Towards sustainable heavy-duty transportation : Combustion and emissions using renewable fuels in a compression ignition engine

Abstract: Transportation should become sustainable and available to everyone. Currently, transportation accounts for approx. one sixth of greenhouse gas (GHG) emissions globally, and heavy-duty trucks are responsible for almost 30% of that. When fossil diesel fuel is burned in a compression ignition engine, known as a diesel engine, it releases large amounts of CO2, a GHG, into the air. GHGs confine heat in our atmosphere, causing global warming. Furthermore, the emissions are polluting air locally, having negative impact on human health and nature, but also some are adding to the global warming effects. Renewable diesel-like fuels, RME (rapeseed oil methyl ester) and HVO (hydrotreated vegetable oil), and light renewable or less carbon-intense alcohols, methanol and ethanol, as well as blended fuel E85 (ethanol and gasoline), can be used to reduce net CO2 emissions, particulate matter (PM) and gaseous pollutants from the engine. They are available on the market and can be fed to diesel engines without major hardware modifications or by using the available technology. The aim of this PhD thesis was to investigate the effect of replacing fossil diesel fuel with renewable fuels, on the performance and local exhaust emissions of a heavy-duty diesel engine.In experimental studies, particle size distributions in the exhaust were compared to those of fossil diesel. The origin of PM from these less-sooting fuels was studied. The compositions of organic aerosol (OA) and secondary organic aerosol (SOA) from HVO, RME and fossil diesel were analyzed, and the effect of a diesel oxidation catalyst (DOC) was evaluated. Formation of SOA in the atmosphere was simulated by aging emissions in an oxidation flow reactor. The nanostructure of the soot when operating on RME, diesel, methanol or ethanol was studied. Finally, the viability of using E85 fuel in a production truck engine was tested.Ethanol and methanol proved to be nearly non-sooting fuels, with the nanoparticles in the exhaust originating primarily from the lubrication oil. The engine performed well with E85 fuel, with almost all raw emissions below the current legislated levels for one operation setting.PM emissions were significantly lower when fossil diesel was replaced with HVO or RME. The chemical composition of OA was likely dominated by lubrication oil for all three diesel-like fuels. RME reduced both the OA emissions and changed the composition with evidence for minor fuel contributions in the mass spectra. The unregulated nanoparticles of size between 5 nm and 23 nm, which are also thought to originate from the lubrication oil, were emitted in high numbers as nucleation mode. RME and diesel branched soot agglomerates were composed of several tens to hundreds of primary particles, and diesel soot also contained fly ashes from burned engine lubrication oil. SOA formation was substantially lower for RME compared to fossil diesel and HVO. The DOC strongly reduced primary organic emissions in both the gas (hydrocarbons) and particle phase (OA), and only 12 marginally affected OA composition. The DOC was also effective in reducing SOA formation upon atmospheric aging.In order to defossilize transportation, all available technology and research efforts need to get united. When it comes to the heavy-duty sector, the most straightforward solution would be to replace fossil diesel fuel with a diesel-like fuel of non-fossil origin, beginning with the existing vehicle fleets. The use of HVO, RME and light alcohols would have a positive impact on an overall PM reduction.