Pure N-heptane Research Articles

Study on laminar combustion characteristics and the optimization of the coupling mechanism in a mixture of propanol and gasoline

When both isopropanol and n-propanol are incorporated, the utilization of propanol as a fuel substitute (or a gasoline additive) presents promising potential for enhancing the combustion efficiency and thermal performance in compact, turbocharged, direct-injection gasoline engines upon blending. However, the complexity of the laminar combustion behavior of propanol-blended gasoline has yet to be fully investigated, as current coupling mechanisms are insufficiently sophisticated to precisely mirror the complex experimental conditions.This study establishes a testbed specifically designed for measuring laminar burning velocity (LBV) using the heat flux method. This setup is employed to measure the LBV of pure n-heptane and isooctane, as well as the LBV of the gasoline surrogate fuel TRF with two distinct blend ratios. Additionally, it measures the LBV of propanol and its blends with TRF. The research findings reveal that isooctane demonstrates a heightened sensitivity to fuel preheating temperature, whereas the toluene proportion in TRF fuels exerts the most pronounced influence on combustion behavior. At an equivalence ratio of 1.1, the LBV of n-propanol differs from that of its isomer, isopropanol, by 4.65 cm/s. Notably, the LBV exhibits a discernible upward trend, corresponding to the increasing proportion of toluene in the blended fuel. Furthermore, there is a pronounced distinction in LBV among the propanol isomers, with blended TRF occupying an intermediate position between pure propanol and TRF. After the enhancement of the mechanism based on experimental benchmarks of LBV, a rigorous validation process demonstrated a substantial improvement in the alignment between simulated outcomes and empirical LBV measurements.

Direct numerical simulation of ammonia/n-heptane dual-fuel combustion under high pressure conditions

Ammonia (NH3) combustion has received increasing attention for its carbon-free nature. However, the utilization of ammonia in engines is constrained by its relatively low reactivity. To overcome this shortcoming, ammonia blending with high-reactivity fuels has been used. In the present work, direct numerical simulation (DNS) of ammonia/n-heptane dual-fuel combustion was performed to understand the effects of ammonia addition on the combustion behavior of n-heptane sprays. Three DNS cases with NH3 energy ratios of 0%, 20%, and 40% were considered. Two-stage combustion was observed in all cases. It was found that both the first-stage and second-stage ignition delay times increase with increasing NH3 energy ratio, and the peak of mean heat release rate (HRR) reduces with increasing NH3 energy ratio. For low-temperature combustion, ignition kernels were observed in the case with pure n-heptane while ignition occurs almost volumetrically in the cases with NH3 addition. The reaction zone of the cases with NH3 addition is thicker compared to that of the case with pure n-heptane. The reactions of NH3 involve radicals, such as OH, which affects the low-temperature combustion of n-heptane. In the stage of high-temperature combustion, individual ignition kernels with significant heat release rate were observed in the cases with NH3 addition, where the reaction zones are thin. In contrast, for the case with pure n-heptane, large heat release rate occurs simultaneously over the entire domain with thick reaction zones. Ignition occurs in regions characterized by low scalar dissipation rate for both low-temperature and high-temperature combustion in all cases. It was found that, though the contributions of NH3-related reactions to the total HRR are noticeable, the contributions of important elementary reactions to the total HRR in pure n-heptane combustion still prevail in the cases with NH3 addition, which indicates that n-heptane chemistry dominates that of NH3 in this work.

Development and evaluation of a skeletal mechanism for EHN additized gasoline mixtures in large Eddy simulations of HCCI combustion

