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Over the past decade significant research and development activities have been invested in alternative fuels in order to reduce our dependency on fossil fuel sources and reduce CO2 and local emissions from traffic. One result of these R&D efforts is paraffinic diesel fuels, which can be used with existing vehicle fleets and infrastructures. Paraffinic diesels also have other benefits compared to conventional diesels, for example a very high cetane number and the lack of sulfur and aromatic compounds. These characteristics are beneficial in terms of exhaust gas emissions, something which has been demonstrated in numerous studies. The objective of this study was to develop low-emission combustion technologies for paraffinic renewable diesel in a compression ignition engine, and to study the possible benefits of oxygenated paraffinic diesel. Hydrotreated vegetable oil (HVO), which is a commercial example of paraffinic, renewable diesel, was used with and without oxygenate in comparison with conventional diesel. Exhaust emissions were measured in three steady state conditions. The adjusted engine parameters, such as inlet valve closure and injection timing, injection pressure and amount of exhaust gas recirculation (EGR) were optimized for HVO. The results demonstrate that significant reductions of particulate matter (48-61%), polyaromatic hydrocarbon (75-87%) and NOx (31-54%) emissions can be achieved simultaneously by using HVO with adjusted engine parameters.

The effect of after-treatment on size distribution of heavy duty diesel exhaust is studied with a measurement system sampling directly from the tailpipe. After-treatment systems studied are diesel particulate filter (DPF), oxidation catalyst, and selective catalytic reduction (SCR) technique. Only low level sulfur fuels are used. DPF effectively reduces accumulation mode particles but the formation of ultrafine particles was observed at high load. Oxidation catalyst and SCR system slightly reduce accumulation mode in low load, probably because of the higher volatile fraction of the particles at low load. At high load, ultrafine particles are formed with both catalyst systems resulting most probably from SO3 formation over the oxidation catalyst. With SCR, possible ammonia slip may also contribute to particle formation.

Effect of lubricant on particle emissions was studied using two heavy-duty diesel engines. Both particulate mass and particle number distribution were measured. Differences between lubricants were studied by dosing two percent of each lubricant (diesel engine oil) to diesel fuel. This arrangement was seen necessary to get clear differences between lubricants. The lubricant had a clear effect on particulate mass emissions. Two of the lubricants gave about the same emission as pure diesel fuel. The worst result was more than two times higher than without oil added to the fuel. The lubricants were all diesel engine oils with different base oils/additive package. Lubricant ash content presumably affects particulate mass. However, the difference in ash content between lubricants was no higher than 30%. Therefore, ash content can only partly explain the differences. The combustion characteristics and the sulphur content of the base oil are essential, too. All fuels containing lubricant produced higher number of small particles than pure diesel fuel. The lubricant, which gave the lowest particulate mass result, produced the highest number of particles. The reason might be that when the number of large particles decreases (also particle mass decreases), the small particles cannot agglomerate to the surfaces of larger particles. It is also possible that, for example, oxidation of catalyst could reduce the number of small particles.

In a diesel engine, both physical and chemical properties of the fuel affect exhaust emissions. This study focused on the separation of some physical and chemical effects of the fuel on the NOx emission. The tests were conducted with a bus engine using four diesel fuels with different density and aromatics levels. The measurements were performed using five injection timing settings to screen the effects of changes in actual injection timing. When conventional diesel fuel was replaced by reformulated diesel, NOx was reduced 7-13 %. Changes in the injection timing due to differences in the physical properties accounted only for a minor part (10-25 % relative) of the total reduction of NOx, whereas the greater part of the reduction (75-90 % relative) was due to other reasons, mainly fuel chemical properties.