Incomplete Combustion Research Articles

Experimental and numerical study on data-driven prediction for wildfire spread incorporating adaptive observation error adjustment

In recent wildfire prediction research, data assimilation (DA) methods like Ensemble Kalman filtering have gained traction for integrating observation data to enhance prediction accuracy. Most previous studies trusted that the observation data were accurate, and set a small observation error, which causes unreliable predicted results for scenarios with large observation error. To tackle this, our study introduced a method that iteratively adjusted the potential range of observation errors by comparing observation and simulation data over time. We conducted a 30-m experiment and kilometer-scale numerical simulations. Unlike prior research, we adopted larger error ranges (the similarity index with true data ranges from 0.6 to 1) for both real and synthetic observation data. In the experiment, to increase the complexity of fire spread, a heterogeneous fuel arrangement was employed. Irregular flame fronts appeared due to incomplete combustion and were difficult to replicate in simulations. Better accuracy was achieved using real observation data to revise predictions. Furthermore, to improve the applicability of the algorithm, numerical simulations were designed to consider observation error changing over time or not. The Root Mean Square Errors for the fire front prediction using the proposed method remained lower than that of the traditional DA approach.

STUDYING HOW DIESEL ENGINE ADDITIVES USING SILVER OXIDE (Ag2O) NANOPARTICLES AFFECT THE ENVIRONMENT

Abstract: Biodiesel has been defined as an alternative fuel that has the potential to be used instead of diesel fuel for years. In case of complete combustion reaction in engines, the products released do not directly threaten human health. Compared to diesel fuel, biodiesel has worse combustion performance due to some fuel properties. Therefore, incomplete combustion products such as hydrocarbon (HC), carbon monoxide (CO), nitrogen oxide (NOx), smoke emission and complete combustion products such as CO2 are thrown into the atmosphere. In this study, the changes in exhaust emissions of 50 ppm and 75 ppm Ag2O NPs were experimentally examined to improve the adverse combustion performance and emission characteristics of cottonseed oil methyl ester. In experiments, nano additive improved the thermal conductivity, mass dissipation and heat transfer of the test fuels, and resulted in reducing of CO emissions as it provided a higher oxidation rate of hydrocarbon molecules. Due to the improvement in the combustion reaction, CO2 emission increased with product of complete combustion. The increase in CO2 emissions was 3.17% and 3.97% for CAg-50 and CAg-75 fuels, respectively, when compared to C0 fuel at 40 Nm load. The NPs additive increased the lower calorific value of the fuel and cylinder temperature. This situation caused increase of NOx emissions by 3.69% and 7.47% CAg-50 and CAg-75 fuels 40 Nm load. Adding of NPs in base fuel reduced to viscosity and density provided better atomization. So a reduction in smoke emission was obtained with NPs addition by 35.09% and 47.32% in CAg-50 and CAg-75 fuels, respectively, compared to C0 fuel at 10 Nm load, while 7.45% and 19.43% at 40 Nm load.

Interactions between phenanthrene exposure and historical chemical stress: Implications for fitness and ecological resilience of the sentinel species Daphnia magna