Advanced Low Temperature Combustion modes, such as the Sandia proposed Additive-Mixing Fuel Injection (AMFI), can unlock significant potential to boost fuel conversion efficiency and ultimately improve the energy conversion of internal combustion engines. This is a novel improved combustion process that is enabled by supplying small (<5%) variable amounts of autoignition improver to the fuel to enhance the engine operation and control. Common, diesel-fuel ignition-quality enhancing additive, 2-ethylexyl nitrate (EHN), is doped into gasoline to enable Sandia LTGC + AMFI combustion. This manuscript focuses on the development of a reduced sub-mechanism for EHN chemical kinetics at engine relevant conditions that is implemented into a skeletal mechanism for chemical kinetic studies of gasoline surrogate fuels. The mechanism validation utilized zero-dimensional numerical simulations and comparison to shock tube ignition-delay data of pure and EHN-doped n-heptane. Additional validation is presented with Homogeneous Charge Compression-Ignition (HCCI) engine data of pure and EHN-doped research-grade E10 gasoline. Then, the mechanism was deployed in a 3-D computational fluid dynamics (CFD) using Large Eddy Simulations (LES) to model the HCCI engine experiments of 0.4% vol EHN additized E10 gasoline at several equivalence ratios. Simulations showed a very good performance of the mechanism, and the model accurately reproduced (a) the ignition point, (b) combustion phasing, (c) combustion duration, and (d) the peak of the heat release rates of the engine experiments. The results show that EHN promotes Low-Temperature Heat Release, ultimately driving the gasoline to autoignite at thermodynamic conditions where the fuel would not otherwise ignite. Overall, this work demonstrates a viable reduced chemical-kinetic mechanism for EHN and shows that it can be combined with a skeletal gasoline mechanism for CFD-LES analysis of well-mixed LTGC that matches well with experimental results. The CFD-LES analysis also shows the spatial distribution of EHN-fuel interactions that control the autoignition throughout the combustion chamber.

Effect of ventilation on carbon monoxide and soot particles emissions in a confined and mechanically-ventilated fire

Fire behavior in a 1 m3 confined and mechanically ventilated compartment is investigated experimentally. The main objective is to study carbon monoxide and soot particle emissions by four different fuels: pure n-heptane, technical-grade dodecane, kerosene Jet A-1, and Mobil DTE oil heavy medium. Air Renewal rates are set at 4.83 ACH, 9.67 ACH, and 17.8 ACH, while the fuel pan diameters are 0.115 m, 0.14 m, and 0.19 m. The results show that decreasing the renewal rate or increasing the pan size decreases the mass loss rate and soot emissions. However, CO emissions increase. Lighter fuels exhibit higher mass loss rates and CO emissions than heavier fuels. The highest smoke temperatures are produced at high renewal rates and large pan diameters. Meanwhile, soot emission levels decrease in the order of kerosene > dodecane > Mobil oil > heptane. High levels of soot but low CO emissions are present in well-ventilated fires. However, high CO but low soot emissions appear in under-ventilated fires. The soot particles collected in the smoke layer show unimodal distribution. The modal diameter of the particles ranges from 220 nm to 300 nm.

Oxidation of Methane/n-Heptane Mixtures in a High-Pressure Flow Reactor

To evaluate the use of diesel as a pilot fuel in natural gas combustion in two-stroke maritime engines, research on high-pressure oxidation of methane/n-heptane mixtures is of interest. In this study, laminar flow reactor experiments were conducted at pressures of 21 and 100 bar, temperatures in the range 450–900 K, and under stoichiometric and fuel-lean conditions. For all conditions, the n-heptane conversion starts below 600 K. A pronounced negative temperature coefficient region was observed at 21 bar. The n-heptane was depleted at all conditions before reaching 900 K. Methane oxidation was initiated once n-heptane was consumed. Compared to the oxidation of pure n-heptane and NH3/n-heptane mixtures, the presence of methane promoted n-heptane oxidation in the full temperature range. The model from Zhang et al. provided overall a good agreement with the experimental data. However, the low-temperature conversion of n-heptane at 21 bar and stoichiometric conditions is underpredicted, possibly because some chemical coupling between n-heptane and methane is missing in the model.

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.

