Diesel Surrogate Fuels Research Articles

Evaluation of Auto-Ignition Characteristics of Diesel Surrogate Fuels with the Same Derived Cetane Numbers at Changed Thermodynamic Environments

Evaluation of Auto-Ignition Characteristics of Diesel Surrogate Fuels with the Same Derived Cetane Numbers at Changed Thermodynamic Environments

EXPERIMENTAL AND REGRESSION ANALYSIS OF COMPRESSION IGNITION ENGINE POWERED BY DIESEL SURROGATE FUEL FROM USED LUBRICATING OIL USING MICROWAVE PYROLYSIS

Fossil fuels are depleting rapidly, and the search for alternative fuels has become inevitable. The researchers investigated the usage of surrogate fuels for internal combustion engines due to the high demand for diesel fuel in all sectors. Diesel surrogate fuels (DSFs) from used lubricating oil seem to be a solution for the future. The disposal of used lube oils poses a major environmental issue that affects the entire planet. This study aims to anticipate the exhaust emissions, brake-specific fuel consumption (BSFC), and brake thermal efficiency (BTE) of a compression ignition engine powered by blends. The blends used are B10 (DSF10% + diesel 90%), B20 (DSF20% + diesel 80%), B30 (DSF30% + diesel 70%), and B50 (DSF50% + diesel 50%) of DSF with diesel through microwave-assisted pyrolysis of used lubricating oil as fuel. Experimental findings were applied to predict each condition's performance characteristics. To estimate the performance characteristics, regression analysis was employed using experimental data in Microsoft Excel and Design Expert-12 software. The experimental data were compared to the simulated data. It was observed that fuel obtained from used lubricating oil using microwave-assisted pyrolysis could be used to power diesel engines without making any changes to the existing engines because the chemical characteristics of the diesel surrogate fuel were almost identical to those of diesel. The BTE of a compression ignition engine with DSF was close when compared to diesel up to full loading condition. At 1.924 kW brake power, the DSF30% has a higher efficiency than the other three blends. It was also observed that the rise in brake power also raises BSFC, thereby lowering thermal efficiency.

Understanding the ignition process and flame structure of conventional and oxygenated fuels under engine relevant conditions – An optical study

Renewably generated synthetic fuels such as poly-oxymethylene ethers (OME) have a significant potential to effectively break the soot-NOX trade-off in compression ignition engines by using exhaust gas recirculation (EGR) to maintain low nitrogen oxide (NOX) emissions while maintaining good efficiency and simultaneously contributing to circular carbon economy. However, owing to the fundamental differences in properties of OME when compared to fossil-based diesel fuels, it is critical to fully understand its ignition and combustion phenomenology to take advantage of this fuel to its utmost potential. In this context, this work outlines the results of a systematic experimental study performed in a heavy-duty, single-cylinder, optical engine probing the spatial and temporal progression of fuel decomposition and ignition behavior of OME when compared to n-dodecane, a diesel-fuel surrogate. Thermodynamic analysis and optical diagnostics techniques including simultaneous HCHO-PLIF and OH-PLIF complemented by high-speed OH* chemiluminescence were employed along with parametric sweeps of intake temperature and EGR dilution rates. OME does not exhibit any observable low temperature heat release irrespective of the ambient oxygen concentration. Differences in the observed diffusive flame structure such as longer flame lift-off length, less pronounced combustion recession, faster premixed burn at ignition (“volumetric” ignition), non-sooting behavior suggest that the inherent presence of fuel-bound oxygen in OME can skew the air-fuel ratio (AFR) distribution within the jet thereby reducing the reliance of combustion on mixing and air entrainment. This leads to rapid late-cycle oxidation leading to shorter combustion duration and favorable combustion phasing. Results also suggest that OME exhibits relatively weak negative temperature coefficient (NTC) behavior, however, the OME fuel-decomposition kinetic-pathways produce significant concentration of HCHO, which might be erroneously interpreted as a product of cool-flames.

