High Pressure Temperature Conditions Research Articles

Synthesis and characterization of hydrophilic gilsonite fine particles for improving water-based drilling mud properties

In this study, hydrophilic gilsonite fine particles were produced by reaction of natural gilsonite with a mixture of sulfuric acid and nitric acid followed by a planetary ball mill process. The hydrophilic gilsonite was characterized using FTIR, XRD, FE-SEM, DLS, elemental analysis, and mass spectroscopy. All experiments showed that the characteristics of the hydrophilic gilsonite, due to its surface modification, were different from those of natural gilsonite. Moreover, hydrophilic gilsonite molecules were dispersed in water as fine particles with an average diameter of 300 nm without adding any dispersant. The effects of hydrophilic gilsonite on the rheological properties as well as the fluid loss of the water-based drilling mud were investigated before and after the hot-roll process. The results showed that simultaneous adding of 10 g of hydrophilic gilsonite fine particles to the base fluid and reducing the starch concentration to half of its initial value resulted into the best composition for efficient water-based drilling mud. In this case, the rheological properties of the mud were stabilized with a minimum change in the decrease of the yield point, foam formation was prevented after the hot-roll process, and the pH of the system was stabilized in a suitable range at high temperatures. Moreover, this composition could reduce the fluid loss by 50.8% and the filter cake thickness by 66.7% in low-temperature, low-pressure conditions, while the fluid loss reduction was 75% in high-temperature high-pressure conditions. Moreover, the results revealed that hydrophilic gilsonite was an effective additive during the 16 h hot-roll process.

Ionic liquid in stabilizing asphaltenes during miscible CO2 injection in high pressure oil reservoir

The potential of ionic liquids to prevent asphaltene precipitation during miscible Carbon dioxide (CO2) flooding was investigated. Asphaltene dispersion tests were performed to compare the effectiveness of commercial inhibitors and the ionic liquids at ambient conditions. Based on the results 1-Butyl-3-methyl-imidazolium bromide [BMIM][Br], Ionic Liquid was selected and asphaltene onset pressure (AOP) was determined at high-temperature high-pressure conditions through isothermal depressurization experiments in PVT cell. The effect of CO2, organic solvents and [BMIM][Br] on AOP were documented and correlated with nodal pressure analysis of the reservoir/wells.The results show a 21% decrease in AOP compared to the untreated oil and about 46% decrease when 35 mol% of CO2 is solubilized in oil. [BMIM][Br] is seen to have higher activity when injected in solution with isopropanol-n-heptane compared to direct addition. The application of [BMIM][Br]in miscible CO2 flooded reservoir is found to have good potential in inhibiting asphaltene deposition within the reservoir and near wellbore nodal conditions.

