In the Hottel and Broughton equation, the spectral emissivity of soot in flames in the visible wavelength range is characterized by an index α = 1.39, which represents the effect of wavelength on extinction (Hottel and Broughton, 1932). In this study, the spectral specific extinction for diesel soot is examined first by focusing on soot layers sampled on a quartz window from the engine cylinder, and α = 1.38 is obtained. To examine the physics governing the value of α = 1.38, a calculation of spectral extinction is performed using the Rayleigh–Debye–Gans (RDG) theory of soot aggregate scattering with an assumption of constant refractive index. The calculated spectral extinction provides α = 1.31 close to α = 1.38, suggesting that scattering, as well as absorption, contributes largely to the spectral extinction of diesel soot. The attenuation of line-of-sight beam intensity due to out-scattering and the augmentation of the beam intensity as a result of scattering of incoming radiation from other regions are investigated using soot aggregate scattering theory. Based on this approach, a new formula of apparent spectral emissivity εa is proposed, allowing a theoretical explanation of the physical meaning of the KL factor defined in the Hottel and Broughton equation, which has remained vague for many years. Finally the two-colour flame temperature and the KL factor in a production engine are calculated using the new emissivity formula and are compared with those obtained using the conventional emissivity formula. The result shows that the two-colour method using the conventional emissivity formula remains quite useful, and provides values of temperature and KL factor within 1–2 per cent of those obtained with the new emissivity formula.

The real-time estimation of soot mass loading on diesel particulate filters (DPF) is essential to assure perfect and fuel efficient regeneration. Computer models based on the pressure drop across the DPF are usually installed in the engine control unit to estimate the soot mass loading during vehicle driving, but this approach is still subject to uncertainty about the lack of resources available. The aim of this study is to develop a portable instrument that can make real-time measurements of soot mass loading under transient mode for calibrating the models. The instrument is based on the light scattering technique: a laser beam illuminates diesel particles in a small exhaust sample and the intensity of scattered light from soot particles is reduced to soot mass concentration using calibration data obtained under steady engine operating conditions. It is demonstrated that the prototype instrument can measure the temporal variations of cumulative soot mass and filtration efficiency of a diesel particulate filter under a transient mode, and that it has a minimum detectable concentration of 5 mg/m 3 ,which is low enough to detect the particle breakthrough in the DPF. The proposed technique has potential to be applied for on-board diagnostics if the device is downsized.

The use of noninvasive respiratory support is widespread in newborn infants with respiratory distress. As the use of noninvasive respiratory support has increased, so too have the number of modes available. Among these modes, low‐flow nasal cannula and nasal continuous positive airway pressure (NCPAP) have been used for a long time and have known efficacy and safety in newborn infants needing respiratory support. High‐flow nasal cannula (HFNC) has been newly introduced, and its efficacy and safety are currently being investigated. Bilevel nasal continuous positive airway pressure and nasal intermittent positive‐pressure ventilation are often used when NCPAP or HFNC therapy fails. More recently, noninvasive neurally adjusted ventilatory assist and noninvasive high‐frequency oscillatory ventilation have been introduced, and their efficacy and safety are currently under evaluation. Comparison of the efficacy and safety among various modes of noninvasive respiratory support after extubation in preterm infants is helping to clarify the position of each mode. The clarification of the strength and characteristics of each device within the same mode will become important as a future direction of noninvasive respiratory support after extubation in such subjects. However, no research has yet reported on long‐term outcomes in preterm infants receiving noninvasive respiratory support after extubation. Therefore, further research is needed to evaluate the long‐term outcomes.

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