Development of a practical soot model for diesel surrogate fuels and oxygenated fuels with specific soot precursor tracking and uniform model structure

Soot formation and oxidation involve several complex processes, which are driven by gas-phase chemistry and soot particle dynamics. An effective soot model for diesel surrogate and practical oxygenated fuels is necessary for predicting the soot emissions to meet the emission regulations in engines. To develop a practical and universal soot model for various fuels without tuning any model parameters under wide operating conditions, it is important to reproduce the soot behaviors for different fuels with distinct molecular structures. In this work, a practical soot model was developed to describe the soot behaviors for diesel surrogate fuels comprising large n-alkane, isoalkane, cycloparaffin, and aromatic hydrocarbon, as well as oxygenated fuels including alcohol and ether. The influence of the fuel molecular structures on the soot behaviors was emphasized by utilizing the specific reaction pathways of polycyclic aromatic hydrocarbon (PAH) production and the specific reaction channels of the soot formation including soot nucleation and PAH condensation for different fuels. An efficient method named the moment projection method (MPM) was employed to describe the soot particle dynamics by directly solving the moment transport equations and track the number of soot particles. By coupling a reduced chemical reaction model for describing the fuel oxidation chemistry and PAH formation, it is found that the soot volume fraction and number density are well predicted for iso-octane, n-heptane, toluene, methanol, n-butanol, dimethyl ether, their mixtures, and diesel surrogate in shock tubes and laminar premixed flames without tuning any model parameters. The effects of equivalence ratio, temperature, and fuel type on soot production are analyzed through the rates of soot nucleation, surface growth, PAH condensation, and oxidation. The computational results indicate that the present model can satisfactorily reproduce the soot characteristics of different fuels with distinct soot formation and oxidation processes.

Effects of ammonia on morphological characteristics and nanostructure of soot in the combustion of diesel surrogate fuels

The morphological characteristics and nanostructure of soot particles in pure n-heptane (C7H16) and n-heptane/ammonia co-flow diffusion flames were analyzed and compared using thermophoretic sampling and transmission electron microscopy (TEM) observation combining with quantitative image information extraction methods. The results showed that the overall formation and evolution of soot particles in NH3-doped n-heptane flames along the flame centerline were similar with that without NH3-doping. However, compared to n-heptane flame, the peak average diameter of primary soot particles and the peak gyration radius of soot aggregates in NH3-doped flames were reduced by about 45% and 37%, respectively, which indicated that the growth of both primary soot particles via surface reaction/condensation and soot aggregates via coagulation were significantly decreased. Meanwhile, the fractal dimension of soot aggregates was lower with NH3 addition as the structure of soot aggregates was looser and tended to be more chain-like. After NH3 doping, the peak average fringe length inside soot particles was decreased by 13%, and the inter-fringe spacing and tortuosity of soot were increased by 8% and 3%, respectively. This represented a more disordered microcrystal structure and lower degree of graphitization of soot particles, meaningfully indicating a higher oxidation reactivity.

The ignition characteristics of dual-fuel spray at different ambient methane concentrations under engine-like conditions

In the present study, dual-fuel ignition process of pilot diesel spray injection into a natural gas-air mixture under engine-like conditions is numerically investigated via large-eddy simulation (LES). Methane and n-dodecane are considered as surrogates for natural gas and diesel fuels, respectively. This study aims to provide understandings of kinetic interactions for dual-fuel spray during the ignition process. The effects of ambient methane concentration on the ignition delay times (IDTs), product distributions, and heat release rates (HRRs) during dual-fuel ignition process are emphasized. The results show that methane prolongs the IDT of n-dodecane, especially for the first-stage IDT. Kinetic analyses reveal that the competition for OH between the dehydrogenation reactions of methane (CH4 + OH <=> CH3 + H2O) and n-dodecane (RH + OH <=> R + H2O) results in the increasing first-stage IDT of pilot spray. Moreover, it is found that the retarding effect positively correlates with the methane concentration. For product distributions, it is observed that the transition of CH2O from fuel-lean to fuel-rich regions is inhibited in the first-stage ignition. In the second-stage ignition, the concentration of CO is decreased as the methane concentration increases and the area with high CO concentration is gradually shifted to the downstream of the spray. In addition, HRRs of low-temperature exothermic reactions appear at the radial periphery as well as the head of the spray front; HRRs of high-temperature exothermic reactions are gradually shifted from the head to the center of the spray with the increase of ambient methane concentration. The HRRs of low- and high-temperature reactions are decreased with increasing ambient methane concentration, and the major reactions for heat release at various ambient methane concentrations are different.

