Natural gas is a fossil fuel that has been used and investigated extensively for use in spark-ignition (SI) and compression-ignition (CI) engines. Compared with conventional gasoline engines, SI ...engines using natural gas can run at higher compression ratios, thus producing higher thermal efficiencies but also increased nitrogen oxide (NO
x
) emissions, while producing lower emissions of carbon dioxide (CO
2), unburned hydrocarbons (HC) and carbon monoxide (CO). These engines also produce relatively less power than gasoline-fueled engines because of the convergence of one or more of three factors: a reduction in volumetric efficiency due to natural-gas injection in the intake manifold; the lower stoichiometric fuel/air ratio of natural gas compared to gasoline; and the lower equivalence ratio at which these engines may be run in order to reduce NO
x
emissions. High NO
x
emissions, especially at high loads, reduce with exhaust gas recirculation (EGR). However, EGR rates above a maximum value result in misfire and erratic engine operation. Hydrogen gas addition increases this EGR threshold significantly. In addition, hydrogen increases the flame speed of the natural gas–hydrogen mixture. Power levels can be increased with supercharging or turbocharging and intercooling. Natural gas is used to power CI engines via the dual-fuel mode, where a high-cetane fuel is injected along with the natural gas in order to provide a source of ignition for the charge. Thermal efficiency levels compared with normal diesel-fueled CI-engine operation are generally maintained with dual-fuel operation, and smoke levels are reduced significantly. At the same time, lower NO
x
and CO
2 emissions, as well as higher HC and CO emissions compared with normal CI-engine operation at low and intermediate loads are recorded. These trends are caused by the low charge temperature and increased ignition delay, resulting in low combustion temperatures. Another factor is insufficient penetration and distribution of the pilot fuel in the charge, resulting in a lack of ignition centers. EGR admission at low and intermediate loads increases combustion temperatures, lowering unburned HC and CO emissions. Larger pilot fuel quantities at these load levels and hydrogen gas addition can also help increase combustion efficiency. Power output is lower at certain conditions than diesel-fueled engines, for reasons similar to those affecting power output of SI engines. In both cases the power output can be maintained with direct injection. Overall, natural gas can be used in both engine types; however further refinement and optimization of engines and fuel-injection systems is needed.
Dual-fuelling in compression–ignition (CI) engines is a mode of combustion where a small pilot injection of high-cetane fuel (i.e. diesel) ignites a premixed high-octane fuel (i.e. methane) and air ...mixture. This allows conventional CI engines to lower their emissions of smoke and nitrogen oxides
(
NO
x
)
while maintaining their high thermal efficiencies. However, poor ignitability of the main fuel–air charge results in increased emissions of unburnt hydrocarbons (HC) and carbon monoxide (CO). Conventional pilot fuels such as diesel and biodiesel (methyl esters transesterified from raw plant oil) have been researched extensively in prior work, showing that in terms of performance and emissions they perform fairly similarly. This is because the physical, chemical and combustion properties of various methyl esters are comparable to those of conventional diesel. In order to reduce these emissions of HC and CO, alternative pilot fuels need to be considered. As fuels employed during normal CI engine operation, both dimethyl ether (DME, a gaseous CI engine fuel) and water-in-fuel emulsions (conventional biodiesel mixed with varying concentrations of water) have shown that they reduce smoke and
NO
x
emissions significantly, while improving combustion quality. In this work, the performance of DME and water-in-biodiesel emulsions as pilot fuels was assessed. It was seen that the water-in-biodiesel emulsions did not perform as well as expected, as increased HC and CO emissions coupled with a mild change in
NO
x
levels was encountered (compared to conventional pilot fuel, in this case neat biodiesel). The emulsions performed very poorly as pilot fuels below a certain BMEP threshold. DME, while producing higher levels of HC and CO than neat biodiesel, managed to reduce
NO
x
significantly compared to neat biodiesel. Emissions of HC and CO, while higher than neat biodiesel, were not as high as levels seen with the emulsions. Thermal efficiency levels were generally maintained with the liquid pilot fuels, with the DME pilot producing comparatively lower levels.
