated kinetic model. Simulation results show that the composition effects on the autoignition of the two diesels can be well captured by the two surrogates, where the ternary and five-component surrogates agree well with Stage-V and Stage-VI diesels, respectively. To further reveal the intrinsic mechanism of the composition effects, low-temperature reactivity difference between the two surrogates was interpreted from a kinetic perspective. Rate of production (ROP) analysis on OH radical confirms that the addition of decalin in the five-component surrogate is primarily responsible for the longer first-stage IDT compared to the ternary surrogate. Since the two surrogates capture the composition difference and autoignition characteristics of the two diesels, the conclusion from the kinetic analysis will help understand the composition effects on the autoignition of the diesels.

Autoignition characteristics of RP-3 kerosene were investigated using a heated rapid compression machine and a heated shock tube over a wide range of conditions. Ignition delay times (IDTs) for RP-3 kerosene were measured at pressures of 10, 15 and 20 bar over a range of temperatures from 624 to 1437 K and for equivalence ratios from 0.5 to 1.5. A three-component surrogate fuel (49.8% dodecane, 21.6% iso-cetane and 28.6% toluene by mole) was proposed and a kinetic model was developed to describe the combustion chemistry of RP-3. Negative temperature coefficient (NTC) behavior was observed in the autoignition, of which the temperature range varied within 701−884 K depending on operating conditions. IDT correlations in low and high temperature regions were obtained and then the dependences of IDT on pressure, equivalence ratio, oxygen content and dilution ratio were systemically studied. Comparison between the predictions using the new model and the experimental data shows that this model can accurately describe the autoignition characteristics of RP-3. Brute force sensitivity analyses were carried out to identify the key reactions that govern the ignition event. The large experimental data set and kinetic model provided in the current work will provide insights into the understanding of RP-3 ignition.

Autoignition and oxidation characteristics of a three-component diesel surrogate fuel were studied in a heated rapid compression machine (RCM) and a flow reactor (FR) over a wide range of conditions. The surrogate components, n-cetane, 2,2,4,4,6,8,8-heptamethylnonane (HMN), and 1-methylnaphthalene (1-MN), all fall within the C10–C20 range of real diesel fuel. The RCM-measured ignition delay times (IDTs) and FR oxidation data of the surrogate fuel were then compared with those of the target diesel. It is found that the diesel surrogate fuel is in good agreement with the target diesel in total ignition delay time and FR speciation data over the whole temperature range, reflecting the success of the surrogate fuel construction. A semi-detailed kinetic model was used to predict the autoignition and oxidation behavior of the surrogate fuel in RCM and FR experiments. Results show that the kinetic model captures well the measured total IDTs and the mole fractions of O2, H2, CO2, and small hydrocarbons under all investigated conditions. To deepen the understanding of low-temperature reaction scheme, rate of production (ROP) analysis of OH and HO2 radicals was carried out during the first-stage ignition to explore the causes of low-temperature and negative temperature coefficient (NTC) reactivity. A brute force sensitivity analysis of first-stage ignition delay time was also conducted to further identify the controlling reactions in the first-stage ignition of the surrogate fuel.

The extremely complex composition of practical fuels highlights the significance of surrogate fuels for numerical simulation and experimental research in engine development. Heavy fuel oil plays an important role in ocean-going transportation but the surrogate fuels to mimic its chemical and physical properties are seldom proposed. In this study, a promising approach was utilized to formulate surrogate fuels for a widely used heavy marine diesel oil based on some important fuel physical–chemical properties. Some novel methods were applied to characterize a sample of RMG180 residual marine fuel, including GC×GC–TOFMS to characterize the composition and the simulated distillation method to characterize the volatility. Two surrogate fuels were designed for different targets: one heavy six-component surrogate was designed for premixed and spray-guided modes by emulating both real fuel’s physical and chemical properties, including the distillation curve, cetane number (CN), and liquid density at 20 °C, whereas...