Polycyclic aromatic hydrocarbons (PAHs) arise from incomplete combustion of oil, coal, and gasoline, with lipophilic properties facilitating their widespread distribution and persistence. Due to their biochemical attributes, PAHs can accumulate in animal tissues, potentially causing mutagenic and carcinogenic effects. Since the industrial revolution, PAH concentrations in the environment have risen, with lakes showing levels from 0.159 to 33,090 μg/kg sediment. Despite acute toxicity studies showing adverse effects on freshwater organisms, the long-term impacts and synergistic interactions with other pollutants remain largely unexplored.This study investigates the impact of phenanthrene (PHE), a prominent PAH found in aquatic environments, on Daphnia magna, a species of significant ecological importance in freshwater ecosystems globally, being both a sentinel species for chemical pollution and a keystone organism in freshwater aquatic ecosystems. Leveraging the dormancy of D. magna, which spans decades or even centuries, we exposed strains with diverse histories of chemical contaminant exposure to environmentally relevant concentrations of PHE. Initially, acute exposure experiments were conducted in accordance with OECD guidelines across 16 Daphnia strains, revealing substantial variation in acute toxic responses, with strains naïve to chemical pollutants showing the lowest toxicity. Utilizing the median effect concentration EC10 derived from acute exposures, we assessed the impacts of chronic PHE exposure on life history traits and ecological endpoints of the 16 strains. To elucidate how historical exposure to other environmental stressors may modulate the toxicity of PHE, temporal populations of D. magna resurrected from a lake with a well-documented century-spanning history of environmental impact were utilized. Our findings demonstrate that PHE exposure induces developmental failure, delays sexual maturation, and reduces adult size in Daphnia. Populations of Daphnia historically exposed to chemical stress exhibited significantly greater fitness impacts compared to naïve populations. This study provides crucial insights into the augmented effects of PAHs interacting with other environmental stressors.

OH radical and Cl atom initiated Reactions of Methyl n-propyl ether: Kinetics and Atmospheric Implications

Oxygenated volatile organic compounds (OVOCs) are emitted into the atmosphere via biological processes, oxidation of hydrocarbons, evaporation of oxygenated solvents or fuels and incomplete combustion of hydrocarbon-fueled sources. In the troposphere, the degradation mechanisms of these VOCs are triggered by oxidising agents like Cl atoms and OH radicals. In the present work, the kinetics were investigated for the reactions of methyl n-propyl ether (MPE) with OH radicals and Cl atoms using pulsed laser photolysis-laser induced fluorescence and relative rate techniques, respectively, in the range of 278–363 K. No significant temperature-dependence was observed for the reaction of MPE with OH radicals, whereas a slight negative temperature-dependence was asserted in the Cl reaction. The rate coefficients were also determined computationally at the CCSD(T)/aug-cc-pVDZ//M06-2X/6-311+G(d,p) and CCSD(T)/6-31+G(d,p)//BHandHLYP/6-31+G(d,p) level of theories over 250–400 K for the OH- and Cl-initiated reactions of MPE, respectively. The Arrhenius expressions for the title reactions determined are: kMPE+OHPLP−LIF(T=278−363K)=(1.36±0.21)×10−11exp[(−86±48)T] cm3 molecule−1 s−1 and kMPE+ClRR(T=278−363K)=(2.97±0.49)×10−11exp[(617±51)T] cm3 molecule−1 s−1. The rate coefficients were estimated using SAR and compared to the experimentally and computationally determined kinetic data. The products formed in the reactions were detected using the GC-MS. The atmospheric lifetimes of MPE were estimated, accounting for the rate coefficients of both reactions. The impacts of MPE emissions on the atmosphere are discussed using important atmospheric parameters.

Numerical investigation of the hydrogen-enriched ammonia-diesel RCCI combustion engine

Incorporating hydrogen into the fuel blend of ammonia/diesel in reactivity controlled compression combustion (RCCI) engines, while maintaining high indicated mean effective pressure (IMEP) and combustion efficiency (CE), presents a promising approach for mitigating nitrogen oxides (NOx), carbon monoxide (CO), hydrocarbons (HC), unburnt ammonia emissions and nitrous oxide (N2O) greenhouse gas (GHG)-a pressing challenge in the field. By supplementing ammonia/diesel combustion with hydrogen, potential issues related to incomplete combustion can be mitigated, along with a reduction in intake valve close temperature (TIVC). This study aims to assess the impact of hydrogen enrichment on combustion characteristics in RCCI engines utilizing ammonia and diesel as fuels, employing the kinetic mechanism of combustion reactions within Converge software. The effect of TIVC on key engine parameters, including in-cylinder pressure, heat release rate (HRR), CE, IMEP, and exhaust emissions, are analyzed by considering chemical reaction pathways. The findings reveal that introducing hydrogen into the ammonia /diesel RCCI combustion blend, leads to significant enhancements in CE and IMEP while simultaneously lowering emissions of CO, HC, unburnt ammonia, and N2O greenhouse gas (GHG). Specifically, when utilizing 80 % ammonia energy fraction (AEF) without hydrogen, minimum TIVC of 440 K is necessary to prevent incomplete combustion, increasing NOx emissions by approximately 20 g/kWh. However, by addition of 20 % hydrogen energy fraction (HEF) into the fuel mixture, the TIVC requirement drops to 380 K, thereby reducing NOx emissions to around 13 g/kWh, while maintaining consistent level of N2O GHG (2.7 g/kWh).