Dual-fuel compression ignition (CI) engine operation with hydrogen is a promising method of using hydrogen gas in CI engines via high-cetane pilot fuel ignition. However, hydrogen dual-fuel operation ...with neat pilot fuels typically produce: high NO
x
emissions; and high combustion chamber pressure rise rates (leading to increased “Diesel knock” tendencies). While water-in-fuel emulsions have been used during normal CI engine operation to cool the charge and slow combustion rates in an effort to reduce NO
x
emissions, these water-in-fuel emulsions have not been tested as pilot fuels during hydrogen dual-fuel combustion. In this work two water-in-biodiesel emulsions are tested as pilot fuels during hydrogen dual-fuel operation. Hydrogen dual-fuel operation generally produces at best comparable thermal efficiencies compared with normal CI engine operation, while the emulsified biodiesel pilot fuels generally increase thermal efficiencies when compared with the neat biodiesel pilot fuel during dual-fuel operation. There is also a clear reduction in NO
x
emissions with emulsified pilot fuel use compared with the neat pilot fuel. The thermal efficiency increase is more apparent at higher engine speeds, while the NO
x
reduction is more apparent at lower speeds. This is due to two conflicting effects (exclusive to emulsified pilot fuel) that occur in tandem. The first is the cooling effect of water vapourisation on the charge, while the second is the microexplosion phenomenon which enhances fuel-air mixing. The NO
x
emission reduction is due to the emulsified pilot fuel lowering pressure rise rates compared with the neat pilot fuel, while the efficiency increase is due to a more homogeneous charge resulting from the violent microexplosion of the emulsified pilot fuel. Smoke, CO, HC and CO
2 emissions remain comparable to neat pilot fuel tests. Overall, emulsified pilot fuels can reduce NO
x
emissions and increase thermal efficiencies, however not at the same instance and under different operating conditions. The general trends of reduced power output, reduced CO
2 and increased water vapour emission during hydrogen dual-fuel operation (with neat pilot fuels) are also maintained.
► Hydrogen and natural gas are tested as fuels in compression ignition engines in the dual fuelling mode, where the gaseous fuels are ignited by diesel and rapeseed methyl ester (RME). ► Engine ...performance and emissions are compared in various operating conditions. ► Overall, CI engines can operate in the dual-fuel mode reasonably successfully with minimal modifications. However, increased NO
x
emissions (with hydrogen use) and incomplete combustion at low and intermediate loads (with natural gas use) are concerns; while port gaseous fuel induction limits power output at high speeds.
This paper presents experimental results of rapeseed methyl ester (RME) and diesel fuel used separately as pilot fuels for dual-fuel compression–ignition (CI) engine operation with hydrogen gas and natural gas (the two gaseous fuels are tested separately). During hydrogen dual-fuel operation with both pilot fuels, thermal efficiencies are generally maintained. Hydrogen dual-fuel CI engine operation with both pilot fuels increases NO
x
emissions, while smoke, unburnt HC and CO levels remain relatively unchanged compared with normal CI engine operation. During hydrogen dual-fuel operation with both pilot fuels, high flame propagation speeds in addition to slightly increased ignition delay result in higher pressure-rise rates, increased emissions of NO
x
and peak pressure values compared with normal CI engine operation. During natural gas dual-fuel operation with both pilot fuels, comparatively higher unburnt HC and CO emissions are recorded compared with normal CI engine operation at low and intermediate engine loads which are due to lower combustion efficiencies and correspond to lower thermal efficiencies. This could be due to the pilot fuel failing to ignite the natural gas–air charge on a significant scale. During dual-fuel operation with both gaseous fuels, an increased overall hydrogen–carbon ratio lowers CO
2 emissions compared with normal engine operation. Power output (in terms of brake mean effective pressure, BMEP) as well as maximum engine speed achieved are also limited. This results from a reduced gaseous fuel induction capability in the intake manifold, in addition to engine stability issues (i.e. abnormal combustion). During all engine operating modes, diesel pilot fuel and RME pilot fuel performed closely in terms of exhaust emissions. Overall, CI engines can operate in the dual-fuel mode reasonably successfully with minimal modifications. However, increased NO
x
emissions (with hydrogen use) and incomplete combustion at low and intermediate loads (with natural gas use) are concerns; while port gaseous fuel induction limits power output at high speeds.
