Low Load Limit Research Articles

Impact of dissolution medium pH and ionization state of the drug on the release performance of amorphous solid dispersions

Amorphous solid dispersions (ASDs) are widely employed as a strategy to improve oral bioavailability of poorly water soluble compounds. Typically, optimal dissolution performance from a polyvinylpyrrolidone vinyl acetate (PVPVA) based ASD is observed at relatively low drug loading limit. Above a certain drug load, termed limit of congruency (LoC), the release from ASDs significantly decreases. So far, the majority of the dissolution behavior has been tested in conditions where the drug primarily exists in unionized form. In this work, the impact of pH of the dissolution environment on the release performance of ASDs of an ionizable drug was studied. Atazanavir (ATZ), a weakly basic drug with a pKa of 4.5 was used as a model compound and PVPVA was used as a non-ionizable matrix polymer. Dissolution rate was measured using Wood's apparatus which normalizes the surface area of the dissolving tablet. The pH of the dissolution media was varied between 1 and 6.8, to cover a range where ATZ exists as >99 % ionized or unionized species. At pH 6.8, near complete release was observed only when the drug load was ≤ 6 %. Unlike typically observed drastic decline in release behavior for PVPVA based ASDs above LoC, ATZ ASDs underwent gradual decline in dissolution behavior when the DL was increased to 8 %. This was attributed to potential formation of an ATZ-PVPVA associated phase with dissolution rate slower than neat PVPVA. However, the 10 % DL ASD showed negligible ATZ release. On another extreme (pH 1) where ATZ is ∼100 % ionized, the dissolution rate of ATZ was faster than that of PVPVA. ASD dissolution rate was found to be slower than that of the neat drug but faster than PVPVA and interestingly, did not change with DL. This can be attributed to formation of an ionized ATZ-PVPVA phase which controls the dissolution rate of the ASD. At pH 3, where the drug is ∼97 % ionized, near complete release was observed for drug loads ≤ 8 %. To observe significant increase in drug loading with near complete release, >98 % ionization of ATZ was required. At pH 2 where ATZ is ∼99.7 % ionized, near complete release was observed for drug loads up to 30 %. Furthermore, the deterioration in dissolution performance with an increase in drug load continued to be gradual at pH 2. The enhancement in dissolution performance did not correlate with solubility enhancement of ATZ due to ionization. We theorize that the enhancement in the dissolution performance due to ionization is the result of formation of an ionized ATZ-PVPVA phase which increases the hydrophilicity and the miscibility of the ASD. This can help resist water induced phase separation during ASD dissolution and therefore, result in continuous, and congruent dissolution of the drug and polymer.

Evaluation of ammonia-gasoline co-combustion in a modern spark ignition research engine

Ammonia (NH3) is emerging as a potential favoured fuel for longer range decarbonised heavy transport, particularly in the marine sector, predominantly due to highly favourable characteristics as an effective hydrogen carrier. This is despite generally unfavourable combustion and toxicity attributes, restricting end use to applications where robust health and safety protocols can always be upheld. In the currently reported work, a spark ignited thermodynamic single cylinder research engine equipped with gasoline direct injection was upgraded to include gaseous ammonia port injection fuelling, with the aim of understanding maximum viable ammonia substitution ratios across the speed-load operating map. The work was conducted at varied effective compression ratios under overall stoichiometric conditions, with the spark timing re-optimised for maximum brake torque at all stable logged sites. The experiments included industry standard measurements of combustion, performance, and engine-out emissions (including NH3 “slip”). With a geometric compression ratio of 11.2:1, it was found possible to run the engine on pure ammonia at low engine speeds (1000-1800 rpm) and loads of 12 bar net IMEP. When progressively dropping down below this load limit an increasing amount of gasoline co-firing was required to avoid engine misfire. When operating at 1800 rpm and 12 bar net IMEP, all emissions of carbon (CO2, CO, unburned hydrocarbons) and NOx decreased considerably when switching to higher NH3 substitution ratios, with NOx reduced by ~ 45% at 1800 rpm/12 bar when switching from pure gasoline to pure NH3 (associated with longer and cooler combustion). By further increasing the geometric compression ratio to 12.4 and reducing the intake camshaft duration for maximum effective compression ratio, it was possible to operate the engine on pure ammonia at much lower loads in a fully warmed up state (e.g., linear low load limit line from 1000 rpm/6 bar net IMEP to 1800 rpm/9 bar net IMEP). Under all conditions, the indicated thermal efficiency of the engine was either equivalent to or slightly higher than that obtained using gasoline-only due to the favourable anti-knock rating of NH3. Ongoing work is concerned with detailed breakdown of individual NOx species together with measuring the impact of hydrogen enrichment across the operating map.

