Estimates of the air-fuel ratio at the time of ignition in a pre-chamber using a narrow throat geometry

The benefits of pre-chamber combustion (PCC), such as improved engine efficiency and reduced NOx emissions, are primarily observed when operating at lean conditions with an active pre-chamber, where auxiliary fuel is supplied directly to the pre-chamber. Estimating the pre-chamber excess air ratio (λ) is important in the active pre-chamber concept to gain insights into the pre-chamber combustion phenomenon. Experimental investigations were performed using a narrow-throat pre-chamber at global-λ 1.6, 1.8, and 2.0. The fraction of fuel energy injected in the pre-chamber over the total fuel energy was fixed at 3%, 7%, and 13% for each global-λ. The mixture formation process inside the pre-chamber is first simulated using the 1-D simulation software GT-Power to analyze the pre-chamber λ at the ignition timing. However, the 1-D results were unable to reproduce the experimental observations on the pre-chamber pressure buildup accurately. Upon simulating the same conditions using the 3-D CFD software CONVERGE, the pre-chamber λ estimated from the CFD model is well-correlated to the experimental data. The CFD results indicate that the amount of fuel trapped in the pre-chamber at the inlet valve closing timing is over-predicted by the 1-D simulations. A correlation between the injected and the trapped fuel in the pre-chamber is proposed by theoretical scavenging models and applied to the 1-D simulation results to improve pre-chamber λ prediction accuracy.

Lipidomic analysis of adipose-derived extracellular vesicles reveals their potential as lipid mediators of obesity-associated metabolic complications

Adipose extracellular vesicles (AdEV) transport lipids that could participate to the development of obesity-related metabolic dysfunctions. This study aimed to define mice AdEV lipid signature in either healthy or obesity context by a targeted LC-MS/MS approach. Distinct clustering of AdEV and visceral adipose tissue (VAT) lipidomes by principal component analysis reveals specific lipid composition of AdEV compared to source VAT. Comprehensive analysis identifies enrichment of ceramides and phosphatidylglycerols in AdEV compared to VAT in lean conditions. Lipid subspecies commonly enriched in AdEV highlight specific AdEV-lipid sorting. Obesity impacts AdEV lipidome, driving triacylglycerols and sphingomyelins enrichment in obese versus lean conditions. Obese mice AdEV also display elevated phosphatidylglycerols and acid arachidonic subspecies contents highlighting novel biomarkers and/or mediators of metabolic dysfunctions. Our study identifies specific lipid-fingerprints for plasma, VAT and AdEV that are informative of the metabolic status and underline the signaling capacity of lipids transported by AdEV in obesity-associated complications.

Benefits and Challenges Associated with the Implementation of Lean in Transportation Agencies

The highway construction industry constantly looks to increase productivity while public transportation agencies face challenges of shrinking budgets and staff numbers, even as the work continues to increase in size and demand. As a paradigm to maximize value and minimize waste with the resources available, Lean offers promise to enhance productivity, quality, and service. This study investigates the implementation of Lean by evaluating Lean conditions, practices, benefits, and challenges as expressed by U.S. and UK public transportation highway agencies as well as comparing the implementation of Lean between these agencies. Using a comprehensive literature review and formal interviews with six state departments of transportation along with Highways England from the UK, the findings show that Lean is intended to make process improvements to boost products and services to consumers. By creating a culture of continuous improvement, transportation agencies can improve their processes and increase their efficiencies and performance. Conversely, transportation agencies struggle to educate their employees and stakeholders in their understanding and practices of Lean, which causes confusion and ineffectiveness. Comparing the U.S. and UK transportation agencies, the approach to Lean implementation differs from a top-down approach for U.S. agencies to a bottom-up approach for Highways England. Furthermore, Highways England has an established tool for measuring Lean while development of quantifiable Lean measures is in its infancy in U.S. agencies. Overall, while the sample is limited, this exploratory study provides information for transportation agencies to use in consideration of implementing Lean.