Objective To determine the optimal dose of vitamin D supplementation to achieve biochemical vitamin D sufficiency in extremely low gestational age newborns in a masked randomized controlled trial. ...Study design 100 infants 23 0/7-27 6/7 weeks gestation were randomized to vitamin D intakes of placebo (n = 36), 200 IU (n = 34), and 800 IU/d (n = 30) (approximating 200, 400, or 1000 IU/d, respectively, when vitamin D routinely included in parenteral or enteral nutrition is included). The primary outcomes were serum 25-hydroxy vitamin D concentrations on postnatal day 28 and the number of days alive and off respiratory support in the first 28 days. Results At birth, 67% of infants had 25-hydroxy vitamin D <20 ng/mL suggesting biochemical vitamin D deficiency. Vitamin D concentrations on day 28 were (median 25th-75th percentiles, ng/mL): placebo: 22 (13-47), 200 IU: 39 (26-57), 800 IU: 84.5 (52-99); P < .001. There were no differences in days alive and off respiratory support (median 25th-75th percentiles, days): placebo: 1 (0-11), 200 IU: 0 (0-8), and 800 IU: 0.5 (0-22); P = .63, or other respiratory outcomes among groups. Conclusions At birth, most extremely preterm infants have biochemical vitamin D deficiency. This biochemical deficiency is reduced on day 28 by supplementation with 200 IU/d and prevented by 800 IU/d. Larger trials are required to determine if resolution of biochemical vitamin D deficiency improves clinical outcomes. Trial registration ClinicalTrials.gov : NCT01600430.
This large randomized trial with a 2-by-2 factorial design compared a lower target range of oxygen saturation (85 to 89%) with a higher target range (91 to 95%) in extremely preterm infants. The ...lower target range did not significantly decrease the combined outcome of severe retinopathy or death, but it resulted in an increase in mortality and a substantial decrease in severe retinopathy among survivors.
A lower target range of oxygen saturation did not significantly decrease the combined outcome of severe retinopathy or death, but it resulted in an increase in mortality and a substantial decrease in severe retinopathy among survivors.
Retinopathy of prematurity is an important cause of blindness and other visual disabilities in preterm infants. The incidence of retinopathy of prematurity was increased with exposure to unrestricted oxygen supplementation in preterm infants in randomized, controlled trials performed in the 1950s.
1
In the 1960s, this increase resulted in the practice of restricting the fraction of inspired oxygen (FIO
2
) to no more than 0.50, which was estimated to result in an excess of 16 deaths per case of blindness prevented.
2
More recent data suggest that levels of oxygen saturation previously thought to be at the upper end of the . . .
Objective To test the hypothesis that increasing severity of the fetal inflammatory response (FIR) would have a dose-dependent relationship with severe neurodevelopmental impairment or death in ...extremely preterm infants. Study design We report 347 infants of 23-28 weeks gestational age admitted to a tertiary neonatal intensive care unit between 2006 and 2008. The primary outcome was death or neurodevelopmental impairment at the 18- to 22-month follow-up. Exposure status was defined by increasing stage of funisitis (stage 1, phlebitis; stage 2, arteritis with or without phlebitis; stage 3, subacute necrotizing funisitis) and severity of chorionic plate vasculitis (inflammation with or without thrombosis). Results A FIR was detected in 110 placentas (32%). The rate of severe neurodevelopmental impairment/death was higher in infants with subacute necrotizing funisitis compared with infants without placental/umbilical cord inflammation (60% vs 35%; P < .05). Among infants with stage 1 or 2 funisitis, the presence of any chorionic vasculitis was associated with a higher rate of severe neurodevelopmental impairment/death (47% vs 23%; P < .05). After adjustment for confounding factors, only subacute necrotizing funisitis (risk ratio, 1.87; 95% CI, 1.04-3.35; P = .04) and chorionic plate vasculitis with thrombosis (risk ratio, 2.21; 95% CI, 1.10-4.46; P = .03) were associated with severe neurodevelopmental impairment/death. Conclusion Severe FIR, characterized by subacute necrotizing funisitis and severe chorionic plate vasculitis with thrombosis, is associated with severe neurodevelopmental impairment/death in preterm infants.