Enhancement of Low Operating Load Limit and Engine Characteristics by Hydrogen Addition in a Biogas-Fueled Spark-Ignition Engine

Abstract Biogas is a renewable gaseous fuel and has the potential to replace fossil fuels for spark-ignition engines; however, a higher volumetric proportion of CO2 in biogas degrades the engine characteristics significantly. Biogas upgradation techniques are limited by higher fuel costs, and strenuous modifications would be required for improving engine physical parameters. In this study, experimental investigations were performed with hydrogen-enriched biogas to enhance low operating load limit and engine characteristics, and to the best of authors' knowledge, studies related to operating range and low load enhancement by hydrogen addition in biogas fueled engines are not reported in literature. Gaseous-fuels blending setup was developed to fabricate the gaseous fuel mixtures in desired proportions and moderate amounts of hydrogen (5, 10, 20, and 30% by vol.) were blended with biogas. The experiments were conducted on a single-cylinder SI engine operated at the compression ratio of 10:1 and 1500 rpm for stationary applications. It was found that the coefficient of variation (COV) of indicated mean effective pressure decreased from 10% in case of biogas to 8.69, 6, 3.05, and 1.66%, respectively, for 5, 10, 20, and 30% hydrogen cases at 6 N·m loading condition. Low operating load limit enhanced from 6 N·m in case of biogas to 5.3, 2.2, 1.5, and 0.8 N·m, respectively, for 5, 10, 20, and 30% of hydrogen share in the fuel mixture and brake thermal efficiency also improved with hydrogen enrichment. Carbon-based emissions decreased with hydrogen addition, whereas oxides of nitrogen increased but it was well below the baseline case with pure methane. Overall results indicated that hydrogen enrichment enhances the low load limit and engine characteristics of biogas-fueled SI engines for stationary power generation applications in rural areas.

High metal-loaded Cu2O@TM hybrids for melt-spun antibacterial fibers engineered towards medical protective fabrics

Pathogens pose a serious threat to people's lives and health. Cuprous oxide (Cu2O) is widely used in the field of antibacterial fibers, but its large dosage and low loading limit its application. In this work, tourmaline (TM) was used as the inorganic carrier, and the surface treatment such as silanization and radiation carboxylation was carried out, which greatly improved the grafting rate of acrylic acid (AA) and made the Cu2O loading to 0.93 g/g. The prepared spherical Cu2O@TM has a series of antibacterial effects, such as electrostatic adsorption, destruction of cell membrane permeability, and release of reactive oxygen species. Therefore, Cu2O@TM can achieve 96.9% bacteriostatic rate in only 10 min at a concentration of 20 μg/mL, and completely inactivate Escherichia coli within 20 min. In addition, using only 0.4 wt% Cu2O@TM, the antibacterial rate of antibacterial fibers against Escherichia coli and Staphylococcus aureus were both above 99.99%.