Numerical study of the combustion process and NOx evolution mechanism of ammonia-hydrogen compound fuel engine under different intake conditions

To explore the distinction between generation atmosphere of fuel NOx and thermal NOx in an ammonia-hydrogen compound fuel engine, a numerical calculation model was established based on a detailed ammonia-hydrogen oxidation mechanism. The combustion process and NOx evolution mechanism of the ammonia-hydrogen compound fuel engine under different intake conditions were studied. The researchresults for different equivalence ratios show that the in-cylinder hydrogen volume is the primary factor influencing the initial heat release. When the equivalence ratio is between 0.89 and 1.14, the mixture exhibits a higher combustion rate, leading to a shorter CD and an earlier CA50. At this point, the heat release process closer to TDC contributes improving engine combustion efficiency and indicated efficiency. Therefore, when the equivalence ratio is between 0.89 and 1.00, combustion efficiency is higher than 98 % and indicated efficiency is higher than 43 %, the ammonia-hydrogen compound fuel engine achieves relatively higher economy. Both over-rich and over-dilute mixtures induce an enhancement of fuel NOx, while the higher in-cylinder temperature caused by stoichiometric combustion leads to a boom of thermal NOx. Consequently, the total NOx emission from the ammonia-hydrogen compound fuel engine is higher at equivalence ratios between 0.80 and 1.00, and the NOx emission reaches its peak at an equivalence ratio of 0.89. Analysis of the evolution process of key N components in the cylinder shows that incomplete combustion plays a significant role in fuel NOx emissions, while thermal NOx emissions are mainly influenced by the distribution of in-cylinder components and combustion temperature. Specifically, thermal NOx emissions primarily depend on the in-cylinder components distribution in the narrow equivalence ratio range around stoichiometric ratio, and are significantly affected by in-cylinder temperature under other conditions. The in-cylinder oxygen concentration significantly affects fuel NOx emissions under most operating conditions. Further optimization of intake temperature shows that combustion efficiency exceeds 90 % when the intake temperature is above 280 K. When the intake temperature reaches 310 K, the combustion efficiency reaches up to 98 %, thus an intake temperature of about 310 K is sufficient to meet the need for improving the combustion efficiency of ammonia-hydrogen compound fuel engine. To achieve high efficiency and lower NOx emissions, appropriate lean combustion combined with an intake temperature slightly above room temperature is recommended.

A novel swiss-roll counterflow micro-combustor: Experimental investigation of methane-oxygen flame behavior over time

