Emulsified fuels in aviation - Water-emulsified diesel fuel in a CI engine for aeronautical applications

Publications

Water-Emulsified Diesel Fuel in a CI Engine Tested for Aeronautical Applications

Publication . Oliveira, Pedro Manuel Pimenta da Silva ; Brójo, Francisco Miguel Ribeiro Proença; Serôdio, Rogério Pedro Fernandes

Water-in-diesel emulsions as an alternative fuel are emerging as a viable option to fight global fossil fuel consumption and emissions restrictions without the need for engine modifications. In an emulsion, two immiscible liquids are mixed with the help of surfactants, where droplets of one liquid are dispersed in a continuous flow. This thesis aims to compare water-emulsified diesel fuel with European commercially available diesel (EN590) when it comes to engine performance and emissions. The tests were performed in a single-cylinder, direct injection diesel engine (Hatz 1B40) using an eddy current dynamometer, an exhaust gas analyser, and an opacimeter. With the objective of testing the engine and the alternative fuels for operating conditions often found in aerial vehicles equipped with diesel engines (same operating principles), the tests were performed for idle settings (simulating the taxiing movement of an aircraft), 100% engine load (simulating the take-off and climbing manoeuvres), 50% engine load (representing the descent, approach, and landing phases), and 75% engine load (representing the cruise component of an aircraft's flight profile) at different engine speeds. Mixtures of EN590 diesel fuel, deionised water, and surfactants were performed in laboratory by mechanical homogenization to obtain the ideal concentrations of the different reagents to be later replicated on a bigger scale using a low-energy mixing method. The emulsions were developed to be optimised at the engine’s operating temperature and heated above the diesel fuel operating temperature to reach similar viscosities during the test procedures. The results suggest that adding water as a dispersed phase in the fuel allows to obtain overall better thermal efficiency and lower emissions of nitrogen oxides and smoke in some conditions when compared to traditional diesel. On the other hand, carbon monoxide, hydrocarbons, and carbon dioxide emissions have increased, possibly due to differences in the injection delay between the fuels. By focusing on performance over stability through the adoption of a hydrophilic emulsion formulation in line with the difficulty of further optimisation in general aviation gasoline engines and the widespread availability of diesel fuel, it can be concluded that water-in-diesel emulsions can be a viable alternative towards the goal of improving fuel consumption rates, lowering emissions, and reducing costs when optimised for specific operating conditions of diesel-powered aerial vehicles.

2025-06-18Doctoral thesis

Open access