Experimental Study on Combustion and Emission Characteristics of Gasoline Compression Ignition Engines Under Cooperative Control of Operating Parameters

Abstract This study investigated the effects of cooperative-control of the start of injection (SOI), excess air ratio (λ), internal exhaust gas recirculation (I-EGR), and intake air temperature (IAT) on the combustion and emission characteristics of gasoline compression ignition (GCI) engines, especially regards to the combustion stability and knock characteristics. And optimizing the GCI engine combustion and emissions through the cooperative control of multiple parameters is the innovation of this research. The results showed that advancing the SOI and increasing the I-EGR ratio can significantly expand the low-load limit, but the heating effect of 20% I-EGR only worked when the SOI was earlier. An appropriate increase of λ could increase the maximum brake thermal efficiency (BTE) to 40.06%, but resulted in high-knock probability and high NOx emissions. Rising the IAT was more effective than advancing the SOI in improving combustion fluctuations, but the knock probability and knock intensity were more sensitive to the early SOI. When the SOI varied from 26 °CA BTDC to 30 °CA BTDC, λ was 1–1.5, the I-EGR ratio was 5%–20%, and the IAT was 40–50 °C; the GCI engine can obtain the balance among high thermal efficiency, high combustion stability, low knock probability, and low emissions.

Mean Waiting Time in Large-Scale and Critically Loaded Power of d Load Balancing Systems

Mean field models are a popular tool used to analyse load balancing policies. In some exceptional cases the waiting time distribution of the mean field limit has an explicit form. In other cases it can be computed as the solution of a set of differential equations. In this paper we study the limit of the mean waiting time E[Wλ] as the arrival rate λ approaches 1 for a number of load balancing policies in a large-scale system of homogeneous servers which finish work at a constant rate equal to one and exponential job sizes with mean 1 (i.e. when the system gets close to instability). As E[Wλ] diverges to infinity, we scale with -log(1-λ) and present a method to compute the limit limλ-> 1- -E[Wλ]/l(1-λ). We show that this limit has a surprisingly simple form for the load balancing algorithms considered. More specifically, we present a general result that holds for any policy for which the associated differential equation satisfies a list of assumptions. For the well-known LL(d) policy which assigns an incoming job to a server with the least work left among d randomly selected servers these assumptions are trivially verified. For this policy we prove the limit is given by 1/d-1. We further show that the LL(d,K) policy, which assigns batches of K jobs to the K least loaded servers among d randomly selected servers, satisfies the assumptions and the limit is equal to K/d-K. For a policy which applies LL(di) with probability pi, we show that the limit is given by 1/ ∑i pi di - 1. We further indicate that our main result can also be used for load balancers with redundancy or memory. In addition, we propose an alternate scaling -l(pλ) instead of -l(1-λ), where pλ is adapted to the policy at hand, such that limλ-> 1- -E[Wλ]/l(1-λ)=limλ-> 1- -E[Wλ]/l(pλ), where the limit limλ-> 0+ -E[Wλ]/l(pλ) is well defined and non-zero (contrary to limλ-> 0+ -E[Wλ]/l(1-λ)). This allows to obtain relatively flat curves for -E[Wλ]/l(pλ) for λ ∈ [0,1] which indicates that the low and high load limits can be used as an approximation when λ is close to one or zero. Our results rely on the earlier proven ansatz which asserts that for certain load balancing policies the workload distribution of any finite set of queues becomes independent of one another as the number of servers tends to infinity.

PH-sensitive micelles self-assembled from star-shaped TPGS copolymers with ortho ester linkages for enhanced MDR reversal and chemotherapy