This study introduces a novel Swiss-roll micro-combustor design that employs a non-premixed counterflow flame for efficient and stable micro-combustion. This design addresses practical system challenges by (1) stabilizing the flame, (2) enhancing heat recovery and gas preheating, (3) aligning gas momentum with the exhaust, and (4) minimizing disruptive fluid motion within the channels. This research investigates the dynamic behavior and combustion characteristics of a methane-oxygen flame within the combustor across a range of equivalence ratios (1.50–3.38). A synergistic approach combining flame dynamics analysis, spectroscopy, and RGB image processing explores the interplay between flame temperature, strain rate, and equivalence ratio. The results demonstrate the effectiveness of the RGB method as a cost-efficient tool for predicting variations in C2∗ and CH∗ radicals and light-intensity radiations. While flame thickness and length exhibit complex dependencies on the fuel-to-oxygen ratio and wall temperature, specific radical emissions vary dynamically with the equivalence ratio. Notably, equivalence ratios of 1.94 and 2.26 exhibit minimal temporal variations in flame properties, suggesting optimal stability and predictability for practical applications. The investigated flame is classified as a “cool flame,” and efficiency declines with richer mixtures due to increased exhaust heat loss and incomplete combustion. This work paves the way for further micro-combustor design optimization and unlocks the potential of non-premixed counterflow flames in diverse micro-scale applications.

Potential of 14C-based vs. ΔCO-based ΔffCO2 observations to estimate urban fossil fuel CO2 (ffCO2) emissions

Abstract. Atmospheric transport inversions are a powerful tool for independently estimating surface CO2 fluxes from atmospheric CO2 concentration measurements. However, additional tracers are needed to separate the fossil fuel CO2 (ffCO2) emissions from non-fossil CO2 fluxes. In this study, we focus on radiocarbon (14C), the most direct tracer of ffCO2, and the continuously measured surrogate tracer carbon monoxide (CO), which is co-emitted with ffCO2 during incomplete combustion. In the companion paper by Maier et al. (2024), we determined discrete 14C-based and continuous ΔCO-based estimates of the ffCO2 excess concentration (ΔffCO2) compared with a clean-air reference for the urban Heidelberg observation site in southwestern Germany. The ΔCO-based ΔffCO2 concentration was calculated by dividing the continuously measured ΔCO excess concentration by an average 14C-basedΔCO/ΔffCO2 ratio. Here, we use the CarboScope inversion framework adapted for the urban domain around Heidelberg to assess the potential of both types of ΔffCO2 observations to investigate ffCO2 emissions and their seasonal cycle. We find that, although they are more precise, 14C-based ΔffCO2 observations from almost 100 afternoon flask samples collected in the 2 years of 2019 and 2020 are not well suited for estimating robust ffCO2 emissions in the main footprint of this urban area, which has a very heterogeneous distribution of sources including several point sources. The benefit of the continuous ΔCO-based ΔffCO2 estimates is that they can be averaged to reduce the impact of individual hours with an inadequate model performance. We show that the weekly averaged ΔCO-based ΔffCO2 observations allow for a robust reconstruction of the seasonal cycle of the area source ffCO2 emissions from temporally flat a priori emissions. In particular, the distinct COVID-19 signal – with a steep drop in emissions in spring 2020 – is clearly present in these data-driven a posteriori results. Moreover, our top-down results show a shift in the seasonality of the area source ffCO2 emissions around Heidelberg in 2019 compared with the bottom-up estimates from the Netherlands Organization for Applied Scientific Research (TNO). This highlights the huge potential of ΔCO-based ΔffCO2 to validate bottom-up ffCO2 emissions at urban stations if the ΔCO/ΔffCO2 ratios can be determined without biases.

The Effect of Avgas and Ethanol Fuel Mixture on Fuel Spray Temperature

This research aims to examine the effect of the avgas-ethanol fuel mixture on the fuel spray temperature. The research was carried out using a pressurized tube which was sprayed into the mock up which was assumed to be an aircraft combustion chamber with a pressure of 2 bar and a distance of 7,73 cm which would later be sprayed using pure avgas, a mixture of avgas and ethanol namely A80E20 and A60E40 then added with a temperature sensor at the end nozzle, center of jet, and impact wall. The spray temperature can result in incomplete combustion and result in higher exhaust emissions and also damage to the engine if it does not match the temperature capacity of the combustion chamber walls. The spray temperature results for the A60E40 fuel mixture are the lowest temperature, namely 25o-18.2oC and knowing that the more fuel is mixed, the lower the temperature of the fuel.