Poor food and fluid intake and malnutrition are endemic among older adults in long-term care (LTC), yet feasible and sustainable interventions that target key determinants and improve person-centered ...outcomes remain elusive. Without a comprehensive study addressing a range of determinants to identify those that are of greatest importance for targeting with interventions, expert consensus can be used to develop a research agenda. International experts and stakeholders convened for a 2-day meeting to participate in a nominal group process to identify and prioritize determinants of food and fluid intake for persons living in LTC. Top determinants to address with intervention research included social interactions of residents at mealtime; self-feeding ability; the dining environment; the attitudes, knowledge, and skills of staff; adequate time to eat/availability of staff to provide assistance; sensory properties of the food; hospitality and mealtime logistics; choice and variety in the dining experience; and nutrient density of food. Multimodal interventions that could target these prioritized determinants were also suggested. This consensus process has resulted in a prioritized research agenda for the development and testing of interventions to improve food and fluid intake of older adults living in LTC.
Objective To identify single-nucleotide polymorphisms (SNPs) and pathways associated with bronchopulmonary dysplasia (BPD) because O2 requirement at 36 weeks' postmenstrual age risk is strongly ...influenced by heritable factors. Study design A genome-wide scan was conducted on 1.2 million genotyped SNPs, and an additional 7 million imputed SNPs, using a DNA repository of extremely low birth weight infants. Genome-wide association and gene set analysis was performed for BPD or death, severe BPD or death, and severe BPD in survivors. Specific targets were validated via the use of gene expression in BPD lung tissue and in mouse models. Results Of 751 infants analyzed, 428 developed BPD or died. No SNPs achieved genome-wide significance ( P < 10−8 ), although multiple SNPs in adenosine deaminase, CD44, and other genes were just below P < 10−6 . Of approximately 8000 pathways, 75 were significant at false discovery rate (FDR) <0.1 and P < .001 for BPD/death, 95 for severe BPD/death, and 90 for severe BPD in survivors. The pathway with lowest FDR was miR-219 targets ( P = 1.41E-08, FDR 9.5E-05) for BPD/death and phosphorous oxygen lyase activity (includes adenylate and guanylate cyclases) for both severe BPD/death ( P = 5.68E-08, FDR 0.00019) and severe BPD in survivors ( P = 3.91E-08, FDR 0.00013). Gene expression analysis confirmed significantly increased miR-219 and CD44 in BPD. Conclusions Pathway analyses confirmed involvement of known pathways of lung development and repair (CD44, phosphorus oxygen lyase activity) and indicated novel molecules and pathways (adenosine deaminase, targets of miR-219) involved in genetic predisposition to BPD.
An evidence gap exists regarding the role of endotracheal secretions in pediatric extubation decisions. This study aims to evaluate whether endotracheal secretion burden independently correlates with ...pediatric extubation failure.
This is a single-center, prospective cohort study of children aged <19 years requiring intubation. Nurses (RN) and respiratory therapists (RT) independently used a novel secretion assessment score focusing on secretion volume, character, and trend. We hypothesized that the RN and RT secretion scores would not correlate with extubation outcome and inter-rater reliability would be poor.
RN secretion character sub-score (OR 3.3, 95% CI 1.1-11.1, p = 0.048) was independently associated with extubation failure. RN and RT inter-rater reliability was poor (correlation 0.385, 95% CI 0.339-0.429, p < 0.001). A failure prediction model incorporating the RN secretion character sub-score as well as indication for mechanical ventilation and spontaneous breathing trial result demonstrated an area under the receiver operating curve of 0.817 (95% CI 0.730-0.904, p < 0.001).
In the general pediatric population, the RN assessment of endotracheal secretion character was independently associated with extubation failure. A model incorporating indication for mechanical ventilation, spontaneous breathing result, and RN assessment of endotracheal secretion character demonstrated reasonable accuracy in predicting failure in those clinically selected for extubation.
Development of comprehensive and sensitive extubation readiness bundles are key to balancing the competing risks of prolonged invasive mechanical ventilation duration and extubation failure. Evidence for clinical factors linked to extubation outcomes in children are limited. Endotracheal secretion burden is a common factor considered but has not been studied. This study supports a role for endotracheal secretion burden, as assessed by the bedside nurse, in extubation readiness bundles. Inter-rater reliability with respiratory therapists was poor. A model incorporating other key factors showed good discrimination for extubation outcome and sets the stage for prospective evaluation in the general population and diagnosis-specific subgroups.
PDF