TPGS approved by FDA can be used as a P-gp inhibitor to effectively reverse multi-drug resistance (MDR) and as an anticancer agent for synergistic antitumor effects. However, the comparatively high critical micelle concentration (CMC), low drug loading (DL) and poor tumor target limit its further clinical application. To overcome these drawbacks, the pH-sensitive star-shaped TPGS copolymers were successfully constructed via using pentaerythritol as the initial materials, ortho esters as the pH-triggered linkages and TPGS active-ester as the terminated MDR material. The amphiphilic star-shaped TPGS copolymers could self-assemble into free and doxorubicin (DOX)-loaded micelles at neutral aqueous solutions. The micelles exhibited the lower CMC (8.2 × 10−5 mg/ml), higher DL (10.8%) and long-term storage and circulation stability, and showed enhanced cellular uptake, apoptosis, cytotoxicity, and growth inhibition for in vitro MCF-7/ADR and/or MCF-7/ADR multicellular spheroids and in vivo MCF-7/ADR tumors via efficiently targeted drug release at tumoral intracellular pH (5.0), MDR reversal of TPGS, and synergistic effect of DOX and TPGS. Therefore, the pH-sensitive micelles self-assembled from star-shaped TPGS copolymers with ortho ester linkages are potentially useful to clinically transform for enhanced MDR cancer treatment.

A comprehensive experimental investigation of low-temperature combustion with thick thermal barrier coatings

Thick thermal barrier coatings (TBCs) have a significant potential to increase thermal efficiency by reducing heat transfer losses. However, in conventional combustion modes, the drawbacks associated with charge heating and higher propensity to knock have outweighed the efficiency benefits. Since the advanced low-temperature combustion (LTC) concepts are fundamentally different from the conventional combustion modes, these penalties do not exist in most of LTCs.The current experimental study shows the feasibility and benefits of thick TBCs with advanced LTC enabled by two different fuels: conventional gasoline and wet ethanol 80 (WE80, i.e., 80% ethanol and 20% water by mass). A total of five pistons were tested, including two metal baselines and three TBC-coated pistons with different thicknesses or surface finishes. A load sweep was conducted with each fuel on each piston within the same constraints. The thick TBCs extends the low load limit by about 15% for both gasoline and WE80 cases. A deterioration of the high load limit was not observed, which implies that the charge heating penalty does not occur in LTCs. The combustion efficiency increased for the thicker TBC by up to 2% points, and the fuel conversion efficiency was increased by up to 4.3%. The gasoline cases experience the largest benefits at low load, while the wet ethanol experiences the largest benefits at mid-to-high load. The intake temperature requirement is successfully reduced by 10–15 K. It is also observed that the dense sealing layer results in a significant improvement to UHC emissions. All of the coated pistons survived the 10–20 h of engine operation with no visual failure.

Adapting load limiter deployment for frontal crash diversity

Objective: Current European restraint systems may not realize their full protection potential in real-world frontal crashes because they are highly optimized for specific conditions. This research sought to quantify the potential benefit of adapting seat belt load limit thresholds to a wider range of occupant and crash characteristics.Methods: Numerical simulations using Hybrid III dummies were conducted to determine how varying load limiter thresholds could affect occupant kinematics and injury outcome in frontal impacts. Occupant–compartment models were developed with a restraint system consisting of a frontal airbag and a 3-point belt with retractor, buckle pretensioner, and load limiting at the shoulder. Load limiting threshold was varied in 5 frontal impact scenarios, covering as wide a range of real frontal crash conditions as possible. The simulated thoracic injury risks were converted into injury probability values using Abbreviated Injury Scale (AIS) 2+ age-dependent thoracic risk curves. These values were then applied to a British real-world frontal impact sample to determine the injury reduction potential of optimized load limiting, taking into account occupant seating position, impact scenario, occupant size, and occupant age and assuming that an appropriate adaptive system was fitted to all cars.Results: In low-severity impacts, a low load limit provided the best chest protection, without increasing risk to other body regions, for both the 50th and 95th percentile dummies in both front seating positions. In high-severity impacts, the low limit was not recommended because it allowed the driver dummy to move into close proximity with the vehicle interior, although there appeared to be some benefit of lower load limiting for the 50th percentile front passenger dummy, due to the increased ride down space in that seating position. Adapting the load limit showed no injury reduction potential for 5th percentile drivers. Utilizing the best load limit threshold in real-world crashes could reduce the number of occupants with AIS 2+ chest injuries from belt loading from 377 to 251 (a 33% reduction), correspondingly reducing the number of occupants with AIS 2+ chest injuries (from all sources) in the whole frontal impact population from 496 to 370. This is a reduction in injury rate from 6.4% to 4.8%.Conclusions: The concept of an adaptive load limiter shows most promise in low-speed frontal crashes where it could lower the AIS 2+ chest injury risk for most front seat occupants, except the smallest of drivers. Generally, adaptive limiters show less potential effectiveness with increased crash severities. Overall, an intelligent adjustment of load limiting threshold could result in a reduction of at least a third of front seat occupants with AIS 2+ chest injuries associated with restraining loads and an overall reduction in AIS 2+ chest injury rate in frontal crashes from 6.4% to 4.8%