Characteristics of Nanoparticles in Late Pliocene Paleo-Mountain Fire Relics in Jinsuo Basin, Yunnan Province and Their Implications for Paleoclimate Evolution

Wildfires significantly affect climate and environmental changes, closely tied to extreme weather responses. Vegetation combustion emits greenhouse gases (CO2, CH4, CO), warming the climate. Climate shifts, in turn, impact vegetation growth, altering combustible material types and quantities, thus affecting wildfire intensity, duration, and frequency. Wildfires profoundly affect ecosystems, influenced by factors like atmospheric oxygen and climate. Their combustion gases impact climate and vegetation growth. Recent advancements in studying ancient wildfires include analyzing nanoparticles as key indicators. This study discovered six types of nanoparticles in ancient wildfire remains, with sizes ranging from 50 nm to 500 nm and diverse compositions including elements such as C, O, Mg, Al, Ti, Fe, S, Ca, and P. These findings indicate that wildfires generate a variety of nanoparticles, offering new insights into ancient fire events. Elemental analysis revealed low magnesium but high calcium and aluminum levels, suggesting a warm, humid paleoclimate during these fires. The presence of high Ti-O ratios and carbon-rich nanoparticles points to ground fires with incomplete combustion. This research underscores the significance of nanoparticles in understanding the history and characteristics of ancient wildfires.

Analisis Laju Emisi Gas Buang Karbon Monoksida (Qco) Pada Udara Ambient di Jalan Lintas Mendalo Darat Kabupaten Muaro Jambi

Carbon monoxide (CO) is a compound that has no smell, taste or color. The compound carbon monoxide (CO) originates from vehicle exhaust emissions from incomplete engine combustion, when exposed it will have an impact on disrupting the path of oxygen binding to hemoglobin in the blood. The Mendalo Darat road is one of the busiest roads in Jambi Province, so it is prone to traffic jams due ti the dense mobilization of motorized vehicles. This can result in a decrease in ambient air quality due to the concentration of carbon monoxide (CO) compounds. This study aims to determine the quality of ambient air in the parameters of carbon monoxide (CO) on the Mendalo Darat highway and the resulting emission rate. Based on the research results for 3 days, namely Sunday (Weekend), Monday, and Tuesday (Weekday), it shows that the highest density is on Tuesday morning which is 17,994 units. Meanwhile, the lowest vehicle volume was on Sunday afternoon point III with a vehicle volume of 6.576 units. The results showed that the highest carbon monoxide (Qco) emission rate on Sunday was at point I in the afternoon of 97.114 µg/m.s, at point II in the afternoon that was 52.665 µg/m.s, and point III in the afternoon wa 52.644 µg/m.s. on Monday, the highest emission rate of carbon monoxide (Qco) was at point I in the afternoon of 106.830 µg/m.s. followed by point II in the afternoon, which was 86.795 µg/m.s on Tuesday, and point III, which was 86.749 µg/m.s. on Tuesday, point I with the largest carbon monoxide (Qco) emission rate was 114.290 tn the morning, followed by point I, which was 109.601 in the afternoon

Analysis of electromagnetic and radiative heat source on tangential hyperbolic fluid under Arrhenius kinetic with convective cooling

The global threat of environmental degradation from harmful waste discharge is evident, leading to unusual diseases and natural disasters. Some of these toxic emissions result from human activities, such as the incomplete combustion of hydrocarbons. As such, this study aims to explore the analysis of electromagnetic and radiative heat sources on tangential hyperbolic fluid under Arrhenius kinetic with convective cooling. The transformed momentum and heat equations are solved using a rigorous computational approach called the Galerkin integration approximation with weighted residual method. This computational methodology ensures the reliability and accuracy of the results. Various graphs illustrate the results, showing parametric sensitivity profiles for the velocity, temperature, skin friction, thermal gradient, Bejan, and entropy generation. As noticed from the outcomes, electric field loading increases heat dispersion by about 3.25 % as heat source terms are enhanced. Increasing magnetic field, radiation, and electric field loading parameters strengthened thermodynamic equilibrium and minimized entropy generation. The tangential hyperbolic combustion process is 6.11 % increased with rising Brinkman number and electric field loading terms. The flow rate and temperature field are increased to the peak along the middle of the channel for increasing pressure gradient.

