Experimental evaluation of renewable drop-in fuel blends for compression ignition engines

Abstract: Driven by the need to reduce greenhouse gas emissions while meeting the growing demand for mobility, the transport sector is shifting towards more sustainable and less polluting energy sources. Although vehicle electrification is advancing, it will take decades for electric vehicles to completely replace all current vehicles powered by internal combustion engines. In the meantime, it may be possible to reduce the emissions originating from transport by replacing fossil Diesel fuel with renewable alternatives suitable for use in compression ignition combustion engines. Fuels that can be used in existing engines without modification of hardware or calibration settings are called drop-in fuels. The scientific contribution of this dissertation is an experimental evaluation of potential drop-in fuel blends for the use in a compression ignition engine. The main component of each studied blend was either a long-chain alcohol or poly(oxymethylene) dimethyl ether (OME3-5) blended with hydrotreated vegetable oil and rapeseed methyl ester as well as fossil Diesel fuel in some cases. The performance and emissions of the different fuel blends were investigated experimentally in heavy duty and light duty single cylinder research engines. Some of the long-chain alcohol blends were also investigated in a heavy duty multicylinder engine as well as in optical spray experiments using a high-pressure/high-temperature constant volume chamber. Overall, the obtained results indicate that blends consisting mainly of long-chain alcohols or OME3-5 could replace fossil Diesel fuel in compression ignition engines. Owing to the lower heating value of the fuel blends, the fuel consumption increases slightly. But there is the possibility of improved engine efficiency. Importantly, both long-chain alcohol and OME3-5 blends have the potential to greatly reduce soot emissions. It was concluded from optical spray studies that not only the oxygen content of the fuel but also the increased heat of evaporation influenced the combustion and thus the soot reduction potential. However, light duty engine tests using these blends yielded strongly increased NOx emissions, and the high particle number emissions observed in the heavy duty engine tests could be problematic given the limits on particulate emissions imposed by the most recent emissions standards.