An Experimental Investigation on Low Load Combustion Stability and Cold-Firing Capacity of a Gasoline Compression Ignition Engine

Abstract Gasoline compression ignition (GCI) is one of the most promising combustion concepts to maintain low pollutant emissions and high efficiency. However, low load combustion stability and firing in cold-start operations are two major challenges for GCI combustion. Strategies including negative valve overlap (NVO), advanced injection strategies, fuel reforming, and intake preheating have been proposed in order to solve these difficulties; however, the cold start is still an obstacle. The objective of this work is to study effective methods to achieve GCI engine cold start-up. This work combines NVO, in-cylinder fuel reforming, and intake preheating to achieve quick firing under cold-start conditions and the subsequent warm-up conditions. The results show that start of injection (SOI) during the intake stroke yields the best fuel economy, and injection during the compression stroke has the potential to extend the low load limit. Furthermore, SOI during the NVO period grants the ability to operate under engine conditions with cold intake air and coolant. With highly reactive products made by in-cylinder fuel reforming and fast heat accumulation in the combustion chamber, the NVO injection strategy is highly appropriate for GCI firing. An additional assisted technical method, such as intake preheating, is required to ignite the first firing cycle for a cold-start process. With the combination of NVO, in-cylinder fuel reforming, and intake preheating, the GCI engine successfully started within five combustion cycles in the experiment. After the firing process, the engine could stably operate without further intake preheating; thus, this method is appropriate for engine cold-start and warm-up.

Effect of hydrogen peroxide additive on the combustion and emission characteristics of an n-butanol homogeneous charge compression ignition engine

The homogeneous charge compression ignition (HCCI) combustion was conducted on a modified engine to investigate the effect of hydrogen peroxide (H2O2) additive on the combustion and emission characteristics, such as the indicated thermal efficiency (ηi), the total hydrocarbon (THC), the carbon monoxide (CO) and the nitrogen oxides (NOx) emissions. A simulation using CHEMKIN software was also performed to analyze the experimental data. The results indicate that the addition of H2O2 facilitates the formation of hydroxyl (OH) radical and hydroperoxyl (HO2) radical in the cylinder under HCCI mode, which greatly affects the combustion and emission characteristics of the n-butanol HCCI engine. By adding H2O2, ηi increases, NOx emission remains at an ultra-low level, but THC and CO emissions reduce at almost all the test conditions. Especially at the low intake temperature (Tin) or low load condition, the improvements are very obvious, which suggests that addition of H2O2 may extend the low Tin and low load limits of HCCI engines.