A new skeletal kinetic model for methanol/ n-heptane dual fuels under engine-like conditions

In dual-fuel engines, diesel is typically used to initiate the ignition of methanol, resulting in a turbulent spray flame. However, the lack of skeletal or reduced mechanisms for methanol/n-heptane blends limits the further research of dual-fuel combustion. Therefore, a skeletal methanol/n-heptane mechanism including 52 species and 182 reactions was proposed based on the decoupling method. Firstly, it was validated by the recent experiments for blends and compared with several mechanisms. Good agreement between the predicted and measured results was obtained in terms of the ignition delay time, laminar flame speed, and species distributions for pure n-heptane and methanol as well as blends. The new mechanism shows improvements on the negative temperature coefficient (NTC) behavior and the low-temperature ignition for blends compared with other mechanisms. Secondly, the effect of methanol on n-heptane decomposition was investigated based on kinetic analysis. Results showed that methanol competes OH with n-heptane at low temperatures, mainly prolonging the second-stage ignition process. At high temperatures, more HO2 was produced via CH3OH→CH2OH→CH2O + HO2. The existence of methanol also removes the NTC regime toward lower temperatures at intermediate temperatures. Methanol/n-heptane dual fuels no longer exhibit NTC behaviors with high concentration methanol.

Reaction zone characteristics of iso-pentanol swirl spray flames using OH-PLIF and 2C-LII

This paper focuses on the reaction zone and soot emission characteristics of swirl spray flames of iso-pentanol and blends. OH planar laser induced fluorescence (PLIF) measurements were used to study the lift-off and local extinction features. Soot emission was investigated using the planar time-resolved two-colour laser induced incandescence (2C-LII) diagnostic technique. Fuels used in this study were n-heptane, iso-pentanol, ethanol and blends of n-heptane/iso-pentanol and n-heptane/ethanol. Different operating conditions were tested and categorized into three flame types including stable, near blow-off, and far away from blow-off. A clear double flame sheet structure appeared in most flames, referred to as the inner and outer regions in this study. Also, all flames other than pure iso-pentanol displayed an open-up spray in a cone-like “V” shape. Results of stable and near blow-off conditions showed that the addition of iso-pentanol to an n-heptane flame caused the flame to become more attached to the bluff-body. In stable flames, the addition of iso-pentanol to n-heptane increased the occurrence of local extinctions. Whereas the addition of ethanol to n-heptane decreased occurrences of local extinction. Across near blow-off conditions, the impact on lift-off height caused by the addition of ethanol to n-heptane was less than that of the addition of iso-pentanol to n-heptane. In the far from blow-off conditions, less local extinction in pure iso-pentanol was found compared to the n-heptane/iso-pentanol mixture. Soot volume fraction of the iso-pentanol flame was less than the n-heptane flame, and the addition of iso-pentanol to the n-heptane flame reduced the soot volume fractions to a lower level than in the pure n-heptane flame.

ESIPT in a binary mixture of non-polar and protic polar solvents: Role of solvation dynamics

Excited-state intramolecular proton transfer (ESIPT) was studied for two different fluorophores M2N3HF and 2P3HBQ in binary solvent mixtures of n-heptane and methanol. While both fluorophores share a degree of structural resemblance, they exhibit sharply contrasting ESIPT dynamics in the solvent mixtures. For 2P3HBQ, ESIPT is ultra-fast in n-heptane, followed by monotonic retardation in the solvent mixtures as the proportion of methanol increases, due to the predominance of 2P3HBQ⋯Methanol intermolecular H-bonding over intramolecular H-bonding within the 2P3HBQ molecule, at high methanol concentrations. For M2N3HF on the other hand, ESIPT is known to occur within sub-picosecond time-scales in alkanes and within few tens of picoseconds in methanol. However, addition of minor quantities of methanol into an alkane solvent like n-heptane causes the ESIPT to be dramatically arrested: even at 3 % mole fraction of methanol, it requires several 100 ps to complete, thus becoming ∼ 1000-fold slower than that in pure n-heptane, and ∼ 5-fold slower than that in pure methanol. Our results demonstrate that the ESIPT time-constants of M2N3HF in the solvent mixtures follow the same trend as solvation time-constants, suggesting that solvent relaxation plays a major role in the re-distribution of intra- and intermolecular H-bonds in the excited state M2N3HF. Unlike 2P3HBQ, the ESIPT of M2N3HF is thus coupled to the solvation dynamics of the solvent medium.