Diesel/gasoline blended fuel, also named as dieseline, has attracted worldwide interests in varied advanced engine combustion modes dominated by mixing time scale and chemical reaction time scale. However, the research on ignition properties and chemical reaction mechanism of diesel/gasoline blends over wide operating conditions is still lacking. In current study, ignition delay time measurement of diesel/gasoline blends with different diesel proportion (30%, 50%, and 70% by volume) were conducted in a heated shock tube and a heated rapid compression machine (RCM) covering a broad range of temperatures between 636 and 1317 K at pressures between 6 and 20 bar for gas-phase dieseline/O2/N2 mixture at varying equivalence ratios from 0.5 to 1.5. The experimental results revealed different dependence of ignition delay time on pressure, equivalence ratio and composition at different temperatures and varying negative-coefficient (NTC) behaviors were also observed at intermediate-temperature regime. The increase in proportion of diesel led to shorter ignition delay times under all conditions, though the ignition data at high temperature only showed marginal discrepancies. Besides, a crossover of ignition data occurred at the highest temperature for varying equivalence ratios. A tertiary surrogate for diesel and a tertiary surrogate for gasoline were chosen to calculate conditions after reflected shock in shock tube and compression in RCM. Then, simulations of ignition delay time for diesel/gasoline blends were conducted using a detailed model. Finally, kinetic analyses were performed to gain insight into the ignition characteristic of diesel/gasoline blends.

Iso-cetane (2, 2, 4, 4, 6, 8, 8-heptamethylnonane) is known as a primary reference fuel for cetane number rating and is regarded as an applicable component for surrogate diesel fuel. In this study, ignition delays for iso-cetane homogeneous mixture were measured at equivalence ratios varying from 0.5 to 2.0, compressed pressures of 10, 15 and 20 bar, and compressed temperatures of 620–880 K in a heated rapid compression machine (RCM). Two-stage ignition characteristic of iso-cetane was observed for all mixtures. Negative temperature coefficient (NTC) behavior of iso-cetane ignition delay appears in the temperature range of 670–730 K, which is significantly lower than that of other large hydrocarbons. Influences of compressed temperature, compressed pressure, and mixture composition on iso-cetane ignition delays were also investigated. It is found that the total ignition delays shorten with the increase of compressed pressure, equivalence ratio and oxygen mole fraction. The first-stage ignition delays exhibit Arrhenius-like dependence on compressed temperature and are relatively insensitive to the change of other parameters. In addition, modeling study was conducted using an updated iso-cetane kinetic model developed from a literature iso-cetane mechanism. Simulation results show that the total ignition delays are underestimated while the temperature range of the NTC behavior is overestimated. Rate of production (ROP) analysis prior to the first-stage ignition was also conducted to identify the controlling reactions generating and consuming OH and HO2 radicals in low-temperature (low-T) reaction pathways.

Knowledge of the autoignition characteristics of diesel fuels is of great importance for understanding the combustion performance in engines and developing surrogate fuels. Here ignition delays of China's stage 6 diesel, a commercial fuel, were measured in a heated rapid compression machine (RCM) under engine-relevant conditions. Gas-phase autoignition experiments were carried out at equivalence ratios ranging from 0.37 to 1.0, under compressed pressures of 10, 15, and 20 bar, and within a temperature range of 685–865 K. In all investigated conditions, negative temperature coefficient (NTC) behavior of the total ignition delays is observed. The autoignition of the diesel fuel exhibits pronounced two-stage characteristics with strong low-temperature reactivity. Experimental results indicate that the total ignition delays shorten with increasing compressed pressure, oxygen mole fraction and fuel mole fraction. The first-stage ignition delays are mainly controlled by compressed temperature and also affected by oxygen mole fraction and compressed pressure but show a very weak dependence on fuel mole fraction. Correlations describing the first-stage ignition delay and the total ignition delay were proposed to further clarify the ignition delay dependence on the multiple factors. Additionally, it is found that the newly measured ignition delays well coincide with and complement the diesel ignition data in the literature. A recently developed diesel mechanism was used to simulate the diesel autoignition on the RCM. The simulation results are found to agree well the experimental measurements over the whole temperature ranges. Species concentration analysis and brute force sensitivity analysis were also conducted to identify the crucial species and reactions controlling the autoignition of the diesel fuel.