Effect of internal exhaust gas recirculation on the combustion characteristics of gasoline compression ignition engine under low to idle conditions

Internal exhaust gas recirculation (iEGR) is one of the effective methods to improve combustion stability of gasoline compression ignition (GCI) engine under low load conditions. However, the heating effect to the ambient gas, the dilution effect to O2 concentration, and the changing of heat capacity, which are caused by introducing iEGR into cylinder, have complicated influences on combustion process. The present work comprehensively investigates the competitive relationship between heating effect and dilution & heat capacity effect on combustion characteristics in GCI engine under different engine loads. Under low load conditions, there is a competitive relationship between heating effect and dilute & heat capacity effect of iEGR on start of combustion (SoC) and burning rate. The burning rate firstly rises and then decreases as iEGR ratio increases from low to high due to the competitive relationship. However, the SoC is controlled by both fuel distribution and the competitive relationship. In addition, under idle conditions, the heating effect plays the dominant role in combustion process and improves the combustion stability. In this way, the low load limit has been successfully extended by using high iEGR ratio. Meanwhile, the idling fuel consumption per unit displacement reaches the same level of commercial vehicles'.

Low-Load Limit in a Diesel-Ignited Gas Engine

The lean-burn capability of the Diesel-ignited gas engine combined with its potential for high efficiency and low CO 2 emissions makes this engine concept one of the most promising alternative fuel converters for passenger cars. Instead of using a spark plug, the ignition relies on the compression-ignited Diesel fuel providing ignition centers for the homogeneous air-gas mixture. In this study the amount of Diesel is reduced to the minimum amount required for the desired ignition. The low-load operation of such an engine is known to be challenging, as hydrocarbon (HC) emissions rise. The objective of this study is to develop optimal low-load operation strategies for the input variables equivalence ratio and exhaust gas recirculation (EGR) rate. A physical engine model helps to investigate three important limitations, namely maximum acceptable HC emissions, minimal CO 2 reduction, and minimal exhaust gas temperature. An important finding is the fact that the high HC emissions under low-load and lean conditions are a consequence of the inability to raise the gas equivalence ratio resulting in a poor flame propagation. The simulations on the various low-load strategies reveal the conflicting demand of lean combustion with low CO 2 emissions and stoichiometric operation with low HC emissions, as well as the minimal feasible dual-fuel load of 3.2 bar brake mean effective pressure.

Low-Load Limit in a Diesel-Ignited Gas Engine

The lean-burn capability of the Diesel-ignited gas engine combined with its potential for high efficiency and low CO 2 emissions makes this engine concept one of the most promising alternative fuel converters for passenger cars. Instead of using a spark plug, the ignition relies on the compression-ignited Diesel fuel providing ignition centers for the homogeneous air-gas mixture. In this study the amount of Diesel is reduced to the minimum amount required for the desired ignition. The low-load operation of such an engine is known to be challenging, as hydrocarbon (HC) emissions rise. The objective of this study is to develop optimal low-load operation strategies for the input variables equivalence ratio and exhaust gas recirculation (EGR) rate. A physical engine model helps to investigate three important limitations, namely maximum acceptable HC emissions, minimal CO 2 reduction, and minimal exhaust gas temperature. An important finding is the fact that the high HC emissions under low-load and lean conditions are a consequence of the inability to raise the gas equivalence ratio resulting in a poor flame propagation. The simulations on the various low-load strategies reveal the conflicting demand of lean combustion with low CO 2 emissions and stoichiometric operation with low HC emissions, as well as the minimal feasible dual-fuel load of 3.2 bar brake mean effective pressure.

3D Conductive Network with High Loading Li2s for High Performance Lithium-Sulfur Batteries

