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Exhaust emissions from heavy-duty diesel vehicles have reduced along with tightening emission regulations. Efficient and clean diesel engines today are supported by high-quality fuels. Furthermore, the exhaust treatment technologies aims to remove the rest of exhaust pollutants. However, it is not sufficient to work only on noxious emissions as focus has al-ready moved to greenhouse gases and decarbonizing the transport sector.We show development steps in exhaust emissions achieved by combining modern heavy-duty engine technologies, clean fuels and exhaust treatment technologies. We also discuss multiple options to produce low-carbon fuels for diesel engines using different raw materials and production processes. For example, paraffinic fuels can be produced from natural gas, biogas, vegetable oils, animal fats, and even from cellulosic feedstock and as electro-fuels.

The NewGas project focuses on characterization of gas combustion emissions. The project studies the effect of the combustion process, fuel, lubricating oil and catalysts on the emission formation. In addition, different emission measurement methods are studied. The earlier developed gas engine research facility was modified to be suitable for studies. Studies with natural gas and propane, as well as with two different lubrication oils and catalysts were done utilizing this facility. The exhaust hydrocarbon (HC) composition was found to be different from propane fuel compared to methane fuel (i.e. natural gas, NG) and no methane was found from the exhaust when using propane as fuel while ethylene, propene and propane were found. The particle mass emissions were low and total particulate matter (PM) resulted to same level with propane and NG fuels. However, remarkable differences were seen in particle number concentrations between fuels. For propane, nanoparticle emissions were significantly smaller than for natural gas. The change of lubricating oil was found to have some effect on the particle emission also.High NOx reductions were observed when using selective catalytic reduction, although the level was not as high with propane fuel as was earlier observed in the case of natural gas fuel. The oxidation catalyst with higher activity was found to decrease also propane emissions and the emissions of particulate matter total mass. However, a catalyst combined with high exhaust temperatures increased nanoparticle number concentrations. In this project, experimental field studies on gas combustion emissions were conducted at biogas and burner combustion facilities. The NOx, CO, methane and formaldehyde concentrations in the biogas engine exhaust were found to be relatively similar to what was measured on the research facility. This indicates that the catalyst studies done at research facility would be relevant also to this real application case utilizing biogas as fuel.The results from the burner studies indicated that the NOx, CO and HC concentrations were all very low when measured downstream of the burner only.

ln-depth measurements of gaseous and particulate emissions were conducted onboard an ocean vessel by researcheis from VTT Technical Research Centre'of Finland Ltd, Finnish Meteorological Institute and Tampere University of Technology. Altogether more than 20 different instruments were used in these onboard measurements. A variety of instruments, MAAP (Multi-angle absorption photometer), Aethalometer, FSN (Filter smoke number), AVL MSS (Micro Soot Sensor) were used to measure black carbon (BC) concentrations. In addition, in-depth characterization of gaseous emissions as well as particulate emissions (concentration, composition, size distribution) and their properties (e g. volatility, secondary aerosol formation potential) of a ship equipped with a modern after treatment system (catalyst + scrubber) was achieved by using state-of-the-art online measurement devices (e.9. SPAMS, ELPI, SMPS, PSM, CPC, FTIR, Horiba PG-250A, Pegasor PPS -sensor, Nephelometer, Thermodenuder, PAM -chamber) and filter collections (AVL Smart Sampler). Fuels during measurements were HFO (0.7Yo Sulphur) and MGO (.0.1% Sulphur). The aim of this measurement campaign was to 1) evaluate suitability of BC instruments for onboard measurements and 2) to conduct in-depth characterization of gaseous and particulate emissions of a modern low emission ship. A special focus was on BC emissions as the international maritime organisation (lMO) limit is anticipated for BC emitted by ships. Measurements were successful and large amount of data about the ship emissions was collected. The particulate and gaseous emissions of ship were very low, as expected for a modern ship. The goal is to publish results in the scientific journals and as conference publications. ln addition information for authorities and IMO about the suitability of BC measurement methods for onboard BC measurements will be provided.

