Advancements in alternative fuels towards sustainable engine combustion

Abstract

This doctoral dissertation focuses on the spray characteristics and engine performance of the alternative fuels for heavy-duty engine application. Alternative fuels like HVO, ethanol, methanol, and ammonia are experimentally tested using optical diagnostics of the spray characterization and compared with conventional EN590 diesel and gasoline. Firstly, spray investigations are conducted in an optical spray chamber using high-speed imaging techniques. The spray characteristics are defined based on the spray tip penetration, opening angle, area, and droplet sizes. The effect of chamber pressure, fuel injection pressure, and fuel heating for flash boiling is studied at real engine-like operating conditions. Secondly, ammonia and hydrogen are utilized in heavy-duty single cylinder research engine for tri-fuel (port-fuel: hydrogen-ammonia mixture, pilot-fuel: diesel) combustion. The engine experiments study the impact of varying port-fuel mixing ratio and pilot amounts on fundamental engine performance parameters.

This dissertation comprises of 4 research publications. Publication 1 includes highspeed shadowgraph imaging to optically investigate the fundamental spray characteristics (i.e., spray geometry and droplet sizes) for HVO, ethanol, and EN590 Diesel at varying fuel injection pressures and chamber densities. Publication 2 and 3 aim to further reduce the carbon foot-print in the internal combustion engines and focus on testing flash boiling for improved spray formation. The effect of superheating is studied for ammonia, ethanol, methanol, and gasoline using schlieren imaging. Publication 4 finally implements hydrogen-ammonia mixture as port-fuel with diesel pilot in a single-cylinder research engine. The effect of changing port-fuel mixture ratio, varying pilot amount, and pilot timings is tested for in-cylinder pressure, heat release rate, indicated thermal efficiency, indicated mean effective pressure, ignition delay time, and other engine performance parameters.

The main research findings from this dissertation are as follows: Publication 1 concludes that ethanol with relatively different fuel properties (i.e., lower viscosity and surface tension) than other tested fuels, shows dissimilar spray geometry. Compared to HVO and EN590 diesel, ethanol sprays propagate at slower rate with wider opening angles and smaller droplet sizes. The results from Publication 2 and 3 indicate unique spray behavior of ammonia at high temperature fuel injection compared to ethanol, methanol, and gasoline. The superheated ammonia sprays experience the most vaporization, realized by lowest penetration and spray areas. The results from Publication 4 show that increasing the hydrogen amount (by Vol. %) in hydrogen-ammonia mixture, the combustion improves, indicating relatively higher cylinder pressure and indicated thermal efficiency. The combustion results show that port-fuel mixture ratio and pilot amount are the main combustion controlling factors, however, pilot injection timing has relatively smaller impact on the concerned combustion.