Diesel engines are known for their excellent efficiency and are therefore used in a variety of applications. However, they are also one of the main sources of hazardous emissions such as nitrogen oxides (NO_x) and smoke. Water-in-Diesel Emulsion (WiDE) is an alternative fuel that can possibly reduce some of the pollutant emissions without compromising engine performance. The surfactant formulation for WiDE usually follows the one used in water-in-oil (w/o) emulsions, where low hydrophilic–lipophilic balance (HLB) emulsifiers are preferred for better solubility in the diesel phase and stabilization at storage temperatures. However, by using a hydrophilic blend with a non-ionic surfactant, it is possible to develop an optimized formulation at higher fuel temperatures, which occur during an engine’s operating condition, achieving possibly higher benefits. Across the different speeds, the results for the emulsion show 7.57% mean improvement in specific fuel consumption (SFC), 19.14% mean improvement in thermal efficiency (TE), 5.54% mean reduction in carbon dioxide (CO₂), 20.50% mean reduction in nitric oxide (NO) and 75.19% mean reduction in smoke levels. However, carbon monoxide (CO) and hydrocarbons (HC) emissions were higher, with a mean increase of 81.09% and 93.83%, respectively.

Purpose: The article aims to show the viability of installing a precision-based approach system in Viseu airfield, in Portugal. This work looks to evidence to what extent the implementation of ILS (Instrument Landing System) or GBAS (Ground Based Augmentation System) in the airfield is viable, and which of the two would be the better option for this case, from a technical and economic view and as a way to increase safety levels.Design/methodology/approach: The article analyses the airfield’s evolution over time and forecasts its movements for the future, over a 10-year period, by utilising two different models: multiple linear regression and IATA traffic forecasts. The different types of airfield taxes were also reviewed and their values were estimated for the following years. The equipment’s technical aspects and individual prices were analysed to accurately determine the time needed for the airfield to recover the investment done, allied with an 80% funding European project.Findings: Approach systems are being modernized, and throughout the years more airports and airfields are starting to replace old approach systems for satellite-based new ones. When compared to ILS, GBAS offers more advantages at a technical and economic level, and even for smaller airfields with a low traffic volume, sometimes it can be technically and economically possible to have such systems implemented.Originality/value: Studies about the implementation of new radio aids are usually prepared for big airports by airport operators or ANSPs before major investment projects. However, for most small regional airports in the country, where traffic is not near as big, such studies don’t exist, and for that reason, investigating the possibility of installing such kind of equipment is very important, especially taking into consideration the safety they provide and other benefits that naturally come up with it.

The search for alternative fuels is driven by increasing environmental and health concerns across the globe. Water-in-diesel emulsions (WiDEs) have been explored over the years as a potential fuel for diesel engines to mitigate emissions of greenhouse gases, especially nitrogen oxides and smoke. Researchers have been developing and testing different formulations of emulsified fuels with the common goal of stabilizing the mixture and minimizing pollutant emissions without significantly compromising engine performance. In this work, a novel approach is taken by developing a hydrophilic emulsion formulation optimized for engine operating temperatures, overcoming the storage-related stability issues that most studies focus on. Two different mixtures of WiDE were heated and supplied to a Hatz 1B40 single-cylinder diesel engine. The engine was coupled to an eddy current dynamometer to measure speed, torque, and power values. Emissions of carbon monoxide (CO), carbon dioxide (CO₂), hydrocarbons (HCs), nitric oxide (NO), and oxygen (O₂) were measured by an AVL DiGas 1000 exhaust gas analyzer. Smoke emissions were measured by an AVL DiSmoke 480. This study represents a contribution to the field of alternative fuels for diesel engines by providing experimental evidence that formulating WiDE for operating temperatures can be advantageous and significantly improve thermal efficiency and reduce emissions of NO and smoke at specific engine operating conditions, with a maximum reduction of 46.86% for NO emissions and a maximum reduction of 83.67% for smoke emissions obtained when compared to diesel.