Online SPE-LC-MS-MS method for eight hydroxylated metabolites of polycyclic aromatic hydrocarbons in urine and determination of optimal sampling time after firefighter training

Polycyclic aromatic compounds (PAHs) are formed during incomplete combustion and firefighters are inadvertently at risk of being exposed to these and other hazardous compounds. Exposure to PAHs is often estimated by measuring their hydroxylated metabolites (OH-PAH) in urine. Here, an online-SPE LC-MS-MS method was set up for eight OH-PAHs thus increasing sample throughput and minimizing manual handling. The method was validated over a 5-month period and showed good reproducibility with intra- and inter-day variation of 2.4–8.1 % and 1.6–6.5 %, respectively, of low-level samples and accuracy (91.6–104.8 %) for a standard reference material. The method was applied to urine samples from conscripts training to become firefighters to determine the optimal sampling time for this training activity before a large intervention study. In total, six conscripts sampled urine 6–8 times over a 40-hr period during a 3-day training course. All eight metabolites were detected in ≥ 97 % of the samples and showed peak excretion 4–6 hrs after the training corresponding to 8–10 hrs after first exposure. Samples taken the morning after the exercise contained low levels of most metabolites. Consequently, 4–6 hrs post exposure is recommended as the optimal sampling time for quantification of PAH exposure and monitoring of potential differences in exposure.

Synthesis and Analysis of Activated Carbon Structure from Ketaping Fruit Shell Biomass Through X-Ray Diffraction Characterization

Synthesis of activated carbon from ketaping fruit shell biomass aims to produce high-quality active carbon to be applied in various fields. Activated carbon from ketaping fruit shells is synthesized by thermal treatment. It is synthesized through two stages, namely carbonation and activation. The carbonation stage is carried out at 400oC under O2 gas flow. This aims to break down lignol cellulose into carbon with low-quality pores through incomplete combustion. The activation stage is carried out by mixing activated carbon and KOH in varying ratios of 1:1, 1:3 and 1:5 wt. It is carried out by multilevel thermal treatment at 700oC for 3.5 hours to form activated carbon with high pore quality. The activated carbon produced is then subjected to EDS characterization to see the active carbon content and XRD to see the structure of the active carbon with the characteristics of distance between layers, layer height, layer width, and number of layers. The results of EDX analysis show that the active carbon from the shell of the ketaping fruit contains 97.52% carbon and 2.48% oxygen. The results of XRD analysis show that the activated carbon surface area optimum at a molar ratio of 1:3 wt is 1,708.62 mg-1. The distance of the resulting activated carbon layer is 0.3566nm at the 002 peak and 0.2102nm at the 100 peak. The layer height and width of the active carbon layer produced at a 1:3 wt ratio were 0.5489nm and 0.3002nm. Meanwhile, the number of layers of active carbon produced is 3 layers.

SURFACE MODIFICATION OF FLY ASH FROM ASAM-ASAM COAL POWER PLANT USING STEARIC ACID AS HYDROPHOBIC INORGANIC MATERIAL

Abundant coal reserves make this material a substitute fuel choice, especially for industry. The use of coal carries a high risk due to incomplete combustion and produces fly ash products. Fly ash cause pollution and health risks as well as environmental contamination when they are released, deposited, or leached into the ecosystem over short or long periods of time. The high content of silica and alumina in fly ash can be utilized and modified into new materials with added value. This research aims to modify the surface of fly ash using stearic acid as a hydrophobic inorganic material. Fly ash from Asam-asam Coal Power Plant was characterized by using XRD and modified by immersing in stearic acid (2,4,6, and 8%) and 98% ethanol. The result showed that the contact angle increases when fly ash is modified on the surface using stearic acid. The contact angle increases with increasing stearic acid concentration. The highest contact angle was obtained at a stearic acid concentration of 8%, and the lowest at 2% was about 112.9 and 102.2, respectively. The fly ash composition was primarily silica and alumina, which were crystalline, as confirmed by XRD. These findings provide several aspects of fly ash and its potential as a candidate material for environmental remediation and waste management.