Abstract A novel methodology based on chemical deconstruction for the formulation of surrogate fuels for biodiesels was proposed, developed, and validated. Surrogates were formulated using sub-surrogates of methyl palmitate, stearate, oleate, linoleate, and linolenate, which are the major components of biodiesel. Each methyl ester sub-surrogate was constituted by a binary or ternary fuel mixture. To formulate the sub-surrogates, key physical and chemical parameters based on engine spray and combustion were considered with preferential weight functions. To calculate the optimal surrogates, novel weighted Euclidean distance and analytic hierarchy process algorithms were used to accurately determine the components and their proportions. Next, surrogates for biodiesels were assembled from the sub-surrogates according to the component ratios of the target fuels. Using this methodology, surrogates for biodiesels could be formulated regardless of feedstock origin and production region. For example, the surrogate fuel for soybean biodiesel consisted of 62.9% methyl decanoate, 15.0% n-hexadecane, 9.4% methyl trans-3-hexenoate, and 12.7% 1, 4-hexadiene in mole fractions. The process of experimental validation was divided into two steps: first, verifying the sub-surrogates for methyl palmitate, methyl oleate, and methyl linoleate; and second, comparing the quaternary surrogates with real soybean biodiesel. Point-to-point experiments were conducted on three platforms: a heated rapid compression machine, a laminar flow reactor, and an ignition quality tester. More specifically, the rapid compression machine experiments compared the autoignition characteristics, especially the low-temperature reactivity, of the surrogates and the target fuels under constant-volume adiabatic conditions. Laminar flow reactor was used to compare the low-to-intermediate oxidation properties of the surrogates with those of the target fuels, especially the early formation of olefins and carbon dioxide, which is a key characteristic of the combustion of biodiesel. Ignition quality tester was used to ensure that the surrogates had similar ignition and combustion delay times under engine-like conditions. The results of all of these experimental validations showed that the ignition and oxidation properties of the surrogates were consistent with those of their target fuels. In addition, a kinetic model of the quaternary surrogates was proposed and further validated in a laminar flow reactor. In sum, quaternary surrogate fuels were developed using a method based on chemical deconstruction, which was shown through validation experiments to be highly accurately and reliably reproduce the combustion properties of soybean biodiesel. Furthermore, chemical deconstruction method has great potential in surrogate modeling for various biodiesels.

Autoignition characteristics of decalin, a bicyclic alkane, were investigated in a heated rapid compression machine (RCM) over a wide range of conditions. Ignition delay time (IDT) was measured at compressed pressures of 10, 15 and 20 bar, for equivalence ratios of 0.5, 1.0, 1.5 and 2.0, and at temperatures in the range 631−930 K. Negative temperature coefficient (NTC) behavior of decalin ignition delay time was observed within the temperatures of 750−860 K, in which the ignition delay time increases with rising temperature. The dependence of ignition delay time on compressed pressure, equivalence ratio, and oxygen concentration was systemically studied. A reasonable modification was made to a literature mechanism. The simulation results using the tuned mechanism are found to well capture the dependence of the measured ignition delay time on temperautre, pressure, equivalence ratio, and oxygen concentration over the entire temperature range. Correlation formulas of the simulated and measured ignition delay times were proposed to quantitatively reveal the ignition delay time dependence and to evaluate the mechanism performance. A reaction pathway analysis was carried out at low temperature (700 K), NTC temperature (850 K), and high temperature (1000 K), respectively, to identify the dominant reaction pathways consuming decalin and intermediate species. A sensitivity analysis was also performed at different temperatures and equivalence ratios to find out the important reactions that promote and inhibit decalin autoignition.