Numerical investigation of component coupling effect on soot forming under low temperature condition

The chemical reactions of each component of hydrocarbon fuels at low temperatures become more complex and the interactions become stronger, which is considered to potentially affect the soot formation characteristics. A 0-dimensional simulation was applied to analysis the component coupling effect on polycyclic aromatic hydrocarbon(PAH) forming process for diesel surrogate fuel, n-heptane/cyclohexane/toluene. The results show that, for the single component, the low temperature reaction of cyclohexane could contribute to the PAH formation while n-heptane inhibit it, and toluene is hardly involved in the soot generation at low temperature. Due to the component coupling effect of multi-component diesel surrogate fuels, the soot generation is significantly reduced at low temperatures, and the pyrene(A4) generation is reduced by 3 orders of magnitude compared to individual components weighted fuels. The generation of O radicals from n-heptane rapidly consumes C6H5O, which replaces its original reaction road to naphthalene(A2). As a result, the reaction time of A2 is shortened by 2 orders of magnitude, then, the generation of A4 and soot are reduced due to the reduction of A2. Therefore, the competition and consumption between the low temperature reaction products and the core radicals of soot generation are the key to reducing soot accumulation.

Effect of Toluene Content on Soot Particle Morphology and Evolution in Coflow Diffusion Flames of Diesel Surrogate Fuels

ABSTRACT Toluene is a representative of aromatics in diesel surrogate fuels, and its influence mechanism on the formation and evolution of soot particles has attracted much attention. In this work, the evolution of the microscopic morphology of soot particles in n-heptane laminar diffusion flame doped with toluene of 0% to 30% was investigated experimentally, and the effects of toluene ratio on particle dynamics such as inception, surface growth and oxidation were analyzed numerically. The experimental results showed that as the toluene ratio increases, the primary particle size increases, and the aggregates first grows from short chains to long chains, then develops to multi-branched chains, which results in Df first decreasing and then increasing, reaching the minimum at 10% toluene. The numerical results showed that the peak inception rate increases linearly with the increase of toluene ratio. The peak rate of HACA surface growth increases slightly due to the increase of particles that could provide active sites and reaches the maximum at ratio of 10% toluene, then decreases slightly due to the limited production of H and C2H2. On the other hand, the PAHs condensation rate increases monotonously, which makes the aggregates more likely to form a loose multi-branched chain structure, and in the subsequent oxidation process, the weak points of the connections between the particles are more likely to be oxidized, resulting in the fracture and fragmentation of the aggregates. For particles oxidation, toluene blending has an opposite effect on soot oxidation by O2 and OH. As the toluene ratio increases, the O2 oxidation rate increases gradually due to the increase of soot volume fraction, while the OH oxidation rate decreases due to the inhibited production of OH. However, the total oxidation rate of particles increases with the increase of toluene ratio.

Development of a Diesel Surrogate Fuel Focusing on the Soot Emission Under Engine Conditions

Development of a Diesel Surrogate Fuel Focusing on the Soot Emission Under Engine Conditions

Development of a Practical Soot Model for Diesel Surrogate Fuels and Oxygenated Fuels with Specific Soot Precursor Tracking and Uniform Model Structure

Development of a Practical Soot Model for Diesel Surrogate Fuels and Oxygenated Fuels with Specific Soot Precursor Tracking and Uniform Model Structure

Development of a Practical Soot Model for Diesel Surrogate Fuels and Oxygenated Fuels with Specific Soot Precursor Tracking and Uniform Model Structure

Development of a Practical Soot Model for Diesel Surrogate Fuels and Oxygenated Fuels with Specific Soot Precursor Tracking and Uniform Model Structure