Formation of Products of Incomplete Destruction (PID) from the Thermal Oxidative Decomposition of Perfluorooctanoic Acid (PFOA): Measurement, Modeling, and Reaction Pathways.

The thermal decomposition of perfluorooctanoic acid (PFOA) under oxidative conditions was investigated using air (O2) and N2O as oxidants over temperatures ranging from 400 to 1000 °C in an α-alumina reactor. In the presence of air, PFOA was found to decompose into perfluorohept-1-ene (C7F14) and perfluoroheptanoyl fluoride (C7F14O) in addition to HF, CO, and CO2. At temperatures above 800 °C, both C7F14 and C7F14O were no longer detected. A comprehensive analysis of the reaction mechanisms through quantum chemical analysis and kinetic modeling in combination with experimental observations was utilized to identify key reaction pathways. Quantum chemical analysis led to the conclusion that oxygen atoms are crucial in decomposing perfluoroalk-1-enes, especially the stable perfluorohept-1-ene (C7F14). Under oxidative conditions, it was found that significant quantities of C2F6 and CF4 were formed. Further quantum chemical analysis suggests that the O atoms facilitate the formation of volatile fluorinated compounds (VFCs) such as tetrafluoromethane (CF4) and hexafluoroethane (C2F6), particularly at higher temperatures. By elucidating these key reactions, an improved understanding of the potential formation products of incomplete combustion (PICs) or products of incomplete destruction (PIDs) is made.

Evaluating potential of increasing flow intensity and reducing crevice volume to improve thermal efficiency and hydrocarbon emission in spark-ignition natural gas engines

Low thermal efficiency and high hydrocarbon emissions caused by slow combustion rates and high methane emissions hinder the development of natural gas (NG) engines. Engine structure modifications have always been an important means of improving the combustion effects of engines. This study investigates the effects of combustion chamber improvements on the thermal efficiency and hydrocarbon emissions of stoichiometric spark-ignition NG engines through numerical simulations. The improvements aimed to enhance squish flow, organize high tumble flow, and reduce crevice volume. The results indicate that strengthening the squish intensity by increasing the squish area of the piston can accelerate flame propagation and reduce exhaust loss. However, this improvement is hindered by a significant rise in heat transfer loss, which limits further gains in thermal efficiency. Compared to the traditional high swirl combustion chamber, a high tumble combustion chamber (dual straight intake port combined with a hemispherical piston) can promote flame propagation in the early stages of combustion and increase thermal efficiency by 1.43%. However, the accelerated flame propagation rate resulting from increased flow intensity has little potential to reduce hydrocarbon emissions due to the small contribution of flame quenching to unburned hydrocarbon production. The primary source of hydrocarbon emissions from NG engines is unburned methane in the piston crevice. Therefore, when addressing hydrocarbon emissions from NG engines, the first consideration should be to minimize the volume of the piston crevice, which will significantly reduce methane emissions and incomplete combustion loss.