The CENGE project focuses on characterization of gas engine emissions comprehensively and studies the effect of different techniques on the emission formation. In addition different emission measurement methods are studied. To mimic the emission matrix of 4 stroke medium speed gas engine a new test facility is developed. The project is based on experiments conducted in engine laboratory and on power plant. Measurements of natural gas engine exhaust gas emissions resulted to rather high levels of hydrocarbons and carbon monoxide. The main HC component was methane while ethane, propane and ethylene were also found. These components are found also in the natural gas. The NOx and particle mass emissions were low. However, significant amount of nanoparticleswas found in the exhaust.Several different catalysts were studied, including SCRs, oxidation catalysts, a methane oxidation catalyst (still under development) and combinations of those. High NOx reductions were observed when using selective catalytic reduction, although a clear decrease in the NOx reduction was recorded at higher temperatures. The relatively fresh methane oxidation catalyst was found to reach reductions greater than 50% when the exhaust temperature and the catalyst size were sufficient. At all measurement campaigns catalysts were found to decrease the emissions of particulate matter total mass. However, nanoparticle numberconcentrations were increased by a catalyst combined with high exhaust temperatures. In one experiment, the behaviour was connected to sulphur compounds while in the other, by contrast, the increase in particle emission at higher catalyst temperatures was due to an increase in organics. The engine out particle emissions between these measurements differed also, one explanation to this being the change of lubricating oil. In addition to primary particle emissions, secondary emission was studied utilizing a potential aerosol mass (PAM) chamber: the particle mass measured downstream the PAM chamber, was found to be 6-170 times as high as the mass of the emitted primary exhaust particles.The fraction of organics was approximately half of the produced secondary aerosol mass.

This domestic project, Future Combustion Technology for Synthetic and Renewable Fuels in Compression Ignition Engines (ReFuel), was part of a Collaborative Task "Future Combustion Technology for Synthetic and Renewable Fuels in Transport" of International Energy Agency (IEA) Combustion Agreement. This international Collaborative Task is coordinated by Finland. The three-year (2009-2011) project was a joint research project with Aalto University (Aalto), Tampere University of Technology (TUT), Technical Research Centre of Finland (VTT) and Åbo Akademi University (ÅAU). The project was funded by TEKES, Wärtsilä Oyj, Neste Oil Oyj, Agco Sisu Power, Aker Arctic Technology Oy and the research partners listed above.Modern renewable diesel fuels have excellent physical and chemical properties, in comparison to traditional crude oil based fuels. Purely paraffinic fuels do not contain aromatic compounds and they are totally sulphur free. Hydrotreated Vegetable Oil (HVO) was studied as an example of paraffinic high cetane number (CN) diesel fuels.HVO has no storage and low temperature problems like the fatty acid methyl esters (FAMEs) have. The combustion properties are better than those of crude oil based fuels and FAME, because they have very high cetane numbers and contain no polyaromatic hydrocarbons (PAH). With low HVO density, viscosity and distillation temperatures, these advantageous properties allow far more advanced combustion strategies, such as very high exhaust gas recirculation (EGR) rates or extreme Miller timings, than has been possible with current fossil fuels. The implementation of these advanced combustion technologies, together with the novel renewable diesel fuel, brought significant nitrogen oxides (NOx), particulate matter (PM) emission reductions with no efficiency losses.The objective of ReFuel project was to develop new extremely low emission combustion technologies for new renewable fuels in compression ignition engines. The target was to decrease emissions at least by 70%. The scope was to utilize the physical and chemical properties of the renewable fuels that differ from properties of the traditional crude oil based fuels and to develop optimum combustion technologies for them. The project focused firstly, on paraffinic high cetane number fuels i.e. hydrotreated vegetable oil fuel as a typical representative of this kind of fuel and secondly, on fuels with high content of oxygenates. This was implemented by blending oxygenate to HVO fuel.

