Fuel Communications最新文献

Laminar flame speed (LFS) is a key physicochemical property of a premixed fuel/oxidizer mixture, and is critical in the description of complex combustion phenomena. Accurate experimental measurements of LFSs for various fuels have been performed to develop and validate detailed kinetic mechanisms, which in turn are used to predict LFSs under various combustion conditions. However, such procedure is inefficient, especially in large-scale turbulent combustion modeling studies. Based on previous experimental studies of LFSs for various fuels, this work aims to develop a data-driven machine learning (ML) model for the prediction of LFSs of hydrocarbon and oxygenated fuels. Descriptors computed from semi-empirical quantum chemistry methods are used as input in ML models due to the simplicity and computational-efficiency. Pearson correlation analysis is used to select important features, and 5 descriptors are screened as the input features for ML model development. The accuracies and interpretabilities of existing 16 ML algorithms in the prediction of LFSs are compared through systematically evaluated the errors based on the differences between experimental data and model prediction. These ML models include regression trees, support vector machine regression, gaussian process regression, and ensemble trees. An efficient ML model for predicting LFSs of hydrocarbon and oxygenated fuels based on gaussian process regression algorithm is proposed, which exhibits good accuracy in predicting of LFSs for variable pressure, temperature, and equivalence ratio. The dependency of LFSs on the descriptors are also analysed. The developed ML model is fast enough for integration into large-scale computational fluid dynamics for combustion studies.

Using an in-house 0D plasma chemical solver, this paper investigates the species involved in plasma-assisted reforming of both pure ammonia and stoichiometric ammonia-air mixtures. A nanosecond repetitively pulsed plasma is simulated for dielectric barrier discharge conditions, with reduced electric fields of 180 and 360 Td, energies per pulse of 0.5 and 1 mJ/cm³, and pulse repetition frequencies up to 500 kHz. To show the effect of reforming on combustion performance, the reformates are fed into a neutral species combustion chemistry solver to calculate the ignition delay time at gas-turbine relevant conditions. For a reformed stoichiometric mixture, it is possible to achieve a reduction of two orders of magnitude in ignition delay time. This reduction, however, comes at the cost of lost enthalpy, as ammonia reacts with oxygen to create water. Path flux and sensitivity analyses were performed, and it as found that the two most crucial species in the reformate were H₂ and NH₂. The presence of NH₂ in high concentration also resulted in lower concentrations of NO after ignition, compared to the unreformed mixture. When reforming pure ammonia, the same number of pulses and energy as in the stoichiometric case reduce ignition by one order of magnitude. A higher reduction is possible with more pulses, unlike the stoichiometric reforming case in which ignition is reached during the reforming process, and with no loss of enthalpy due to oxidation. At 200 kHz, a reduction of two orders of magnitude is possible after 1500 pulses. These results support the feasibility of plasma-assisted reforming for the improvement of ammonia combustion characteristics at relevant conditions.

The work investigates the suitability of a multi-component hydrocarbon fuel, namely HCF-1, as a potential fuel-cum-coolant for space vehicles under supercritical environments. The effects of reactor temperature, space-time, and initiator loading on fuel conversion, coke deposition, heat sink capacity, and gas selectivity are examined. The obtained value of fuel conversion, coke deposition rate, and chemical heat sink at 680 °C and 55 bar pressure are 10.3 wt.%, 7 mg/min, and 805 kJ/kg, respectively. The increase of fuel space-time from 2.8 s to 8.5 s increased the endothermicity by about 1.8-times. A decreasing trend in the olefin-to-alkane ratio with temperature and space-time is observed. The microscopic analysis confirmed the presence of both spherical-shaped (amorphous) and ribbon-like (filamentous) structures in the coke deposits. The estimated value of the apparent activation energy of the HCF-1 cracking reaction is 125 kJ/mole. Tributylamine (TBA) is recognized as a potential initiator to improve the cracking characteristics of the HCF-1. The fuel conversion and endothermicity increased by 58% and 18%, respectively, in the presence of 10,000 ppm of TBA at 650 °C. From the investigation, it can be said that the HCF-1 has a good potential to act as an endothermic fuel.