Primary atomization of liquid-fuel jets in confined turbulent pipe-flows of air at elevated temperatures

The primary atomization of evaporating laminar liquid jets of either pure n-pentane or n-heptane injected continuously from a circular nozzle concentrically and axisymmetrically into high-temperature turbulent coflows of air in confined a pipe has been studied experimentally. Fuel-jet bulk velocities up to 2.7 m/s, air coflow bulk velocities up to 37 m/s and temperatures up to 1150 K were investigated within a 25 mm round pipe. In the near-field region of the injector nozzle, liquid fuel jets were formed whose length increased with the fuel injection velocity and decreased with the air velocity. Smaller droplets were formed at both higher fuel and air velocities. Droplet diameters within the range from 200 to 900 µm were measured, indicating the polydispersed nature of the fuel spray. The mean droplet diameter increased non-monotonically with increasing axial distance from the nozzle due to a complex competition between droplet coalescence and evaporation. No significant effect of the air inlet temperature was observed within the investigated range of conditions on the jet length and droplet size. However, smaller droplets were obtained in flows with lower turbulence intensities and longer longitudinal integral lengthscales. Analysis of the data reveals that the mean droplet diameters can be predicted by the empirical expression (dmean/djet) = 34 × 103 We∆1.29Re∆-3, independent of the two perforated plates selected and used in the present work. The resulting data can contribute towards a better understanding of interfacial dynamics, and the development and validation of advanced multiphase-flow and reacting-flow models.

Investigation of Aggregation Behavior and Molecular Weight Changes of Asphaltene Model Compound

We investigate the aggregation of Violanthrone-78 (VO-78), a model asphaltene compound, in mixtures of toluene and n-heptane (heptol) using spectroscopic and dynamic and static light scattering techniques. The light scattering experiments were conducted using pure toluene and n-heptane, as well as 25/75, 50/50, and 75/25 heptol solvents. Furthermore, the concentration of VO-78 varied from 10-8 M to 10-3 M in these suspensions. The dynamic light scattering experiments were used to study the aggregate sizes from the intensity autocorrelation function at different n-heptane volume fractions. The results show the onset of aggregation of about 50 % n-heptane volume fractions. The aggregate sizes in toluene, within the range of concentrations examined, were below the instrument's detection limit (< 5 nm) but increased with increasing dosages of n-heptane. On the other hand, the aggregate size in pure heptane was observed to be greater than the maximum limit of the instrument (> 10 μm). Furthermore, the static light scattering experiments provided an anomalous behavior. Increasing concentrations of VO-78 in the solvent resulted in lowering the parameter Kc/Rq, where c is the molar concentration.

Soot formation in n-heptane/air laminar diffusion flames: Effect of toluene addition

The mixture of n-heptane and toluene is regarded as surrogate fuel for diesel. Under the premise of a certain carbon flow rate, the particle size, nanostructure, microcrystalline size and soot deposition morphology of three kinds of fuel laminar diffusion flames were studied by Transmission Electron Microscopy (TEM), High Resolution Transmission Electron Microscopy (HRTEM), X-ray diffractometer (XRD) and Field Emission Scanning Electron Microscopy (FESEM). The three fuels were pure n-heptane (T0), toluene / n-heptane blends with 5 vol% (T5) and 10 vol% (T10) toluene, respectively. Thermophoretic probe sampling and SiC fiber deposition were used to obtain soot samples. The results showed that with the increase of toluene content, the flame height increased and the temperature decreased at the same height. The addition of toluene increased the content of PAHs, which promoted the formation of soot, and increased the number and particle size of soot. At HAB = 30 mm, with the increase of toluene content, the graphitization degree of soot increased, which showed a larger soot fringe length and a smaller fringe tortuosity, and microcrystalline width (La) of soot particles increased gradually. It is worth noting that the size of a new structure in the soot deposition is counted for the first time, and it is found that its size is negatively correlated with the fringe length and microcrystalline width of soot.