The emission legislation is a driving force of vehicle industry in terms of reducing exhaust gas emissions. To meet the tightening emission limits there is need to develop engine technology to decrease engine out emissions as well as a need to use different type of exhaust gas aftertreatment devices. Particulate emissions are one of the main concerns especially with diesel powered vehicles. At the same time with the tightening emission legislation there is a clear demand on decreasing greenhouse gas emissions of traffic. The use of renewable fuels instead of fossil fuels is one possible way to reduce traffic related CO2 emissions. At VTT's engine and vehicle laboratory there have been several projects and research programs to define the emissions of heavy duty vehicles using different aftertreatment systems and alternative fuels and the some of the main findings about the particulate emissions will be presented.

Helsinki Region Transport, Neste Oil, Proventia Emission Control, VTT Technical Research Centre of Finland and Aalto University carried out a 3.5 year PPP venture "OPTIBIO" to demonstrate the use of paraffinic renewable diesel (hydrotreated vegetable oil HVO) in city buses. The project cooperated with the bus manufacturer Scania. The fleet test in Metropolitan Helsinki, involving some 300 buses at four bus operators, was the largest one in the world to demonstrate this new fuel. The fuels were a 30 % HVO blend and 100 % HVO. The field test was supplemented by a comprehensive in-laboratory research programme on fuel effects on exhaust emissions and low-temperature operability. All in all, the vehicles accumulated some 50 million kilometres between September 2007 and December 2010, of which some 1.5 million kilometres on 100 % HVO. Average distance per vehicle was some 170,000 km. The amounts of fuel used were about 22 million litres of blended fuel and 1 million litres of neat HVO. The project confirmed that HVO actually works as a drop-in fuel, meaning that HVO can replace diesel fuel 100 % without any modifications to the refuelling system or to the vehicles, without causing any operational problems. The emission testing, both the screening and the follow-up measurements, demonstrated significant and permanent emission benefits. Based on the findings of the OPTIBIO project, Scania has approved the use of 100 % HVO (NExBTL) in its city and intercity buses with DC9 engines. After the demonstration phase, the markets will determine the future of high concentration HVO fuels in Finland. Low-level blending is already used commercially to fulfil the general biofuels obligation.

This study presents emission results measured with renewable and synthetic diesel fuels. Three engines and five city buses were studied. The efficiency of diesel oxidation catalyst combined to particle oxidation catalyst (POCr) was measured with two engines. The studied diesel fuels were EN590, FAME, HVO and GTL. In most cases all regulated emissions decreased with HVO and GTL fuels compared to conventional EN590 diesel fuel. With FAME, the NOx emissions were higher compared to EN590, but other emissions were reduced. Alternative fuels had a positive effect on emissions, which are considered harmful to human health.

The report at hand is documentation of the results from VTT on emissions and performance of heavy-duty engines and vehicles using hydrotreated vegetable oil, ester-type biodiesel, GTL diesel, CNG and selected blends in reference to fossil diesel fuel. Report combines result form three different projects which are closely related to each other. Three engines and five city buses were used for the study. In addition, the efficiency of diesel oxidation catalyst combined to particle oxidation catalyst (POCr) was measured with two engines and a long term test was performed with diesel oxidation catalyst using EN590 and RME fuels. Extensive exhaust gas emission measurements were carried out over the measurement periods. In addition to regulated emissions (HC, CO, NO, PM) a number of unregulated emission compounds were measured and analyzed e.g. CO2, aldehydes, particle size distribution and total number, polyaromatic hydrocarbons, mutagenicity of particles and several gaseous compounds with FTIR. Results show that in most cases all regulated emissions decrease with HVO, GTL and RME fuels compared to conventional EN590 diesel fuel. Alternative fuels have also a positive effect on emissions, which are considered harmful to human health. The selected results of the whole study are presented in this paper.