In view of reducing greenhouse gas emissions the transition from fossils fuels to sustainable energy carriers is a prerequisite to keep global warming within tolerable limits. Since IC engines will continue to play a role in global energy strategies during a transitional phase, especially for large engine applications difficult to electrify, the use of ammonia as substitute fuel may be an approach for decarbonization. However, its utilization needs research since ignition concepts and combustion properties still pose considerable challenges in view of reliable and efficient operation. A new "optical engine" test facility ("Flex-OeCoS") has been successfully adapted enabling dodecane pilot fuel ignited premixed ammonia dual-fuel combustion investigations. It features IC engine relevant operation conditions such as pressures, temperatures, and flow (turbulence) conditions as well as adjustable mixture charge composition and pilot fuel injection settings. In parallel, thermodynamic heat release analysis in terms of ignition and combustion characteristics was performed. Simultaneously applied high-speed Schlieren/OH* chemiluminescence measurements supported the examination of the combustion process. Initially premixed ammonia dual fuel combustion has been compared to a representative methane combustion process in terms of different gas properties (lower heating value, air-fuel ratio) which illustrates its lower reactivity affecting heat release and flame propagation. Moreover, ignition delay, combustion transition, and turbulent flame propagation as well as heat release characteristics have been investigated for premixed ammonia dual-fuel combustion within variation of air-fuel equivalence ratio, start of pilot fuel injection, and pressure/temperature operation conditions. The results illustrate strong dependency on air-fuel equivalence ratio (energy content) and temperature conditions in terms of ignition delay, dual-fuel combustion transition, and corresponding heat release. The optical investigations confirm the thermodynamic analysis and promote assessment of pilot fuel evaporation, ignition, combustion transition, and flame propagation. Conclusions give extended insight into the thermo-chemical processes of ammonia pilot fuel ignited dual-fuel combustion. The acquired data may also support further development of numerical CRFD methods.

Biofouling of gasoline can occur during fuel storage caused by bacteria and fungi that form a biofilm at a fuel/water interface and that produce organic acids and sulfides. Fuel additives are applied to gasoline to prevent biofouling but are relatively expensive, are not always effective against biofilms, and do not contribute to the combustibility of gasoline. Bio-isobutanol is an approved, certified advanced biofuel and is added up to 16% (v/v) in gasoline blends “iBut16”; n-butanol blends are currently under review. Microorganisms are inhibited by n-butanol or isobutanol when the aqueous concentration reaches >2-3% (w/v). We determined that n-butanol partitions into the aqueous phase of a model gasoline/water system reaching concentrations of 42 g/L and up to 48 g/L from gasoline blends at 10% and 24% (v/v), respectively. Likewise, isobutanol blended in gasoline at 10% and 24% (v/v) partitioned into an aqueous phase at 45 g/L and 53 g/L, respectively. Several bacterial and fungal strains that originate from fuel storage tanks, or are known to be solvent tolerant, were evaluated for their potential growth in a range of n- and isobutanol concentrations. Growth rates for all strains tested were reduced by 40–100% relative to untreated controls in n- and isobutanol concentrations of 1.5 and 2.0% (v/v). No observable growth occurred for any of the microorganisms in solvent concentrations at 3.0% (v/v). T amphiphilic and chaotropic properties of n- or isobutanol help them inhibit microbial growth and could serve as effective biocides during fuel storage as well as being valuable fuel additives.

This study investigates the physicochemical behavior of Wheat Straw and Groundnut Stalk biomass and its impact on the thermal behavior during torrefaction process. The torrefaction was experimentally investigated by thermogravimetric analysis (TGA) at five isothermal heating rates of 20, 30, 40 and 50 °C/min. Results revealed that during the torrefaction process, significant fraction of hemicellulose and volatile content reduces that improves the high heating value. The results indicated that torrefaction treatment improved the fuel properties with elevated torrefaction temperature, including the lower volatile content, higher carbon content, and higher heating value. Kinetic parameter analysis indicated that the Ozawa–Flynn–Wall and Starink model were significant in calculating the activation energy, and the average activation energy was 240 kJ/mol and 238 kJ/mol (Wheat Stalk and torrified wheat Stalk) 127 kJ/mol and 129 kJ/mol (Groundnut Stalk and torrified Groundnut Stalk). An excellent linear relationship between lnA and E_α was observed, indicating that the compensation effect existed between the E_α and lnA during torrification. These results provide important basic data support for the thermochemical conversion of cornstalk to energy and chemicals.