Reduction of detailed mechanisms of large hydrocarbons is of significant importance to multi-computational fluid dynamics (CFD) simulations, while the scale and accuracy of the reduced mechanism are closely related to the reduction method adopted. In this study, a workbench for systematic reduction of detailed mechanism was developed. It is operated on the MATLAB platform and integrated with CHEMKIN PRO software. In the scheme, a skeletal reduction module was first employed to identify and eliminate unimportant species and associate reactions, in which four different algorithms based on directed relation graph (DRG) and its deduced methods, including single DRG, single DRG with error propagation (DRGEP), two-stage DRG, and DRG with DRGEP were applied and compared to find the optimal solution for further reduction. Then a subsequent reaction sensitivity analysis module was implemented to eliminate less important reactions. The potential and feasibility of the proposed scheme were presented with an example ...

This work proposed a kinetic model for RP-3, the most widely used military-civilian aviation fuel in China. Four hydrocarbons within the typical size of major components in RP-3, i.e., n-dodecane, iso-dodecane (2,2,4,6,6-pentamethylheptane), decalin and n-butylbenzene, were included in the component palette to improve the ability of the surrogate to mimic the properties related to the molecular weight. Seven properties, cetane number, molecular weight, H/C ratio, threshold sooting index, lower heating value, the proportion of -CH3 and -CH2 in the total carbons were selected as targets aiming at the comprehensive emulation of the chemical and physical propensities of RP-3. By sequential use of the genetic algorithm and a local search method, a surrogate containing 27.44% n-dodecane, 28.81% iso-dodecane, 26.12% decalin and 17.63% n-butylbenzene by mole was formulated. The autoignition delay times of the surrogate were measured using a heated rapid compression machine at pressures of 10, 15, 20 bar and equivalence ratios of 0.5, 1.0 and 2.0 over low-to-intermediate temperature range. Results show that the surrogate can not only emulate the target properties but also the key non-targeted properties. A kinetic model of 3065 species and 11,898 reactions was then developed based on the proposed surrogate to describe the chemical process during the combustion of RP-3. Simulations show that the model can predict the fundamental combustion datasets in the present work and literature satisfactorily, suggesting the rationality and applicability of the model. Rate of production and evolution histories of OH and HO2 were then conducted using the kinetic model to provide insight into the combustion of RP-3. Analysis suggests that negative temperature coefficient behavior also exists in the first stage ignition.

Natural gas/diesel dual-fuel (DF) combustion technology has attracted substantial attention in terms of thermal-efficiency improvement and emission reduction in advanced compression ignition engines. As known, autoignition behavior of DF mixtures plays a significant role in controlling the ignition timing and combustion performance in engines. In the present study, ignition delay time (IDT) measurements of methane/diesel mixtures with three varying diesel substitution ratios (denoted as DSR30, DSR50, and DSR70) were conducted on both a heated rapid compression machine and a heated shock tube under wide-range conditions (T = 640–1450 K, p = 6–20 bar, ϕ = 0.7, 1.0, and 2.0 in ‘air’ mixtures). Experimental results show that DF blends exhibit typical two-stage autoignition characteristics along with the negative temperature coefficient (NTC) response at the temperature region currently investigated, owing to the addition of high-reactivity diesel fuel. Moreover, both the total and first-stage IDTs decrease with the rise of pressure and equivalence ratio as well as diesel substitution ratio. Additionally, a crossover of IDTs occurs at a high temperature (~1400 K) for varying equivalence ratios, and there exists a non-linear promoting effect of diesel contents on IDTs. The simulation results performed using a detailed chemical kinetic mechanism (POLIMI_1412) in conjunction with a well-validated tri-component diesel surrogate show generally good agreement with the experimental results at the current test conditions. Furthermore, species evolution assisted with brute-force sensitivity analysis was carried out to further understand the autoignition chemistry of the DF mixture, particularly the chemical interplay between methane and diesel during the low-temperature ignition processes. It is found that methane hardly generates OH radicals, which are mainly produced via the low-temperature oxidation pathways of diesel fuel. The competition between methane and diesel for OH radicals inhibits the consumption of diesel while promotes the depletion of methane, resulting in an inhibiting impact on the overall reactivity of the reaction system. What's more, the experimental data reported herein provide a foundation for the development of DF kinetic models with high accuracy and robustness.

