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Hydrotreated vegetable oil (HVO) named NExBTL is a 2nd generation renewable diesel fuel made by a refinery-based process converting vegetable oils to paraffins. Also animal fats are suitable for feedstocks. Properties of this non-ester type biobased fuel are very similar to GTL. It contains no sulfur, oxygen, nitrogen or aromatics. Cetane number is very high (∼90). Cloud point can be adjusted by severity of the process from -5 to -30°C, heating value is similar to diesel fuel, storage stability is good, and water solubility is low. Emissions of two heavy duty engines and two city buses are presented with HVO and sulfur free EN 590 diesel fuel. The effect of HVO on regulated emissions compared to EN 590 fuel was: NOx -7 % ⋯ -14 % PM -28 % ⋯ -46 % CO -5 % ⋯ -78 % HC 0 % ⋯ -48 % Aldehydes, PAHs, mutagenicity and particulate size were also measured.

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.