Distributed Fiber Optic pH Sensor for the Application in the Wellbore

pH measurement is important in many applications such as environmental science, civil engineering, biotechnology, earth science, and marine sciences. In the wellbore, the pH of the cement pore solution is around 13 at early stage, and the wellbore cement is relatively stable and less permeable above pH 10.5. However, pH drops in the CO2/H2S containing environment making the cement more porous and permeable, which leads to higher risk of wellbore integrity failure. The lower pH also makes the casing steel more susceptible to corrosion. Therefore, real time monitoring of pH in the wellbore is crucial for corrosion detection and cement failure prediction. Wellbores are often at high temperature high pressure (HTHP) conditions (> 149 °C, >1400 psi). Conventionally, pH measurement is made by a glass electrode, which is fragile, prone to drifting, and suffers from alkali interference. Furthermore, it requires a reference electrode, which becomes less stable and less reliable in HTHP conditions, hence there are only limited options available for conventional pH sensors under wellbore conditions. In the contrast, fiber optic pH sensors can offer desirable advantages such as the elimination of electrical connections and wiring and the lack of need for a separate reference electrode, making them inherently more compatible with harsh environment applications. Importantly, they can also be used for remote, distributed, and continuous pH sensing in harsh environment to enable a map of pH throughout a region of interest. Therefore, fiber optic sensors have become a promising solution for pH monitoring in the wellbore. To enable distributed pH sensing with the optical fiber platform, an optical fiber must be integrated with a pH sensitive layer along the fiber, such that the optical properties can be locally altered due to the pH change of the surrounding solution and the change is monitored by a detector in either a transmission or reflection/backscatter configuration. Therefore, the development of a stable, selective, and sensitive pH sensing layer is the critical enabling technology. Sol-gel SiO2 film is one of the most widely used substrates to immobilize pH indicators, such as organic dyes, on the optical fiber surface for pH sensing. SiO2 film has high thermal stability and excellent mechanical strength, which satisfies the HTHP wellbore conditions. The SiO2 thin film can be prepared over a large area at a comparatively low cost. Most investigations use the sol-gel SiO2 film as the substrate for immobilizing pH indicators, but very few studies have reported that the film itself can be used as a pH sensing layer. Using only SiO2 film makes the pH sensor simple to fabricate and free of leaching or photobleaching which are often encountered by the entrapped dye indicators. However, the mechanistic details of the response require elucidation to understand the potential for a selective and sensitive response as a function of pH in the presence of other chemical analytes and variations in temperature and pressure. Here we report recent results on fiber optic pH sensors utilizing porous silica based films and discuss them in the context of fundamental mechanistic considerations as well as their relevance to harsh environment sensing applications. The SiO2 film is coated onto the optical fibers through a sol-gel dip-coating method. The dip-coated fibers are calcined at temperatures of 200-600oC afterwards to obtain a porous SiO2 film of a few hundred nanometers thick. The pH sensing performance is investigated in terms of light transmission to confirm sensitivity and reversibility, and the distributed pH monitoring capability is demonstrated using an optical backscatter reflectometer. The optical fiber coated with a silica-based sol-gel and calcined at 200 °C shows good sensitivity and reversibility in the pH range from 4 to 13, and the sensor is found to be more sensitive in the alkaline region, which indicates that the developed fiber optic pH sensor has potential application in the wellbore pH range.

Application of a novel acrylamide copolymer containing highly hydrophobic comonomer as filtration control and rheology modifier additive in water-based drilling mud

Deep wells suffer from the instability and disintegration of natural polymers and other commonly used additives under high pressure and high temperature condition. As a result, serious problems such as hydraulic loss, stuck pipe, and high torque and drag are expected to take place which leads to a dramatic increase in cost and time. This study presents the functionality of a novel synthetic based acrylamide-styrene copolymer (SBASC) as a supersede additive for water-based drilling mud. First, the SBASC was synthesized using an emulsion polymerization process and its particle morphological and polymer chain structural properties were determined by Field Emission Scanning Electron Microscopy (FESEM) and Fourier- Transform Infrared Spectroscopy (FTIR), respectively. Then, the designated copolymer was added into a mud formulation which is applicable in oil and gas fields, and its performance in the mud was investigated with respect to filtration properties and rheological characteristics. In addition, the rheological characteristics and filtration behavior of drilling fluids containing SBASC were compared with those of a field applicable fluid that contained 9 g of HT starch which is a commercial natural polymer commonly used in drilling fluid industry. Furthermore, the thermal stability of SBASC was determined by conducting hot rolling and high pressure-high temperature (HP-HT) filtration tests. The obtained results confirmed that the addition of the copolymer enhances the rheological characteristics of the drilling fluid before and after aging at 121.1 °C. Moreover, the filtration behavior at both conditions was improved by introducing SBASC into the fluid, while the best performance was observed for the fluid containing 3 g of SBASC which shows 38.8% and 47.5% fluid loss reduction for HP-HT and LP-LT conditions, respectively. Furthermore, the solubility of SBASC in saline and fresh water is verified by demonstrating a promising solubility in high salinity water sample with different concentrations of a monovalent salt.

