Lean Limit Expansion up to Lambda 2 by Multi-Point Microwave Discharge Igniter

The main challenge to run the engine at ultra-lean or high EGR conditions depends on robust ignition of the mixture i.e. generation of a repeatable and robust ignition kernel to subsequently ignite the fuel-air mixture. We had developed microwave enhanced ignition system in which regular spark is augmented by microwaves which generates a bigger size plasma where. large pool of active radicals effectively increased the initial flame speed, engine efficiency, extended the lean limit and resultant decrease in COV of IMEP. Recently, we developed another plasma-based ignition device named Microwave Discharge Igniter (MDI) which works on the principle of microwave resonation within a cavity. MDI is a compact 4.5 mm plug with a quarter coaxial cavity resonator built into its structures. It receives the microwave (MW) pulse signal at 2.45 GHz from a semiconductor-based MW generator which can be controlled to produce very precise pulse characteristics such as pulse width, pulse number and pulse frequency, with time resolution down to 0.1 μs. The MDI has been shown to have very good combustion performance, including dilution and lean limit extensions. An igniter for gasoline engine also needs to be robust. Hence, the MDI was put under stress and endurance tests. The tests were carried out inside a constant volume chamber at non-reactive condition up to 0.5 MPa. The MDI was controlled to discharge continuously for more than 20 million times, 124-hour straight, mimicking the standard lifetime of 20,000 km highway driving. The compact size of the igniter means that multi-point ignition inside the combustion chamber is possible. In this study, a 3-point MDI plug with M12 size was developed and tested inside a practical commercially available multi-cylinder engine to evaluate the performance of multi-point ignition. The lean limit was compared with a standard spark ignition system at 1460 rpm engine speed and 20 Nm engine torque condition. As expected, 2-point ignition performed better than single-point, reaching the air-fuel ratio of 31 (approximately Lambda, λ = 2.1) in cylinders #1 and #3. However, the variance in IMEP of cylinder #2 was higher than that of cylinder #1 and #3 at the same airfuel ratio for both spark ignition and multi-point MDI. This is caused by cylinder difference of combustion due to the mounting platform constraint imposed on the intake manifolds. Even though the engine used for this study was not optimally designed for higher lean limits at the chosen conditions of this study, the multi-point MDI demonstrated a better load and emission performance tests maintaining exhaust gas temperatures below 300°C and achieving single digit ppm of NO compound emission

Epidemiologic trends and distributions of imported infectious diseases among travelers to Japan before and during the COVID-19 pandemic, 2016 to 2021: a descriptive study

BACKGROUND: Little is known about the trends of imported infectious diseases among travelers to non-endemic countries during the COVID-19 pandemic. This article aimed to describe those among travelers to Japan. METHODS: This is a descriptive study based on national surveillance data. Imported infectious disease cases were defined as those with a reported overseas source of infection among 15 diseases pre-selected based on the probability and impact of importation. The number of notified cases from April 2016 to March 2021 were described by disease and time of diagnosis. The relative ratio and absolute difference in case counts-both by number and per arrival-were calculated by disease comparing those from the pandemic period (April 2020-March 2021) to the pre-pandemic period (April 2016-March 2020). RESULTS: A total of 3524 imported infectious disease cases were diagnosed during the study period, including 3439 cases before and 85 cases during the pandemic. The proportionate distribution of diseases changed but notification counts of all 15 diseases decreased during the pandemic. Accounting for arrivals, however, seven diseases showed a two-fold or greater increase, with a notable absolute increase per million arrivals for amebiasis (60.1; 95%CI, 41.5-78.7), malaria (21.7; 10.5-33.0), and typhoid fever (9.3; 1.9-16.8). CONCLUSION: The epidemiology of imported infectious diseases changed during the pandemic. While the number of imported infectious disease cases decreased, the number of cases per arrivals increased considerably both in relative and absolute terms for several diseases of public health and clinical importance