Analysis of the combustion mechanism of diesel surrogate fuel under CO2/O2 atmosphere

Closed-cycle diesel engine (CCDE) can effectively control CO2 emissions and reduce the greenhouse gas effect, but diesel fuel combustion under an atmosphere with CO2 has the problem of misfire and unclear mechanism. In order to study the CO2 impact on diesel combustion under the CO2/O2 atmosphere, a quantum chemical (QC) model of diesel surrogate fuel (DSF) is proposed, which takes into account the CO2 pyrolysis effect (CO2⇆CO+12O2) and the new reaction of OH radical generation from pyrolysis products (CO+O2+H∙→CO2+OH∙). Firstly, the active sites of the DSF molecules are predicted by average local ionization energy (ALIE) and electrostatic potential (ESP). New chemical reaction paths are obtained using ab initio theory and density functional theory combined with thermodynamic combination algorithm. The QC model is then established by sensitivity analysis and simplification of the mechanism and computational fluid dynamics (CFD) simulation of constant volume combustion chamber (CVCC.) Secondly, the CVCC experiment bench and visualization system are set up. The flame propagation at different times (1.5 ms, 1.9 ms, 2.3 ms, 2.7 ms, 3.1 ms and 3.5 ms) are captured by high-speed cameras under four different CO2 concentrations (air condition, 50%CO2 + 50%O2, 43%CO2 + 57%O2 and 35%CO2 + 65%O2). Finally, the comparison between experiment and model shows that the QC model is suitable for studying combustion characteristics of diesel fuel under CO2/O2 atmosphere. Under maximum CO2 concentration (50%CO2 + 50%O2), The maximum errors of flame combustion limit length (FCLL) and Flame longitudinal section area (FLSA) are 8.54% and 4.94%, respectively. In addition, the CO2 pyrolysis reaction and the new reaction of generating OH radicals indicate that the CO2 chemical effect can promote the combustion of diesel fuel under CO2/O2 atmosphere.

Modeling spray combustion using multi-component surrogate fuels

Kerosene and diesel fuels involved in spray combustion operations are complex fuels composed of a wide and diverse variety of hydrocarbon components. For practical numerical modeling of the evaporation and combustion phenomena in a combustor, well-designed surrogates fuels that can mimic the real fuel thermal and chemical properties can be utilized. In this study, predictions and validations of the influence of fuel on the liquid and vapor penetration characteristics within a constant-volume chamber were first performed utilizing a benchmark m-xylene/ n-dodecane, Jet-A, and diesel surrogate fuels. Then, simulations of reacting spray of a bi-component m-xylene/ n-dodecane fule, and a four-component Jet-A surrogate fuel ( n-dodecane (C12H26), iso-cetane (C16H34), trans-decalin (C10H18) and toluene (C7H8)) were studied aided by skeleton chemical kinetic mechanisms available from the literature. The results of ignition delay time, lift-off length, radicals, and the mass fraction histories of fuel species were comprehensively used to assess the performance of relevant thermophysical and chemical sub-models. Two different chemical mechanisms were compared in detail to investigate the effect of the chemical kinetics model on the flame structures and spray characteristics. It has been found that the spray ignition of multi-component fuels is remarkably influenced by the chosen chemical kinetic mechanism and less affected by the droplet evaporation models.

Influence of pilot-fuel mixing on the spatio-temporal progression of two-stage autoignition of diesel-sprays in low-reactivity ambient fuel-air mixture