Size distribution of primary submicron particles and larger aggregates in solvent-induced asphaltene precipitation in a model oil system

Asphaltene precipitation is a crucial phase separation phenomenon in the oil industry, especially in paraffinic froth treatment to extract bitumen from oil sands ores. This work reveals the ubiquitous presence of particles at 0.2 to 0.4 μm in radius, defined as primary sub-micron particles (PSMPs) at early stage asphaltene precipitation from diffusive mixing with solvents. We observed PSMPs in a quasi-2D chamber where asphaltene solution (the model oil) is displaced by 3 paraffinic solvents, the blends of solvents, and solvents containing inhibitor at low concentrations. The yield and size distribution of asphaltene particles are affected not only by the Hildebrand solubility parameter of the precipitants but also by the diffusion coefficients of the asphaltene solution and the precipitant. Even though n-pentane is a stronger solvent than n-heptane, the yield of asphaltene in the diffusive mixing chamber is close because of the difference in the diffusion coefficient between n-pentane and n-heptane in asphaltene solution. The results of n-heptane and n-decane blends reveal that the increase of the ratio of PSMPs compared with pure n-heptane or n-decane. The inhibitors significantly decrease the aggregation rate of PSMPs, displayed as a higher ratio of PSMPs compared to a non-inhibitor group. The population balance model (PBM) with the Hildebrand solubility parameter has been used to model particle size distribution. Good agreement has been achieved between numerical predictions and the experimental data. It indicates that the colloid theory can describe the size distribution of PSMPs and larger aggregates in early stage of asphaltene precipitation. This study illustrates the importance of mixing dynamics on the size distribution in asphaltene precipitation. The findings can be useful for accurate modeling of the hydrocarbon separation or asphaltene precipitation.

Liquid-Vapor Interfacial Tension in Alkane Mixtures: Improving Predictive Capabilities of Molecular Dynamics Simulations.

The liquid-vapor interfacial properties of hydrocarbons and their mixtures are important factors in a wide range of industrial processes and applications. Determining these properties experimentally, however, is not only practically demanding, but many important properties, such as phase densities and compositions are not directly experimentally accessible, thus requiring the development of theoretical models. Molecular dynamics (MD) simulations, by contrast, are relatively straightforward even for the most complex of mixtures and directly provide all of the microscopic quantities for the studied systems. We have previously applied MD simulations to study the liquid-vapor equilibria of mixtures of hydrocarbons and CO2 that are particularly relevant to hydrocarbon recovery from geologic formations. In this study, we explore in more detail the robustness of the simulation methods with respect to the choice of the model system parameters, investigate the accuracy of the simulations in determining the key quantities: system pressure and interfacial tension (IFT), and, finally, devise a simple correction for achieving a much closer agreement between the simulated and experimental quantities. We perform extensive MD simulations for three mixtures, propane/n-pentane, propane/n-hexane, and CO2/n-pentane, using model systems from 1000 up to 100 000 molecules, and different simulation box dimensions to test for the sensitivity to finite-size effects. The results show that changing the system size and box dimensions does not significantly impact the accuracy of the simulations. Subsequently, we examine the accuracy of the MD simulations in determining the pressure and IFT for two pure hydrocarbon systems, n-pentane and n-heptane. Finally, we propose a simple linear correction formula for the pressures and IFTs obtained from the MD simulations that closely reproduce the experimental values for single components and mixtures of hydrocarbons. Our results enable the MD simulations to provide more accurate and reliable predictions of the interfacial properties, thereby reducing the need for challenging laboratory experiments.

Ignition and flame stabilisation of primary reference fuel sprays at engine-relevant conditions