Failure analysis for the cement with radial cracking in HPHT wells based on stress intensity factors

Wells are often cemented to provide zonal isolation and structural support through their entire service lifetime. Even if a cement sheath is set properly, it may inevitably contain small cracks which tend to propagate under harsh environmental and operational conditions. This work presents a mechanical model to predict the stress intensity factor at a radial crack tip in the cement under high pressure/high temperature (HPHT) conditions. The well section comprised of casing-cement-formation is modeled as three isotropic material domains under plane strain condition. The model calculates the stress field in the well section and estimates the stress intensity factor by a distributed dislocation technique. Two failure factors corresponding to the material strength criterion and fracture propagation criterion are introduced to evaluate the cement integrity. The influence of loading conditions and cement's mechanical and thermal properties on the failure factors is also investigated. The results indicate the predominant failure mode under HPHT conditions. The proposed model provides guidelines for the assessment of cement sheath integrity based on fracture mechanics.

Wettability of calcite under carbon storage conditions

Knowledge of interfacial properties, including both fluid-fluid interfacial tension and mineral wettability is essential for accurate simulation of carbon dioxide storage in geological formations. In this context, carbonate reservoirs, especially saline aquifers, are of great interest due to their vast storage capacities; therefore, it is imperative to attain a thorough understanding of their wettability under the high-pressure, high-temperature (HPHT) conditions of CO2 storage. To this purpose, contact angles have been measured for the system CO2 + NaHCO3(aq) + calcite under HPHT conditions. Calcite is representative of limestone minerals and the brine chemistry and molality (1 mol·kg−1) have been chosen to inhibit dissolution reactions. Both static (sessile drop) and dynamic (tilting plate) contact angle measurements were carried out under reaction-free conditions at temperatures from (298 to 373) K and at pressures up to 30 MPa. The influences of surface roughness and cleanliness have also been addressed in this study. We found that calcite is mainly brine-wet, but it can turn intermediate-wet or even weakly CO2-wet at intermediate pressures (around 10 MPa) and low temperature conditions (around 300 K). The results presented in this work may prove useful for characterizing the wettability of a wide variety of calcite (limestone) surfaces that one might expect to encounter in natural reservoirs.

Improved Filtration Properties of Polystyrene Nanoparticle additives to Water Based Drilling Fluid

This work present polystyrene nanoparticle, a new nanoparticle that is non-conductive and less expensive. Polystyrene nanoparticle added to water based drilling fluid design and tested for filtration loss at Low Pressure Low Temperature (LPLT) condition (25°C and 100 psi) and High Pressure High Temperature (HPHT) condition (150°C and differential pressure of 500 psi). In comparison to based fluid design, polystyrene nanoparticle added drilling fluid reduced filtration loss by 29%. While in comparison to base fluid and polymer drilling fluid, the polystyrene nanoparticle added drilling fluid reduced filtration loss by 50.7% under LPLT condition. Under HPHT condition, polystyrene nanoparticle added drilling fluid reduced fluid loss by 44.4% in comparison to base fluid. While in comparison of base fluid, polymer and polystyrene nanoparticles reduced fluid loss by 61.1%. Polystyrene nanoparticle drilling fluid formed a thin non-erodible low permeability filter cake, this showed that polystyrene nanoparticles plugged the pores of the filter cake. Thus, it can be concluded that polystyrene nanoparticle improved filtration control of water based drilling fluid.

Boron–oxygen complex yields n-type surface layer in semiconducting diamond

Diamond is a wide-bandgap semiconductor possessing exceptional physical and chemical properties with the potential to miniaturize high-power electronics. Whereas boron-doped diamond (BDD) is a well-known p-type semiconductor, fabrication of practical diamond-based electronic devices awaits development of an effective n-type dopant with satisfactory electrical properties. Here we report the synthesis of n-type diamond, containing boron (B) and oxygen (O) complex defects. We obtain high carrier concentration (∼0.778 × 1021 cm-3) several orders of magnitude greater than previously obtained with sulfur or phosphorous, accompanied by high electrical conductivity. In high-pressure high-temperature (HPHT) boron-doped diamond single crystal we formed a boron-rich layer ∼1-1.5 μm thick in the {111} surface containing up to 1.4 atomic % B. We show that under certain HPHT conditions the boron dopants combine with oxygen defects to form B-O complexes that can be tuned by controlling the experimental parameters for diamond crystallization, thus giving rise to n-type conduction. First-principles calculations indicate that B3O and B4O complexes with low formation energies exhibit shallow donor levels, elucidating the mechanism of the n-type semiconducting behavior.

