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When switching from regular diesel fuel (sulfur free) to paraffinic hydrotreated vegetable oil (HVO), the changes in fuel chemistry and physical properties will affect emission characteristics in a very positive way. The effects also depend on the technology, after-treatment and sophistication of the engine. To determine the real effects in the case of city buses, 17 typical buses, representing emission classes from Euro II to EEV, were measured with HVO, regular diesel and several blended fuels. The average reduction was 10% for nitrogen oxides (NOx) and 30% for particulate matter (PM). Also some engine tests were performed to demonstrate the potential for additional performance benefits when fuel injection timing was optimized for HVO.

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.

Since 2013, Euro VI heavy-duty on-road vehicles have been on the market in the Europe. Regulated exhaust emissions, including nitrogen oxides and particulate matter, have been cut down to a very low level, independent of fuel (diesel or natural gas). Multiple research papers have shown that the regulated emissions from the Euro VI and US 2010 heavy-duty on-road vehicles tested on chassis dynamometers really deliver emission levels which correspond the type approval requirements, independent of the test cycle used. In-service conformity (ISC), which is included in the Euro VI legislation, requires heavy-duty on-road engine manufacturers to test and prove their engines to comply with the emission legislation during the engine in-use period. The measurements are carried out in the field using PEMS (Portable Emission Measurement System) equipment. This kind of testing, depicting real-world emissions is the final stage to confirm low real-life emissions.