This study aims to investigate the underlying processes governing ignition and flame stabilisation in compression-ignition (CI) engine-relevant conditions. The experiments feature a canonical configuration with a single fuel jet injected into a constant-volume combustion chamber. Primary reference fuels (PRFs), including PRF100 (neat iso-octane, a gasoline surrogate), PRF80 (a blend of 80 vol.% iso-octane and 20 vol.% n-heptane) and PRF0 (neat n-heptane, a diesel surrogate), were tested to simulate changes in fuel ignition quality inside a quiescent steady environment with an ambient density of 22.8 kg/m3 and an O2 concentration of 15 vol.%. The ambient gas temperatures were controlled at 1150 K (PRF100), 1120 K (PRF80) and 900 K (PRF0), in order to adapt to the fuel reactivity so that a constant ignition delay of 1.15 ms can be achieved for all blends. This approach was employed in order to substantially reduce the effect of fuel-oxidiser mixing prior to ignition while highlighting the effect of fuel chemistry on the ignition process and flame evolution. Under the test conditions of this study, optical imaging reveals that the blends with higher iso-octane content exhibit a faster spreading of combustion after ignition and establish a steady lifted flame that is closer to the nozzle. Imaging by CH2O-PLIF indicates that blends with higher iso-octane content produce CH2O that is distributed across larger portions of the jet at an earlier timing when compared to neat n-heptane that shows a propagating first-stage ignition through the fuel jet. Supporting unsteady flamelet calculations are presented to investigate the effect of chemistry and turbulent mixing. The flamelet calculations agree qualitatively in several respects to the experiments, especially in the spatial and temporal trends for CH2O production and consumption. Synthesis of the flamelet and experimental results suggests that for the iso-octane-containing fuels, CH2O is formed via single-stage ignition reactions rather than exhibiting the typical two-stage ignition behaviour which is found in the pure n-heptane fuel case. Furthermore, the flamelet calculations suggest high-temperature ignition occurs first in lean mixtures in the iso-octane-containing fuel cases, but in rich mixtures for the PRF0 case. If autoignition is the mode of flame stabilisation, this provides an explanation for why the PRF100 and PRF80 cases stabilise further upstream, since lean mixtures have longer residence times, experience lower scalar dissipation rate, and may be more likely to be exposed to a supporting peripheral reservoir of hot products, should one exist. Overall, this study provides insights into the roles of fuel chemistry and turbulent mixing on the ignition and combustion behaviour of PRFs under engine-relevant conditions.

Vapor-liquid equilibrium and criticality of CO2 and n-heptane in shale organic pores by the Monte Carlo simulation

Thanks to the application of CO2 enhanced oil recovery (EOR) technology in shale oil production, phase behavior of CO2 and alkanes in nanopores has received considerable attention. Understanding the confinement effect on the vapor–liquid equilibrium and critical state of CO2 and alkanes is imperative to the calculation of phase behavior and prediction of oil recovery. In this work, the vapor–liquid equilibrium of pure CO2 and n-heptane (nC7) and their mixtures in shale organic pores are simulated using the Monte Carlo simulation. Compared to the bulk phase, the density of equilibrium gas is larger due to adsorption while the liquid phase density is lower because of capillary condensation. The influence of the confinement effect on the equilibrium phase composition results in the lower bubble point pressure and higher dew point pressure of the binary system. Changes in the equilibrium phase lead to a decrease in the critical temperature and pressure of single-component fluids and the minimum miscible pressure of binary system in nanopores. We fitted the critical property shift and analyzed the influence of pore size on fluid properties such as equilibrium pressure, composition, critical parameters, density distribution, etc. This study provides better insight into vapor–liquid equilibrium and critical state of CO2 and alkane in shale organic pores.

Isobaric heat capacity measurements of natural gas model mixtures (methane + n-heptane) and (propane + n-heptane) by differential scanning calorimetry at temperatures from 313 K to 422 K and pressures up to 31 MPa

Heat capacities of pure methane (1), propane (2) and n-heptane (3), and binary mixtures of (methane or propane + n-heptane) at n-heptane mole fractions of (0.070 to 0.750), were measured at temperatures (313 to 422) K and pressures (6.00 to 31.10) MPa using a Tian-Calvet-type differential scanning calorimeter with a combined standard uncertainty of (2.20 to 2.68) % (k = 1). The results for pure methane, propane and n-heptane agreed within 2% of the values calculated from reference equations of state (EOS). In contrast, for the two sets of mixtures measured above their cricondenbars, averaged absolute deviations of 4.6%, 3.7% and 1.2% were observed between the measured cp values and those predicted by the GERG-2008, Peng-Robinson (PR) and SAFT-γ Mie EOS, respectively. The divergences of cp from model calculations for the binary mixtures near the critical region were also investigated. The root mean square (r.m.s.) deviations of the measured heat capacities from those calculated using the GERG-2008, PR, and SAFT-γ Mie exhibited relatively large but similar values of 7.1%, 7.4% and 7.2% for [0.850 CH4 + 0.150 n-C7H16] and 9.1%, 6.9% and 8.0% for [0.930 C3H8 + 0.070 n-C7H16]. This work reveals that the SAFT-γ Mie EOS can adequately describe most heat capacity data above the cricondenbar, while none of the models provide reliable predictions near the critical region.