Nowadays, lithium-sulfur (Li-S) batteries have been considered as one of the most promising next-generation rechargeable batteries, owing to their high theoretical specific capacity of 1672 mAh g−1, high energy density of 2600 Wh kg−1, low-cost and abundant resources. However, the commercial application of Li-S batteries is still hindered by several problems, including insulativity of element sulfur, dissolution of polysulfides and large volume expansion. In addition, sulfur cathodes need be paired with metallic lithium, which tends to form dendrites on the anode surface during cycling resulting in safety problems. Therefore, fully lithiated state of sulfur-lithium sulfide (Li2S) is advantageous over sulfur, because it can paired with metal-free anodes (e.g. graphite, silicon and Sn) avoiding safety problems. In addition, Li2S shows a high theoretical specific capacity of 1166 mAh g−1 and a high melting point of 938°C. Moreover, when Li2S convers to S companying with volume shrinkage, which will not only creates enough space for volumetric expansion but also makes the structure more stable. However, similar to sulfur cathode, low conductivity of Li2S, low active material loading and polysulfide dissolution Li2S limit application of Li2S for high performance batteries. Consequently, it is important to introduce Li2S into three dimensional conductive matrix/host for high performance. Herein, we construct a 3D conductive network with high loading Li2S through a facile liquid solution-evaporation. The 3D conductive network not only possesses a hierarchical architecture with abundant macroporous channels and exhibits a high surface area, which provides enough reaction sites to load and stabilize high-loading Li2S, but also improves the electronic conductivity of Li2S and demonstrates pronounced electrochemical performance with enhanced cycle stability and a good capacity retention.

Experimental investigations of gasoline partially premixed combustion with an exhaust rebreathing valve strategy at low loads

This paper investigates the combustion and emission characteristics using a commercial gasoline with Research Octane Number (RON) of 93 on a Partially Premixed Combustion (PPC) engine equipped with a Variable Valve Actuator (VVA) system. The effects of injection timing, internal exhaust gas recirculation (i-EGR) rate and intake pressure on combustion and emissions are studied. The i-EGR was achieved by an extra opening of the exhaust valve during the intake process. The study was conducted at an engine speed of 1500 r/min with cyclic fuel mass from 11.6 to 22.2mg. The operating region for high-efficient, clean and stable gasoline PPC (i.e., COVimep<5%, NOx<0.4g/kWh, Smoke<0.1 FSN, CO and HC as low as possible) was explored and discussed. The results illustrate that proper i-EGR rates with a fixed injection timing of −24°CA ATDC could maintain optimal thermal efficiency while minimizing CO and HC emissions as the engine load decreased from 3.9 to 2.1bar gross indicated mean effective pressure (IMEPg). However, high NOx at higher load was observed and the adoption of earlier injection timing with lower i-EGR rate has the potential to suppress the sharp Smoke increase at lower NOx levels. Improved combustion process can be obtained with later SOI timings as well as higher i-EGR rates as the intake pressure increased. It has been found that the low-load limit of stable gasoline PPC can be extended to 1.5bar IMEPg through the optimization of VVA, injection strategy and intake boosting.

Research on the Effect of ETCI Based HCCI Technology in the Best Fuel Area

Exhaust check point injection compression ignition (ETC� ), the trapped promote internal thermal residues high temperature high pressure jet fuel mixture is one of the most effective methods to achieve homogeneous charge compression ignition (HCCI). This paper is based on the ETCcombustion mode to study the effect of timing heating of the exhaust valve and the cooling effect of the pressure on the combustion process.. Results show that the best fuel economy can start injection of Ca BTDC at 1500r/min, the exhaust valve timing on combustion properties are strongly influenced by the 370, Shan'xi. Using the residual gas coefficient of the exhaust valve timing control, the combustion stage can be controlled indirectly by the intake temperature of the cylinder. In addition, constant pressure, inlet pressure increasing can increase the excess air coefficient decrease the mixture of average air temperature, which can also be control as the key parameters of the combustion phase in some areas. Therefore, the reasonable cooperation between the exhaust valve timing and the pressure pressure can effectively control the combustion process and emission minimization. At 1500r / min, 30 (calcium negative valve overlap (NVO) and 0.18 MPa pressure, the limit of low load and high load limit of HCCI combustion can be reached 0.27 MPa and 0.723 MPa, respectively.