The role of thermal stress in near wellbore instabilities and its implications: a case study from the HTHP well, offshore East India

Drilling through a narrow pore pressure-fracture pressure window, especially under HTHP (high temperature-high pressure) conditions, is one of the most challenging and costly operations in the oil and gas industry. In this case study, drilling results and thermal stress modelling emphasized the role of thermal stress in several borehole failures encountered at shallow depths and severe formation breakdown incidents at deeper depths. The thermal stress from cooling effects delayed the shear failure conditions by reducing the maximum tangential stress of the formation around the wellbore, but induced formation breakdown as the minimum tangential stress exceeded the tensile strength of the formation. The result from this study shows both the rock stiffness (Young’s Modulus, Poisson Ratio) and differential temperatures (ΔT) have a critical control on thermal stress-related instabilities. Thermal stress-based wellbore stability modelling shows that temperature fluctuations in the dynamic drilling environment can induce a stress change at the rate of 300-500 psi/10°C. Our study results show that the range of thermal stress magnitudes in stiff rocks can vary between 300-4000 psi for a ΔT range of 20-60°C.

Rare Helium-Bearing Compound FeO_{2}He Stabilized at Deep-Earth Conditions.

There is compelling geochemical evidence for primordial helium trapped in Earth's lower mantle, but the origin and nature of the helium source remain elusive due to scarce knowledge on viable helium-bearing compounds that are extremely rare. Here we explore materials physics underlying this prominent challenge. Our structure searches in conjunction with first-principles energetic and thermodynamic calculations uncover a remarkable helium-bearing compound FeO_{2}He at high pressure-temperature conditions relevant to the core-mantle boundary. Calculated sound velocities consistent with seismic data validate FeO_{2}He as a feasible constituent in ultralow velocity zones at the lowermost mantle. These mutually corroborating findings establish the first and hitherto only helium-bearing compound viable at pertinent geophysical conditions, thus providing vital physics mechanisms and materials insights for elucidating the enigmatic helium reservoir in deep Earth.

Nanocarbon-based enhanced squeeze treatment for improved scale management

Oil and gas industry is facing dilemma regarding scale management particularly for offshore production activities in ultra-deep waters under high pressure-high temperature (HPHT) conditions. Scale inhibition squeeze treatment widely employed technique for scale control. However, at HPHT conditions, routine conventional chemistries for scale mitigation are ineffective and unviable. This paper presents promising advantages of employing nanotechnology to enhance conventional scale squeeze treatment. Experimental studies were carried out to examine the potential benefits of using Graphene Oxide (GO) and Carbon nanotubes to increase the adsorption and retention of ETDA scale inhibitor onto reservoir rock in a process coined as ‘Nano-carbon Enhanced Squeeze treatment (NCEST)’. This process involves treating the reservoir rock in the near wellbore region with nanomaterials that rendered increased active surface area for scale inhibitor adsorption. Stronger bonding was witnessed between EDTA and reservoir rock which accounts for better retention of EDTA. Test analysis of coreflood experiments were conducted by the aid of FESEM, EDX and UV-visible. Application of the proposed NCEST model was observed to significantly increase adsorption of EDTA on rock core sample treated with GO to achieve maximum scale inhibitor adsorptive capacity of 180mg/g as compared to 51mg/g when treated without nanomaterial.