Experimental investigation on soot formation characteristics of n-heptane/butanol isomers blends in laminar diffusion flames

Biobutanol is a highly competitive alternative biofuel for fossil fuels in the future. However, there is no consensus on the soot formation of the four butanol isomers. The soot formation characteristics of the pure n-heptane (B00) and the volumetric mixture 50% n-heptane/50% butanol isomer (H50B50) flames were investigated on a coflow burner. The quantitative soot volume fraction, qualitative OH radical concentration, morphological parameters and nanostructures of soot particles were measured by the two-color laser induced incandescence (TC-LII) method, the planar laser induced fluorescence (PLIF) method, and transmission electron microscope (TEM) analysis. Compared with B00 flame, the soot loading of n-heptane/n-butanol (N50), n-heptane/s-butanol (S50) and n-heptane/i-butanol (I50) flames decreased by 62%, 40% and 33%, respectively, whereas the n-heptane/t-butanol (T50) flame increased by 57%. The oxidation of soot particles was jointly affected by the region and the peak concentration of OH radical. As the flame developed, the primary particle diameter initially increased and then decreased in the order T50 > I50 > S50 > N50. Regarding soot nanostructure, the fringe tortuosity and inter-fringe spacing of soot sampled in the three flames decreased in the order I50 > S50 > T50.

Operating range, combustion, performance and emissions of an HCCI engine fueled with naphtha

In this study, it was aimed that the effects of naphtha on homogeneous charged compression ignition (HCCI) combustion, performance, exhaust emissions and operating range were researched experimentally in an HCCI engine. The test engine was able to operate with HCCI mode between 800 and 2000 rpm and λ = 1.61–λ = 2.93 lambda values range at constant inlet air temperature of 60 °C. Pure n-heptane and naphtha, N25, N50 and N75 fuel blends were used as test fuels. Experiments showed that knocking tendency reduced with the increase of lambda. Similarly, more stable combustion was obtained with the addition of naphtha into n-heptane due to higher octane number. Test results showed that HCCI combustion was delayed when naphtha fraction increased in the test fuels. MPRR was obtained as 15.6 bar/°CA and 11.9 bar/°CA with n-heptane and naphtha respectively at λ = 2 and 1000 rpm. ITE increased from 29% to 37% with naphtha according to n-heptane at λ = 2 and 1000 rpm. On the contrary, HC and CO increased from 331 ppm to 411 ppm and 0.051% to 0.075% with naphtha compared to n-heptane at λ = 2 and 1000 rpm, respectively. It was also seen that Naphtha showed wider HCCI operating range according to n-heptane especially knocking zone.

Density, Speed of Sound, Compressibility and Related Excess Properties of Methane + n-Heptane at T = 303.15 K and p = 10 to 70 MPa

Density and speed of sound of methane + n-heptane binary mixtures were measured at a temperature equal to 303.15 K and at pressures ranging from 10 MPa to 70 MPa. The measurements were performed in pure n-heptane and eight different mixtures with methane molar percentage ranging from 20 % to 95 %. Speed of sound data was obtained by a pulse-echo technique working at 3 MHz whereas density data were acquired from a vibrating U-tube densimeter. Isothermal and isentropic compressibilities were derived from both measurements in the same conditions. Finally, partial molar volumes, excess molar volume, excess isothermal compressibility as well as excess speed of sound and excess isentropic compressibility were estimated at the same conditions and the relative excess properties were represented as a function of methane content. From these measurements, it was observed that the large difference in compressibility of pure components provoked significant deviations to ideal behavior with relative excess values that can reach − 20 %, − 100 % and 200 % of the ideal properties for molar volume, isothermal compressibility and speed of sound, respectively. Moreover, a small clustering effect at high dilution of n-heptane at 30 MPa was brought forth to light by evaluating the partial molar volumes.