The Effect of Near-Spark-Plug Flow Field on Spark Discharge Characteristics

Advanced spark ignition (SI) engines can operate under lean conditions in order to improve the efficiency and reduce the emissions. Under extensive lean conditions, the ignition and complete combustion of the charge mixture is a challenge, because of the reduced cylinder charge reactivity. The enhancement of the in-cylinder global motion and local turbulence is an effective way to increase the flame velocity, and consequently shorten the combustion duration. The role of air motion in improving air-fuel mixing and combustion has been researched extensively. However, during the ignition process, the excessive charge motion can hinder the spark discharge, the resulting flame kernel formation, and propagation. Therefore, a combined empirical and simulation study is undertaken to elucidate the flow field around the spark gap, and its effect on the spark discharge. The flow field generated by a steady flow of air across the spark gap of a conventional J-type spark plug is studied under ambient conditions. Optical particle image velocimetry (PIV) measurements and computational fluid dynamics (CFD) simulations are performed alongside the high-speed direct imaging. Voltage and current waveforms of the spark channel have been measured, in order to correlate the spark behavior to the local flow velocity. The flow field near the spark gap in an SI engine under motoring conditions is simulated. The results are compared to the empirical current and voltage measurements taken during engine operation. The results show that the turbulence is generated in the wake of the spark plug and flow velocity in the spark gap is higher than the free stream velocity. The optical and electrical measurements show the spark stretching and restrikes increase, and the discharge duration decreases with an increase in flow velocity. Similar behavior is observed during engine operation as well

A Bayesian reanalysis of the Standard versus Accelerated Initiation of Renal-Replacement Therapy in Acute Kidney Injury (STARRT-AKI) trial

Background Timing of initiation of kidney-replacement therapy (KRT) in critically ill patients remains controversial. The Standard versus Accelerated Initiation of Renal-Replacement Therapy in Acute Kidney Injury (STARRT-AKI) trial compared two strategies of KRT initiation (accelerated versus standard) in critically ill patients with acute kidney injury and found neutral results for 90-day all-cause mortality. Probabilistic exploration of the trial endpoints may enable greater understanding of the trial findings. We aimed to perform a reanalysis using a Bayesian framework. Methods We performed a secondary analysis of all 2927 patients randomized in multi-national STARRT-AKI trial, performed at 168 centers in 15 countries. The primary endpoint, 90-day all-cause mortality, was evaluated using hierarchical Bayesian logistic regression. A spectrum of priors includes optimistic, neutral, and pessimistic priors, along with priors informed from earlier clinical trials. Secondary endpoints (KRT-free days and hospital-free days) were assessed using zero–one inflated beta regression. Results The posterior probability of benefit comparing an accelerated versus a standard KRT initiation strategy for the primary endpoint suggested no important difference, regardless of the prior used (absolute difference of 0.13% [95% credible interval [CrI] − 3.30%; 3.40%], − 0.39% [95% CrI − 3.46%; 3.00%], and 0.64% [95% CrI − 2.53%; 3.88%] for neutral, optimistic, and pessimistic priors, respectively). There was a very low probability that the effect size was equal or larger than a consensus-defined minimal clinically important difference. Patients allocated to the accelerated strategy had a lower number of KRT-free days (median absolute difference of − 3.55 days [95% CrI − 6.38; − 0.48]), with a probability that the accelerated strategy was associated with more KRT-free days of 0.008. Hospital-free days were similar between strategies, with the accelerated strategy having a median absolute difference of 0.48 more hospital-free days (95% CrI − 1.87; 2.72) compared with the standard strategy and the probability that the accelerated strategy had more hospital-free days was 0.66. Conclusions In a Bayesian reanalysis of the STARRT-AKI trial, we found very low probability that an accelerated strategy has clinically important benefits compared with the standard strategy. Patients receiving the accelerated strategy probably have fewer days alive and KRT-free. These findings do not support the adoption of an accelerated strategy of KRT initiation