A nano-particle based approach to improve filtration control of water based muds under high pressure high temperature conditions

There have been many attempts to improve the filtration control of water based muds under High Pressure High Temperature (HPHT) condition using a cost effective approach. Nano particles are perhaps the best option considering their successful applications reported in many studies. However, they are often expensive and pose unfavourably changes on the rheology of the muds. In this paper, an attempt was made to show the application of Nano Glass Flakes (NGFs) as a cheap but effective nano particle to control the filtration of water based muds under HPHT conditions. Performing a series of rheology, filtration and conductivity tests on the mud samples with unmodified NGFs revealed that this nano particle increases the mud rheology, yield point and gel strength of the mud with a slight impact on the filtration loss. However, by modifying the surface charges of NGFs with a cationic surfactant, filtration loss was significantly reduced without any severe impacts on the mud rheology. Considering the conductivity of the mud which increases by adding the modified NGF, this nano particle might be a good choice to improve the overall performance of water based muds under HPHT conditions.

Enhancing the Stability of Invert Emulsion Drilling Fluid for Drilling in High-Pressure High-Temperature Conditions

Drilling in high-pressure high-temperature (HPHT) conditions is a challenging task. The drilling fluid should be designed to provide high density and stable rheological properties. Barite is the most common weighting material used to adjust the required fluid density. Barite settling, or sag, is a common issue in drilling HPHT wells. Barite sagging may cause many problems such as density variations, well-control problems, stuck pipe, downhole drilling fluid losses, or induced wellbore instability. This study assesses the effect of using a new copolymer (based on styrene and acrylic monomers) on the rheological properties and the stability of an invert emulsion drilling fluid, which can be used to drill HPHT wells. The main goal is to prevent the barite sagging issue, which is common in drilling HPHT wells. A sag test was performed under static (vertical and 45° incline) and dynamic conditions in order to evaluate the copolymer’s ability to enhance the suspension properties of the drilling fluid. In addition, the effect of this copolymer on the filtration properties was performed. The obtained results showed that adding the new copolymer with 1 lb/bbl concentration has no effect on the density and electrical stability. The sag issue was eliminated by adding 1 lb/bbl of the copolymer to the invert emulsion drilling fluid at a temperature >300 °F under static and dynamic conditions. Adding the copolymer enhanced the storage modulus by 290% and the gel strength by 50%, which demonstrated the power of the new copolymer to prevent the settling of the barite particles at a higher temperature. The 1 lb/bbl copolymer’s concentration reduced the filter cake thickness by 40% at 400 °F, which indicates the prevention of barite settling at high temperature.

Spin-induced multiferroicity in the binary perovskite manganite Mn2O3

The ABO3 perovskite oxides exhibit a wide range of interesting physical phenomena remaining in the focus of extensive scientific investigations and various industrial applications. In order to form a perovskite structure, the cations occupying the A and B positions in the lattice, as a rule, should be different. Nevertheless, the unique binary perovskite manganite Mn2O3 containing the same element in both A and B positions can be synthesized under high-pressure high-temperature conditions. Here, we show that this material exhibits magnetically driven ferroelectricity and a pronounced magnetoelectric effect at low temperatures. Neutron powder diffraction revealed two intricate antiferromagnetic structures below 100 K, driven by a strong interplay between spin, charge, and orbital degrees of freedom. The peculiar multiferroicity in the Mn2O3 perovskite is ascribed to a combined effect involving several mechanisms. Our work demonstrates the potential of binary perovskite oxides for creating materials with highly promising electric and magnetic properties.

Shear bond strength of oil well cement in carbonic acid environment

Abstract Shear Bond Strength (SBS) is an important property of cement that determines the life of oil and gas wells. This paper presents the results of an experimental study on the effect of carbonation on the SBS of cement under high-pressure high-temperature (HPHT) condition. The study is aimed at examining the effects of CO2 concentration, temperature, and pressure on SBS of cement containing 35% of silica flour. The study was conducted by aging two types of specimens (i.e. cement cores and SBS samples made of steel pipe and cement). After curing, the specimens were aged for 14 days in an autoclave. The autoclave was 80% filled with brine saturated with mixed gas containing CO2 and CH4. Aging pressure (21–62 MPa), temperature (38–221 °C) and CO2 concentration (10–100% CO2) were varied. After aging, the specimens were recovered, and their SBS, porosity and mineralogical composition were determined to assess the level of carbonation and degradation. To identify the most dominant factor affecting the SBS of cement, measurements were analyzed applying the Analysis of Variance (ANOVA) method. The analysis showed that temperature has a more prominent effect on the carbonation process than pressure and CO2 concentration. Furthermore, results showed strong interaction effect among the main influential factors (pressure, temperature and CO2 concentration). SBS increased with the carbonation. Medium-range temperatures (107 and 177 °C) caused high levels of carbonation as manifested by huge improvement in SBS and a significant reduction in porosity after exposure to a carbonic acid environment.

