Alternative Fuels and Emission Control Methods in Compression Ignition Engines

The focus of this doctoral thesis is on the effect of alternative diesel fuels on engine performance, emissions, and emission reduction technologies in diesel engines. The studies focused on normal engine operation, enhanced engine parameters for biofuel use, and on modern aftertreatment technologies. The research included engine experiments, simulations, and optical studies. Especially hydrotreated vegetable oil (HVO) and its blends were studied. For comparison, standard EN590 fulfilling regular diesel and its blends with traditional biodiesel (FAME) were also investigated. FAME and HVO represent different biofuel generations. FAME is a first generation biofuel with typically small-scale production and varying product quality. It consists of oxygen-containing esters not found in pure fossil diesel. Additionally, FAME has lower energy content. The maximum amount of FAME is 7% in standard EN590. HVO is a second generation biofuel with typically large-scale production and high quality. HVO consists of paraffinic hydrocarbons - compounds found also in regular diesel. High proportions of HVO can typically be used in diesel engines without any modifications. The first part of this thesis involves biofuels and their effects on medium-speed diesel engine performance and emissions. The biofuels were evaluated with simulations, and the effects of 100% HVO on engine performance and emissions were investigated with engine experiments. Internal exhaust gas recirculation (iEGR) and Miller timing were studied with regular diesel and HVO. The latter part of the thesis focuses on late post-injections (LPI) with 30% blends of HVO and FAME, used for diesel particulate filter (DPF) regeneration in an off-road diesel engine. During the LPI mode, exhaust gas temperature rise in the diesel oxidation catalyst (DOC), emissions, and oil dilution were investigated. Additionally, the corresponding fuel sprays were investigated in optical engines. With 100% HVO, the compatibility, performance and emissions were first investigated with no engine parameter changes. With Miller timing and iEGR, the high ignitability lead to significant nitrogen oxide (NOx) decrease, with no fuel consumption or particulate matter (PM) emission increase. In contrast to the typical NOx-PM -trade-off, both emissions were lowered. In the LPI studies, no drawbacks were found with 30% HVO blend. 30% FAME blend resulted in worse oil dilution related to LPI's, and increased emissions during the LPI mode. No significant differences in the LPI spray lengths were measured between the fuels. Thus, the differences in the oil dilution were contributed to the distillation characteristics of the fuels.