Autoignition characteristics of methane/diesel mixtures with diesel fractions of 5%, 15%, and 30% were investigated in a heated shock tube over temperatures of 960–1500 K, pressures of 6–20 bar, and equivalence ratios of 0.5, 1.0 and 2.0. Generally, ignition delay times (IDTs) decrease with increasing reflected-shock pressure or diesel content. The total equivalence ratio exhibits a slight influence on IDTs, whereas a crossover for IDTs occurs at a higher temperature from fuel-lean to fuel-rich conditions. Besides, three mechanisms in conjunction with a well-validated diesel surrogate were used to predict the IDTs of dual-fuel mixtures. Mech-3 (CRECK-2003) demonstrates the best performance under all test conditions based on quantitative error analysis. Moreover, there is a nonlinear mixing effect for methane/diesel mixtures. The IDT-reducing effect of diesel to methane is more pronounced compared to n-heptane, especially at intermediate-temperatures. Furthermore, the impact of diesel-addition on methane ignition was explored with kinetic analyses including species evolution, brute-force sensitivity analysis and rate of production analysis. These active radicals produced at the initial stage, especially for H radicals rapidly generated through the decomposition of diesel, readily trigger H-abstraction reactions on CH4, resulting in the continuous production of H from HCO decomposition and eventually triggering the hot-ignition via the chain-branching reactions of H + O2 = O + OH and H2 + O = H + OH. Consequently, the main reason for the IDT-reduction by diesel-addition at the high temperature is the rapid decomposition of diesel to produce H during the initial ignition period.

Iso-cetane (2,2,4,4,6,8,8-Heptamethylnonane) is used as a reference fuel to define the cetane number rating of diesel fuel and as an important component for diesel and jet fuel surrogates. This experimental study presented the ignition delay measurement of iso-cetane in a heated shock tube at a temperature range of 838–1617 K, pressures of 10, 15, and 20 bar and over equivalence ratios of Φ = 0.5–2.0 with fuel/air mixture and at Φ = 1.5 with diluted fuel mixture. The experimental conditions were designed to study the effect of pressure, equivalence ratio, and oxygen concentration variation on ignition delay times. The ignition delay time was found to be sensitive to all the investigated factors. The experimental data obtained were in good agreement with both low and high-temperature data reported in the previous studies. The comparison with experimental data of iso-alkanes of various chain lengths showed an impact of chain length on reactivity noticeably at intermediate and low temperatures. The onset of the negative temperature coefficient region is also found to be influenced by an increase in the chain length. The mechanism of Yu et al. was revised by incorporating new rate rules. The kinetic modeling predictions of the updated model showed a noticeable improvement in the mechanism performance except under diluted conditions. The reaction flux and sensitivity analyses were conducted to further discuss the mechanism performance and overall kinetic behavior of the fuel.

Ammonia (NH3) is gaining increasing interest as a carbon-free alternative fuel in engine systems. Co-firing NH3 with diesel can overcome the high auto-ignition temperature and narrow flammability limits of pure NH3, while exploit its advantage. This study presents the auto-ignition properties of NH3/diesel binary fuel, at various NH3 blending ratios (10%, 30% and 50%) in a rapid compression machine. Ignition delay times (IDTs) were measured spanning a temperature range of 670–910 K, pressures of 10–20 bar, and equivalence ratios of 0.5–1.5. Typical two-stage ignition and negative temperature coefficient (NTC) response were identified for the blends. Both the first-stage and the total IDTs increase with the increasing NH3 blending ratio, and there exists a non-linear inhibiting effect of NH3 fraction on IDT. A blending mechanism was then constructed based on the existing diesel mechanism and NH3 mechanism. The mechanism can predict the inhibiting effect of NH3 addition, but fails to well capture the IDTs over the whole temperature range, especially for the first-stage IDT and the NTC response. Further kinetic analysis, including species mole fraction history, brute force sensitivity analysis and reaction pathway analysis, were conducted to gain deeper insight into the auto-ignition chemistry of the blending fuel. These analyses suggest the rate parameters of reactions NH3 + OH ⇒ NH2 + H2O and NH2 + NO ⇒ N2 + H2O are critical to accurately predict IDTs, and the competition role of NH3 for OH radical inhibits the diesel low-T chain-branching sequence, which eventually leads to restraining the reactivity of the whole reaction system.