Covalency is Frustrating: La2Sn2O7 and the Nature of Bonding in Pyrochlores under High Pressure-Temperature Conditions.

Natural specimens of the pyrochlore (A2B2O7) compounds have been found to retain foreign actinide impurities within their parent framework, undergoing metamictization to a fully amorphous state. The response to radionuclide decay identifies pyrochlore systems with having high radiation tolerance and tailored use in radioactive waste applications and radionuclide sequestration. High pressure is a powerful pathway to high density states and amorphization with parallels to radiation-induced processes. Here, La2Sn2O7 is evaluated under extreme conditions via the combination of laser heating in a diamond anvil cell with X-ray diffraction and Raman spectroscopy. The measurements are supported by ab initio random structure searching and molecular dynamics calculations. A new ground state at 70 GPa is revealed, and high temperature annealing is fundamental to access its crystalline ground state and fully determine the structure. This crystalline phase ( P21/ c) retains its structural integrity during decompression and is fully recoverable to ambient conditions. The final state of the system is shown to be highly pathway dependent due to the covalent nature of the Sn-O bonding. The Tc pyrochlore, La2Tc2O7, is analyzed for similarities in the bonding to determine the likelihood of an analogous pathway dependency to a final state.

Nodal-to-nodeless superconducting order parameter in LaFeAs1\u2212xPxO synthesized under high pressure

Similar to chemical doping, pressure produces and stabilizes new phases of known materials, whose properties may differ greatly from those of their standard counterparts. Here, by considering a series of LaFeAs1−xPxO iron-pnictides synthesized under high-pressure high-temperature conditions, we investigate the simultaneous effects of pressure and isoelectronic doping in the 1111 family. Results of numerous macroscopic and microscopic technique measurements unambiguously show a radically different phase diagram for the pressure-grown materials, characterized by the lack of magnetic order and the persistence of superconductivity across the whole 0.3 ≤ x ≤ 0.7 doping range. This unexpected scenario is accompanied by a branching in the electronic properties across x = 0.5, involving both the normal and superconducting phases. Most notably, the superconducting order parameter evolves from nodal (for x < 0.5) to nodeless (for x ≥ 0.5), in clear contrast to other 1111 and 122 iron-based materials grown under ambient-pressure conditions.

Minimum miscibility pressure and interfacial tension measurements for N2 and CO2 gases in contact with W/O emulsions for different temperatures and pressures

In this research, the IFT behavior of two different specimens of W/O emulsion with distinctive soluble ingredients of water in contact with CO2 and N2 was examined. The Minimum Miscibility Pressure (MMP) of the mentioned gases with emulsion specimens were measured and compared with the case of the original crude oil with no water content. This study focuses on the quantity of water in the W/O emulsion specimens and its effects on IFT and MMP values. The IFT behavior of W/O emulsions was surveyed for two different cases of distinctive water soluble ingredients, i.e. sea water and reservoir brine. The tests were performed under high pressure-high temperature (HPHT) conditions utilizing Axisymmetric Drop Shape Analysis (ADSA) procedure. The equilibrium IFT values between the two distinctive specimens of W/O emulsions with different amounts and compositions of dispersed water and two types of gases, i.e. CO2 and N2, were measured. The outcomes were compared with the behavior of original crude oil, i.e. crude oil with no water content. The temperature was set in two distinctive values of 313.15 K and 333.15 K, and the pressure changes in the scope of 1 MPa–20.68 MPa. The outcomes manifested that the IFT behavior of the emulsion could be correlated directly with pressure for two distinctive variation rates, categorized in two different regions. Comparing to the original crude oil, in the case of W/O emulsion the equilibrium IFT increases, and this incremental behavior is much significant in the case of N2-emuslion system. Additionally, the outcomes of IFT versus pressure, in the case of N2-emulsion system, manifested that the slope of the first part of the curve decreases with increment in dispersed water content in the crude oil. However, the IFT values versus pressure in the second region were not affected by the water content of the emulsion. Also, Vanishing Interfacial Tension (VIT) technique was used to estimate the MMP of N2-emulsion systems. According to the outcomes, MMP was increased in the existence of water, and the incremental behavior becomes significant when the water content is increased. It is worthy to note that the outcomes of the CO2-emulsion systems manifested that both IFT behavior and MMP values were not changed significantly by water content. Finally, in light of the test information gathered in this research, various relationships were proposed to express the IFT and MMP correlations as dependants of pressure at distinctive temperatures.

