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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.

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.

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.

Future fuel formulations including classic refining schemes (hydrotreatment) and synthetic blending stocks like Fischer-Tropsch, oligomerate and high cetane linear ethers were tested for their impact on diesel emissions in various engine conditions (transient and cold operations). CO, HC, Aldehyde, Particulate and PAH emissions are highly sensitive to fuel quality whereas NOx emissions are only slightly modified. Very low level of pollutants is obtained with the Fischer-Tropsch fuel. Oligomerisation fuel induces an increase in CO, HC, aldehyde emissions due to its very low cetane number but presents low emissions of particulates and smoke because of its paraffinic composition. Pentyl ether behaves essentially as a high cetane paraffinic hydrocarbon. The relationships between fuel parameters and emissions were also assessed: CO, HC and aldehyde emissions depend on the cetane number. Particulates, IOF, smoke and PAHs are controlled by aromatic content and density. Density also controlled NOx emissions but with far less variation. Fuel quality can also help to reach a better NOx/particulates trade-off with EGR. Tall-oil methyl ester containing fuel offers a good potential for low emissions because of the beneficial effect of oxygen on particulates.

The purpose of our study was to investigate the effects of TAME and heavier ethers on reformulated gasoline. The research work focused on the comparison of Californian Phase 2 gasoline (CARB), current Finnish reformulated gasoline containing MTBE (RFG1), or MTBE+TAME+heavier ethers (RFG2) with non-oxygenated Eurograde gasoline (EN228). Significant reductions in exhaust emissions were achieved with all reformulated fuels when compared to the Eurograde fuel. For instance, benzene emissions were reduced as much as 40 to 50 % for all cars at two temperatures and the emissions of total toxics were reduced by 14 to 45 % depending on vehicle type and temperature. The lowest 1,3-butadiene emissions were achieved with CARB gasoline. The amount of PAH compounds in the particulate matter from the non-catalyst vehicle was lower with the reformulated fuels than with the Eurograde fuel. The amount of volatile PAH compounds in semivolatile phase of particles seemed to be reduced with reformulated gasoline as well. As gasoline blending components TAME and heavier ethers proved to be as good as MTBE. Additionally they improved the octane number distribution of reformulated gasolines.

Propane is considered to be a viable fuel alternative for low-emission heavy-duty vehicles in Finland. Natural gas and propane have roughly the same potential for reduced exhaust emissions. Since natural gas and propane are both imported fuels in Finland, there is no preference between these two fuels. Propane, however, is much more easy to distribute, refuel and store onboard the vehicle. This is why propane has received more attention than natural gas as an automotive fuel.Work to develop a low-emission propane fueled truck started back in 1988 with engine tests. The first prototype, a 17-ton SISU truck was built in 1990, and was operated until September 1992. This truck was equipped with a 7.4-liter Valmet-engine, a closed-loop controlled IMPCO-fuel system and a three-way catalytic converter (TWC).The experience with this propane fueled truck was good. The driveability was excellent, and both noise level and exhaust emissions were low. The following emission results were obtained in the European 13-mode (ECE R49) emission test with a three-way catalyst aged for 30.000 km: CO 1.8, THC 0.5 and NOx 0.5 g/kWh.Encouraged by these good results the Finnish truck manufacturer Oy Sisu-Auto Ab decided to build a test fleet of seven propane fueled trucks. These trucks were built in late 1992/early 1993. One of these trucks is used for test and demonstration purposes, and six trucks have been delivered to five different operators for various applications like municipal waste collection, distribution work and street maintenance. A surveillance program concerning these trucks is currently under way.In the years 1990-1993 a surveillance project on a propane fueled MAN-citybus was carried out concurrent with the truck operations. This vehicle also uses TWC technology. The surveillance work included both weekly checkups on the fuel system and catalysts. Furthermore, altogether six measurements were carried out on a chassis dynamometer according to a modified ECE R49 procedure.In April 1993 the total accumulated driving distance was some 200.000 km and the bus has worked relatively well, although some minor technical problems have occurred. Judged by the emission test, the original catalyst had lost 50% of its efficiency at 80.000 km. This catalyst was then replaced with a converter from the Finnish company Kemira Oy. With this new catalyst, extremely low emission values were obtained.

Using fast FTIR-technology (Fourier Transform Infra-Red) to complement the normal regulated emission analysis, VTT Energy has performed exhaust emission measurements for several light-duty motor vehicles (passenger cars) representing a variety of current level technologies, mostly employing a three-way catalytic converter. Tests have been performed using standardized test procedures and driving cycles (U.S.EPA and ECE/EEC). Apart from the basic technology of the vehicle, ambient temperature has also been varied. Most of the tests are run at +20 to +22 °C ambient temperature, but additional tests have been carried out at ±0°C, -7 °C and even at -20 °C.Test results suggest that nitrous oxide output varies largely from vehicle to vehicle, and its is also dependent on the ambient temperature. Most significant factor, however, seems to be vehicle mileage, or rather catalyst activity, as already suggested in previous studies. Furthermore, the detailed time resolved analysis supports the theory presented in the literature, that nitrous oxide is formed in a three-way catalytic converter within certain temperature range below the normal operating temperature.