Extension of the Lower Load Limit in Dieseline Compression Ignition Mode

A study to extend the low load limit of the mixture of commercial gasoline and diesel in the compression mode is performed on a single cylinder diesel engine. The additional measures, like intake heating, rebreathing, negative valve overlap, are not employed. By adopting boosting, sweeping the injection pressure and varying the fuel octane number, the minimum fuelling rate and the minimum IMEP gained is compared. Besides, the thermal efficiency and emission results at these operation points are also discussed.The results illustrate that the high intake pressure, the low injection pressure and the low fuel octane number are very effective to extend low load limit. With these strategies, gasoline-type fuels can get the lowest load 0.07MPa IMEP (0.14MPa intake pressure and 20MPa injection pressure) and successfully replace diesel at low load operation points in the compression mode. Increasing the intake pressure and reducing the injection pressure can significantly reduce the minimum fuelling rate and then the minimum IMEP. The minimum IMEP (0.34MPa) of the calibration point on the original engine at test speed (1600rpm) can be achieved by G80 without boosting.The combustion efficiency is influenced by the intake pressure and the injection pressure, however, the ISFC is more dependent on the engine load rather than other factors. If there is more over-lean mixture in cylinder when adjusting the experimental conditions, CO and HC emissions are higher. To satisfy the Euro VI regulation on NOx (<0.4g/kWh), a small amount of EGR is needed to control NOx emission.

Effects of fuel injection parameters on the performance of homogeneous charge compression ignition at low-load conditions

With the objective of enhancing the effectiveness of late fuel injection strategy in extending the low-load limit of homogeneous charge compression ignition engines, a numerical study is conducted to investigate the effects of fuel injection parameters, such as the injection pressure and spray cone angle, on the overall combustion efficiency and CO/NOx emissions. Closed-cycle engine simulations are performed incorporating detailed iso-octane reaction kinetics and combustion submodel based on the spray-interactive flamelet approach. Extensive parametric studies are conducted to provide a detailed map of the combustion efficiency and emission performance. In general, it is found that the in-cylinder charge stratification can be reduced by both an increased injection pressure and a wider spray cone angle, resulting in substantially lower NOx emissions and reasonably high combustion efficiency simultaneously. The present study demonstrates that an optimal adjustment of the two fuel injection parameters can result in significant extension of the low-load limit of homogeneous charge compression ignition through delayed fuel injection strategy.

High prevalence of anti‐hepatitis B core antigen in hepatitis B virus–vaccinated Chinese blood donors suggests insufficient protection but little threat to the blood supply

In East Asia, individuals systematically vaccinated at birth to hepatitis B virus (HBV) are an increasing part of the blood donor population. Their environment presents a high risk of contact with HBV. HBV vaccine efficacy and potential safety risk carried by vaccinated donors were examined. A total of 2028 vaccinated blood donors were recruited in 2012 and 2013 and tested for serologic (hepatitis B surface antigen [HBsAg], antibody to hepatitis B surface antigen [anti-HBs], and antibody to hepatitis B core antigen [anti-HBc]) and molecular (HBV DNA) markers of HBV. HBsAg, anti-HBs, and viral load were quantified. Donors 18 to 21 years systematically vaccinated at birth and 22 to 25 years and older donors had both 30.0% negative serology and 1.8% anti-HBc only but the latter group carried significantly higher prevalence of anti-HBc (p < 0.0001). Anti-HBc, mostly associated with anti-HBs, increased from 10.7% at age 18 to 31.5% at age 25. The level of anti-HBs was significantly higher in anti-HBc-positive donors than in anti-HBs-only donors (p < 0.0001). Samples from 24 donors contained low viral load (25 ± 22 IU/mL), half of them undetected by standard nucleic acid testing (NAT), and were classified as four recent infections, 17 occult HBV infections (OBI), and three primary OBIs. Eighteen of 24 carried anti-HBs; 14 of 15 strains were wild-type Genotype B and one was Genotype C. In an environment of frequent high Genotype B or C viremia, blood donors vaccinated at birth are frequently but mildly infected: asymptomatic and normal alanine aminotransferase level, identified by anti-HBc seroconversion and boosting of anti-HBs. Low viral load and frequent anti-HBs limit transfusion risk.