In this paper, combustion stability characteristics of a laboratory-scaled lean premixed prevaporized gas turbine model combustor operated with different liquid fuels were experimentally examined. Test fuels involved one linear alkane (n-dodecane), one branched alkane (iso-octane), one cyclic alkane (methylcyclohexane (MCH)) and practical multi-component RP-3 jet fuel. Tests conducted under a wide range of equivalence ratios ( ∅ ) and inlet air velocities suggested that n-dodecane flame featured the smallest ( ∅ = 0.34 ) lean blow out (LBO) limit, while iso-octane flame was characterized by the highest ( ∅ = 0.39 ). On the other hand, n-dodecane flame shifted from stable to unstable combustion at the highest equivalence ratio ( ∅ = 0.52 ), which is ~18% higher than the lowest case RP-3 ( ∅ = 0.44 ). Additional flame and flow dynamics were characterized by simultaneous high-speed OH* chemiluminescence (CL) imaging and planar particle image velocimetry (PIV) measurements. Results suggested that the instability frequency and amplitude were dependent on the fuel type and could be well related to their fundamental combustion properties. Moreover, both phase-averaged and time-resolved OH* CL imaging and PIV results demonstrated that the global unsteady flame and flow dynamics were similar for different fuels. However, a time-lag behavior was observed when iso-octane and MCH flames were subject to similar acoustic pressure oscillations in the combustor. This was speculated to be dominantly caused by their distinct ignition delay times (IDTs), which resulted in different phase lags between heat release rate and acoustic pressure oscillations. Such findings were further supported by proper orthogonal decomposition (POD) analysis performed on the simultaneously recorded OH* CL and PIV measurements.

Tetralin or 1,2,3,4-tetrahydronaphthalene (C10H12) is a naphthenic-aromatic hydrocarbon. It is also adopted as a component for the formulation of transportation fuel surrogates. In this study, the ignition delays of tetralin/air mixtures are measured in a heated shock tube at moderate to high temperatures ranging from 830 to 1380 K, at pressures of 6, 10, 20 bar and under fuel-lean, stoichiometric and fuel-rich conditions. The dependence of ignition delays on temperature, pressure and equivalence ratio is analyzed and a four-parameter correlation is developed. The mechanism in current form showed less reactivity as compared to the experimental data. It is, therefore, modified by adjusting the rate constants of most sensitive reactions at both high and low temperatures. The mechanism showed noticeable improvements at low temperatures and high pressures. The sensitivity analyses are conducted to identify the reactions governing the fuel ignition under different pressures and equivalence ratios. The important reaction pathways are identified at both low and high temperatures to understand the underlying chemical kinetics.

This study is devoted to investigate the characteristics and kinetics of biomass tar cracking in a micro fluidized bed reactor for liquids (MFBRL). The carbon balance and conversion were measured to estimate the performance of MFBRL, and the results showed good reproducibility and reliability. H2, CH4 and CO comprised the vast bulk of the producer gas and the total volume fraction of them increased from 69.85% to 93.62% (973–1173 K). Kinetic parameters, including reaction order, pre-exponential factor and apparent activation energy, were studied with the isothermal method. The reaction orders varied greatly with temperature, suggesting that temperature significantly affected the reaction mechanism. The pre-exponential factors for H2, CH4, CO and gas mixtures were in the range of 2.37 × 103 to 2.87 × 105 S−1, while the apparent activation energies ranged from 62.96–100.2 kJ mol−1. Compared to the fixed bed experiments, the derived results were obviously higher, indicating the kinetic parameters were more suitable for describing the intrinsic reactions.