An experimental study to investigate the influence of temperature and pressure on the rheological characteristics of “Glydril” water-based muds

The global demands on oil and gas exploring deep wells are increasing quickly. Drilling at deep and ultra-deep faces a wide range of difficult challenges. One of the challenges is the negative impact on the rheological properties of the drilling fluids when exposed to high temperature high pressure conditions. To operate a drilling operation successfully, the drilling engineer must have a good estimate for the values of rheological properties of drilling fluids, such as viscosity, density, yield point, gel strength etc. In this work, an experiment was conducted on a special type of water-based mud which is called (Glydril), from ambient condition to high temperature and pressure. In this paper, we study the effects of constant pressure (500 psi) and high temperature up to (200°C).

Manifestation of octane rating, fuel sensitivity, and composition effects for gasoline surrogates under advanced compression ignition conditions

Substantial research effort has been spent on the development of advanced compression ignition (ACI) engine combustion strategies over the past decades, including homogeneous charge compression ignition (HCCI), reactivity controlled compression ignition (RCCI), and gasoline direct-injection compression-ignition (GDCI), etc. The behavior of gasoline-type fuels under compression ignition conditions has subsequently attracted extensive experimental and kinetic modeling interest. On the other hand, towards the development of future transportation fuels and engines, the evaluation of general fuel properties, instead of endless testing of specific fuels, should be the future research focus. In this study, the individual roles of the research and motor octane numbers (i.e., RON and MON) and fuel sensitivity (S) in characterizing the ignition performance of gasoline surrogates have been systematically investigated under a typical ACI engine condition using well-validated surrogate and kinetic models. The crank angle corresponding to 50% total heat release (CA50) was utilized as an indicator of the overall fuel reactivity, and iso-contours of CA50 were mapped out in the full engine operating domain characterized by the temperature and pressure at intake valve closing (IVC). By comparing the ignition performance of toluene primary reference fuel blends (TPRF) with the same RON, MON or S values, the distinctive effects and dominant ACI operating conditions of these fuel properties are clearly demonstrated. The role of equivalence ratio is also discussed by comparing the intrinsic stoichiometric condition of the standard octane rating tests and the lean mixture conditions required by ACI operation. The results show that octane sensitivity manifests itself in the high pressure low temperature operating regime for fuels with identical RON or MON, through different low temperature reactivities and heat release rates, while in low pressure high temperature conditions, combustion phasing is less sensitive to all fuel properties, including RON, MON and S. TPRFs with the same sensitivity show the largest variation of CA50 in the intermediate operating conditions, where the thermodynamic traces pass primarily through the ignition delay regime characterized by negative-temperature coefficient (NTC) behavior. Finally, by comparing the combustion phasing of five different gasoline surrogates with nearly identical RON and MON, potential compositional effects for gasoline fuels under ACI condition are further discussed via kinetic modeling. This study also demonstrates that the controlling fuel properties of gasoline-like fuels depend on ACI operating conditions (pressure and temperature trajectory), which should be carefully considered when constructing fuel metrics and comparing experimental results of ACI engines.