This work presents an experimental study on the thermal conductivity, viscosity, flash point and fire point of kernel palm oil methyl esters (KPOME) in the presence of conductive magnetic nanoparticles (FeO₃). The mass concentration of FeO₃ ranges from 0,10 wt% to 0,20 wt %. The parameters were determined from standard methods. ASTM D7896 for thermal conductivity (λ); ISO 3104 for kinematic viscosity (η), and ASTM D92 for flash point and fire point. The experimental results obtained show that the concentration with the best thermal conductivity between 40°C and 65°C is the 0,20 wt% representing sample 3 (E3). There is an improvement of 20,5% compared to the value of the base esters. On the other hand, between 80°C and 90°C, sample E1 of the concentration that constitutes the basic esters (KPOME) presents better results. A decrease of 49.5% compared to the value of the thermal conductivity of the KPOME is noted. The kinematic viscosity decreased with increasing temperature for all samples. Moreover, in the presence of iron oxide 3, this viscosity improves. The most significant improvement is obtained at 100°C with the 0,15 wt% concentration and the least significant is at 40°C for the 0,20 wt% concentration. The tests of flash point allow us to observe that there is a deterioration of this parameter in the presence of FeO₃ nanoparticles in the base bio-insulator (KPOME). The most significant deterioration comes from the sample with a concentration of 0,10 wt%. This means a variation from 155°C to 140,85°C; which gives a deterioration rate of 9,15%. However, the addition of iron nanoparticles rather improves the flash point compared to the base esters. The most important percentage improvement is that of the 0,10 wt% concentration which varies from 160°C to 165,97°C. This represents an improvement of 3,75%.

In this paper, a systematic method for determination of total sulfur in coal by ultraviolet fluorescence is established based on a self-developed large capacity combustion framework (LCCF). The simple oxidation-combustion mode is upgraded to the pyrolysis-oxidation-combustion mode with the help of LCCF. Thus, components to be analyzed is pyrolyzed slowly and the whole decomposition process of sample is prolonged, which could improve the consistence of test results. The sampling size to be sent into LCCF is significantly increased, and the representativeness of samples is secured, which promotes the improvement of accuracy of testing results. Detection limits are augmented without additional hardware or software improvements by this way. The test systems equipped with conventional combustion tube (CCT) and self-developed LCCF are established differently to test standard coal samples (SCS) and ordinary coal samples (OCS) with different total sulfur range. Accuracy and precision of the two test systems are tested and the optimal injection quantity of the system with LCCF is determined. The results show that LCCF could support the injection quantity of 1000mg and ensure stable and complete combustion of sample, which is far more than that of CCT. The accuracy and precision of the test results are better than the requirements of the existing conventional analysis standards, which shows the excellent structure of LCCF and good performance. The new analysis system can further expand the application of ultraviolet fluorescence method in field of coal and others.

Ammonia is considered a potential carbon-free alternative to fossil fuels. However, its unfavorable combustion characteristics and propensity to form fuel NO${}_x$ pose a challenge for its use as fuel for internal combustion engines. The high-pressure dual fuel (HPDF) direct-injection of ammonia could offer the potential to reduce ammonia slip and decrease NO${}_x$ formation. The feasibility of this combustion process has not yet been shown experimentally in literature. This work examines the ignition and combustion characteristics of diesel piloted liquid ammonia sprays under engine-relevant conditions in a rapid-compression-expansion-machine (RCEM). By examining heat release rates (HRRs) under a variety of spatial and temporal spray interaction configurations, charge conditions as well as different diesel pilot amounts and injection durations, the fundamental prerequisites for successful combustion of liquid ammonia sprays are revealed. Strong interaction of the two fuels is found necessary to properly ignite ammonia. Misfiring due to deterioration of the pilot mixture formation can be avoided by injecting diesel first. A strong correlation between main ignition delay and burnout rate suggests a significant influence of wall quenching effects. An investigation of less reactive charge conditions suggests poor suitability of the combustion process for low-load engine operation. While reliable ammonia ignition was achieved for diesel pilot amounts as small as 3.2% of the total injected LHV, ignition is increasingly delayed for smaller pilot amounts. For an operating point, which showed favorable ignition behavior and high conversion rates, pilot fuel amount and injection duration are found to have a major influence on the combustion process.