Based on three-component gasoline surrogates and five-component diesel surrogates, the effects of fuel reactivity of port injection fuel and direct injection fuel on combustion and emission characteristics of reactivity controlled compression ignition (RCCI) mode were systematically studied. The research octane number of port injection fuels and cetane number of direct injection fuels were modulated by changing the proportions of n-alkanes and iso-alkanes in surrogates. The results show that both the cetane number of direct injection fuel and research octane number of port injection fuel played the key role in the combustion phase of RCCI mode. When port injection fuel with research octane number ≤ 90, the low temperature heat release would occur. For premixed ratio of 0.8 and with RON70/CN55 as fuel, the CO emissions were the lowest (as low as 1585 ppm). Increasing the premixed ratio was an effective solution for suppressing NOx and particulate matter emissions. For premixed ratio increased from 0.4 to 0.8, the peak value of nuclear mode particulates decreased from 109 to 107. Increasing the cetane number of direct injection fuels or lowering the research octane number of port injection fuels inhibited the emissions of formaldehyde, acetaldehyde, ethylene, propylene, acetylene and 1,3-butadiene effectively. Port injection of low research octane number was beneficial to reducing indicated specific fuel consumption. Fuel combination with port injection of RON70, direct injection of CN55 and premixed ratio of 0.8 was recommended taking into account of fuel consumption, and regulated/unregulated gas emissions.

Ignition delay time (IDT) measurements of gas-phase diesel fuel were measured in a heated shock tube, covering the temperatures of T = 901–1371 K, equivalence ratios of ϕ = 0.37–1, and dilution molar ratios of N 2 /O 2 = 3.76–8.52 under three pressures of 6, 10, 20 bar. Within the temperature range investigated, the increase in pressure showed a negative effect on the IDT, and same effect was observed with the increase in concentration of fuel and oxygen. On the contrary, the increase in dilution molar ratio N 2 /O 2 directly lead to the reduction in the reactivity of the whole reaction system. Interestingly, convergence and divergence of IDT for different fuel and oxygen concentrations respectively was observed from the experimental results. The five kinetic models consisting of three kinetic mechanisms and three diesel surrogates were utilized to simulate the experiments of diesel fuel under the proposed test conditions. As compared to the other four models, Model 2 performed effectively in replicating the measured IDTs. The profile modeling of temperature and species with time was carried out at temperatures of 800 K and 1000 K on the basis of Model 2. The model indicated a two-stage ignition behavior at 800 K while only a single-stage ignition at 1000 K. The accuracy of mechanism and surrogate was found to be jointly influenced by the performance of the kinetic model. The experimental results in present study expand the test conditions of interest and provide benchmark ignition delay database of diesel fuel needed for development and validation of surrogate models.

The co-pyrolysis characteristic of biomass and lignite were investigated in a Micro Fluidized Bed Reaction Analyzer under isothermal condition. The synergetic effect was evaluated by comparing the experimental gas yields and distributions with the calculated values, and iso-conversional method was used to calculate the kinetic parameters of formation of each gas component. The results showed that synergetic effect was manifested in co-pyrolysis. For the range of conversion investigated, the activation energies for H2, CH4, CO and CO2 were 72.90 kJ/mol, 43.90 kJ/mol, 18.51 kJ/mol and 13.44 kJ/mol, respectively; the reactions for CH4 and CO2 conformed to 2 order chemical reaction model, and for H2 and CO conformed to 1.5 order chemical reaction model; the pre-exponential factors for CH4, CO2, H2 and CO were 249.0 S−1, 5.290 S−1, 237.4 S−1 and 2.693 S−1, respectively. The discrepancy of the kinetic parameters implied that there were different pathways for forming the different gas.