Associations between urinary hydroxylated polycyclic aromatic hydrocarbon biomarker concentrations and measures of timing of delivery and infant size at birth

Preterm birth is a leading cause of neonatal mortality and presents significant public health concerns. Environmental chemical exposures during pregnancy may be partially to blame for disrupted delivery timing. Polycyclic aromatic hydrocarbons (PAHs) are products of incomplete combustion, exposure to which occurs via inhalation of cigarette smoke and automobile exhaust, and ingestion of charred meats. Exposure to PAHs in the US population is widespread, and pregnant women represent a susceptible population to adverse effects of PAHs. We aimed to investigate associations between gestational exposure to PAHs and birth outcomes, including timing of delivery and infant birth size. We utilized data from the PROTECT birth cohort where pregnant women provided spot urine samples at up to three study visits (median 16, 20, and 24 weeks gestation). Urine samples were assayed for eight hydroxylated PAH concentrations. Associations between PAHs and birth outcomes were calculated using linear/logistic regression models, with adjustment for maternal age, education, pre-pregnancy BMI, and daily exposure to environmental tobacco smoke. Models accounted for urine dilution using specific gravity. We also explored effect modification by infant sex. Interquartile range (IQR) increases in all averaged PAH exposures during the second trimester were associated with reduced gestational age at delivery and increased odds of overall PTB, although these associations were not statistically significant (p > 0.05). Most PAHs at the second study visit were most strongly associated with earlier delivery and increased odds of overall and spontaneous PTB, with visit 2 2-hydroxynapthalene (2-NAP) being significantly associated with increased odds of overall PTB (OR:1.55; 95 %CI: 1.05,2.29). Some PAHs resulted in earlier timing of delivery among only female fetuses, specifically 2-NAP on overall PTB (female OR:1.52 95 %CI: 1.02,2.27; male OR:0.78, 95 %CI: 0.53,1.15). Future work should more deeply investigate differential physiological impacts of PAH exposure between pregnancies with male and female fetuses, and on varying developmental processes occurring at different points through pregnancy.

Cold start performance of diesel engine at extremely low ambient temperatures and high altitudes: The superiority of premixing diethyl ether

The cold-start performance poses a primary challenge influencing the reliability of diesel engines operating in plateau and low-temperature regions. An experimental investigation was conducted to assess the cold-start performance of diesel engines with premixing diethyl ether (DEE), spanning altitudes from sea level to 4000 m and ambient temperatures of −20 °C and −40 °C. The diesel engine with premixing DEE exhibited successful cold starts at all these test conditions. In comparison, the diesel engine employing intake heating failed to reach idle speed in −40 °C high-altitude conditions. The premixed DEE could generate radicals, accompanied by a minor heat release preceding the injection of diesel, facilitating ignition. Furthermore, the premixed DEE enhanced fuel evaporation and facilitated the formation of combustible mixtures with higher equivalence ratios at low temperatures. Moreover, the fuel film resulting from wall impingement with premixing DEE was thinner than that with intake heating, contributing to decreased incomplete combustion losses. Energy analysis results revealed that the diesel engine employing premixing DEE demonstrated higher indicated thermal efficiency. The cold start assistance by premixing DEE proved to be much more effective, and the test engine could start smoothly under extremely low temperatures of −40 °C and high altitudes up to 4000 m.

Measurement and quantification of methane emissions from residential gas stoves and tankless water heaters in China

Methane is a short-lived and potent greenhouse gas with a rapid warming effect. Gas stoves and water heaters, which are the most widely used domestic gas appliances (over 250 million in China), emit methane because of incomplete combustion and leakage. This study quantified the methane emissions of these two gas appliances at different ages through field measurements and laboratory tests to assess their impact on the climate. Their methane concentrations typically spiked quickly and decayed rapidly during ignition and extinguishment, but were low and stable during the steady-on state. Tankless water heaters emitted 1.69‰ (95% confidence interval: 1.44‰, 2.01‰) of the natural gas consumed, primarily during the on-pulse phase. More than four-fifths of the methane emissions from gas stoves occurred in the steady-on state, and the emission rates were positively correlated with the age of the gas stoves (r2 = 0.79, p < 0.001). Therefore, approximately 28.1 (27.5, 28.6) Gg of methane emissions annually can be attributed to Chinese residential gas appliances, corresponding to a 0.8 Mt. carbon dioxide equivalent over a 100-y scale.