Investigation of biofuelled combustion and their performance optimisation strategies for internal combustion engines

Abstract

The increasing use of biofuels to replace fossil fuels as well as more stringent emissions regulations for internal combustion engines cause a challenge for the engine manufacturer to build engines that can cope with a large range of fuel properties, but still offer low fuel consumption and very low exhaust emissions. In this work a heavy-duty diesel engine test bed has been built including the fuel and emission analysis equipment suitable for a wide range of biofuels. Also a constant volume spray vessel has been commissioned to optically investigate the macroscopic spray characteristics of different fuels. This vessel was built with the potential investigation of fuel combustion in the future. Four different biofuels, soybean oil methyl ester (SME), palm oil methyl ester (PME), used cooking oil methyl ester (UCOME) and hydrotreated vegetable oil (HVO) in blends of B10, B20, B50 and B100 have been tested, as they are potential candidates to replace mineral diesel in larger scales. The main aim of this project was to investigate the spray and combustion characteristics of various biofuels, their impact on exhaust emissions and performance and the potential optimisation of the control strategy in a heavy-duty Euro V diesel engine. The engine tests revealed that for all biofuels the nitric oxide (NOx) emissions increased compared to mineral diesel (B0), while particulate number (PN), carbon monoxide (CO) and total hydrocarbon (THC) were significantly reduced. The fuel consumption changed according to the heating value and with the three fatty acid methyl esters (FAME) full power was not reached. The macroscopic spray tests showed that lower density fuels, such as HVO, have slower penetration speeds, but wider spray cone angle resulting in better fuel-air mixing conditions. As the engine fuel injection is based on a volumetric injection the heating value and fuel density are mainly influencing the spray characteristics on the engine. In the last part the engine power has been successfully restored for all biofuels and the exhaust emissions have been reduced below the B0 benchmark limits by applying a new engine control strategy showing that the use of neat biofuels can be used on heavy-duty diesel engines without any modifications to the engine hardware and still passing the current emission regulations.