The spatial and temporal locations of autoignition for direct-injection compression-ignition engines depend on fuel chemistry, temperature, pressure, and mixing trajectories in the fuel jets. Dual-fuel systems can provide insight into both fuel-chemistry and physical effects by varying fuel reactivities and engine operating conditions. In this context, the spatial and temporal progression of two-stage autoignition of a diesel-fuel surrogate, n-heptane, in a lean-premixed charge of synthetic natural-gas (NG) and air is imaged in an optically accessible heavy-duty diesel engine. The lean-premixed charge of NG is prepared by fumigation upstream of the engine intake manifold. Optical diagnostics include high-speed (15kfps) cool-flame chemiluminescence-imaging as an indicator of low-temperature heat-release (LTHR) and OH* chemiluminescence-imaging as an indicator high-temperature heat-release (HTHR). NG prolongs the ignition delay of the pilot fuel and increases the combustion duration. Zero-dimensional chemical-kinetics simulations provide further understanding by replicating a Lagrangian perspective for mixtures evolving along streamlines originating either at the fuel nozzle or in the ambient gas, for which the pilot-fuel concentration is either decreasing or increasing, respectively. The zero-dimensional simulations predict that LTHR initiates most likely on the air streamlines before transitioning to HTHR, either on fuel-streamlines or on air-streamlines in regions of near-constant ϕ. Due to the relatively short pilot-fuel injection-durations, the transient increase in entrainment near the end of injection (entrainment wave) is important for quickly creating auto-ignitable mixtures. To achieve desired combustion characteristics, e.g., multiple ignition-kernels and favorable combustion phasing and location (e.g., for reducing wall heat-transfer or optimizing charge stratification), adjusting injection parameters could tailor mixing trajectories to offset changes in fuel ignition chemistry.

Deactivation of Ni-Al-Based Catalysts for Autothermal Reforming of Diesel Surrogate Fuel in the Presence of an Aromatic Hydrocarbon.

Diesel fuel can produce higher concentrations of H₂ and CO gases than other types of hydrocarbon fuels via a reforming reaction for solid oxide fuel cells (SOFCs). However, in addition to sulfur compounds and aromatic hydrocarbons in diesel fuel are a major cause of catalyst deactivation. To elucidate the phenomenon of catalyst deactivation in the presence of an aromatic hydrocarbon, dodecane (C12H26) and hexadecane (C16H34) were blended with an aromatic hydrocarbon such as 1-methylnaphthalene (C11H10) to obtain a diesel surrogate fuel. The experiments were performed for autothermal reforming of the diesel surrogate fuel under conditions of S/C = 1.17, O₂/C = 0.24, 750°C and GHSV= 12,000 h-1. Three Ni-Al-based catalysts with 10 wt% (N10A), 30 wt% (N30A) and 50 wt% (N50A) of NiO were prepared via the polymer modified incipient method. Whereas all of the Ni-Al-based catalysts were deactivated with increasing reaction time, the catalysts with greater Ni contents tended to maintain their catalytic performance for a longer time. Correlation between the catalytic performances and Ni content were analyzed by temperature-programmed reduction (TPR), Fourier transform infrared (FT-IR) spectroscopy, scanning electron microscope with energy-dispersive X-ray spectroscopy (SEM-EDX), Brunauer-Emmett-Teller(BET) analysis, X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). Also, we concluded that ethylene (C₂H₄), which was detected by gas chromatography-mass spectrometry (GC-MS), was the fundamental cause of deactivation of the Ni-Al-based catalysts by accelerating the deposition of wire-type carbon on the catalytic surface.

Compositional Effects on Sooting Tendencies of Diesel Surrogate Fuels with Four Components

Systematic investigations of the effects of fuel compositions on sooting tendencies were performed in co-flow methane/air diffusion flames doped with different surrogate blends. Test surrogate fuel...

디젤 모사 연료 구성 성분에 따른 분무 특성 연구

디젤 모사 연료 구성 성분에 따른 분무 특성 연구

Formulating of model-based surrogates of jet fuel and diesel fuel by an intelligent methodology with uncertainties analysis

In this study, an intelligent model to formulate fuel surrogates was proposed which includes intelligent surrogate blend optimizer and optimization module of chemistry kinetic mechanism. The components of surrogates were selected from the library of candidates with given compositions by the intelligent surrogate blend optimizer based on the targeted fuel properties. Hence, new jet fuel surrogate (JFS) and diesel fuel surrogate (DFS) models were formulated consisting of five components (n-dodecane/iso-octane/isocetane/decalin/toluene), with specified compositions of each component, respectively. The new surrogates contain major components of the target practical fuels and inherently emulate the key properties including liquid density, viscosity, surface tension, cetane number, hydrogen-carbon ratio, molecular weight, lower heating value and threshold sooting index. Moreover, a robust skeletal oxidation mechanism of fuel surrogate composed of five components was updated and multi-objective optimization algorithm of non-dominated sorting genetic algorithm II (NSGA-II) was introduced to achieve self-adaptive tuning of Arrhenius pre-exponential factor in fuel-related sub-mechanism. Thus, the optimal rate constants could satisfy the predictions of ignition delay times and species concentrations simultaneously. Then Generalized Polynomial Chaos (gPC) was employed to minimize the uncertainty of stochastic input coefficients and its propagation towards ignition behaviours. Consequently, the new surrogate models were well validated against available tested data from practical fuels, and better performance of current JFS model was highlighted when compared with the prediction results by previous model. It is feasible to employ this intelligent model to formulating surrogates for more practical fuels.

Development of a practical reaction model of polycyclic aromatic hydrocarbon (PAH) formation and oxidation for diesel surrogate fuel

A practical reaction model for the formation and oxidation of polycyclic aromatic hydrocarbons (PAHs) up to coronene (A7) was developed focusing on two diesel surrogate fuels, i.e., a single-component surrogate including n-heptane and a multi-component surrogate including iso-octane, n-decane, methylcyclohexane, and toluene, for engine simulations. The important PAH relevant reactions are identified by using the global sensitivity analysis of the up-to-date detailed mechanisms. In the reduced PAH reaction model, the up-to-date reaction channels involving PAH formation were considered, and the variations and characteristics of the formation pathways of benzene and large PAHs for large alkanes, aromatics, and cycloalkanes with the fuel molecular structure were captured with the present under wide operating conditions. By integrating the PAH reaction model with a reduced oxidation mechanism of the two diesel surrogates, the final chemical mechanism of diesel oxidation consists of 137 species and 447 reactions. The chemical mechanism was extensively validated against the fundamental experimental data including ignition delay times in shock tubes and species profiles in premixed laminar flames, diffusion flames, and jet-stirred reactors (JSR). The performance of the mechanism for the predictions of PAHs from the oxidation of individual component, their mixtures, and diesel fuel was comprehensively evaluated. The computational results indicate that the effect of fuel structure on the PAH formation is satisfactorily reproduced by the present mechanism. Based on pathway analysis in the premixed flame, the contribution of the components in the diesel surrogate for the PAH formation behavior is understood.

An experimental and modeling study of n-hexadecane autoignition under low-to-intermediate temperatures

N-hexadecane is a potential candidate of diesel surrogate fuels and is also the largest linear alkane (n-alkanes) with known chemical kinetic models. The objective of this study is to investigate the autoignition characteristics of n-hexadecane in the low-to-intermediate temperature region and to validate the existing kinetic models. In this study, the ignition delay times (IDTs) of n-hexadecane were measured using a heated rapid compression machine (RCM) at two pressures of 7 and 10 bar, and over equivalence ratios ranging from 0.5 to 1.3. Two-stage ignition characteristic and the negative temperature coefficient (NTC) behavior of total ignition delay time were experimentally captured. This study paid special attention to the influence of pressure, equivalence ratio, and oxygen content on the IDTs of n-hexadecane. It is observed that both the total IDTs and the first-stage IDTs decrease with the rise of those parameters. It is worth noting that the first-stage IDT is found to show a greater dependence on temperature but a weaker dependence on other parameters compared to the total IDT. The observed IDT dependence in the low-temperature region (LTR) were quantitatively described by ignition delay time correlations. The newly measured IDTs were then validated against two kinetic models (LLNL and CRECK). Simulation results show that both models underpredict the first-stage IDT but generally capture the temperature dependence. The CRECK model well predicts the total IDTs of n-hexadecane while the LLNL model significantly underpredicts the total IDTs at most investigated conditions. To the best of our knowledge, this study is the first investigation on n-hexadecane autoignition under low-to-intermediate temperatures, which deepens the understanding of large n-alkane oxidation and contributes to the improvement of the existing kinetic models.