There is a strong request for heavy-duty gas engines in the Nordic countries for environmental reasons. Therefore, several research projects are going on. This paper describes two of them: a Finnish Sisu truck and a MAN bus, both operating in the city of Espoo, the hometown of the Technical Research Centre.
The truck is equipped with a 7.4 litre Finnish Valmet 612 engine. The development work has included engine tests and tests with a vehicle in laboratory conditions. A 3,3 litre 3-cylinder engine was used for the engine tests. The engine runs on stoichiometric mixture, and has a three-way catalyst based on metal substrate. The engine was run on both methane (compr. ratio 12:1) and propane (compr. ratio 10:1).
Emissions were extremely low with both fuels. In the European 13-mode test 0.4 g CO, 0.1 g HC and 0.1 g NOx per kWh were achieved. Peak thermal efficiency was 35 % for both fuels. Maximum mean effective pressure (BMEP) for a naturally aspirated engine is 9 - 9,5 bar. Turbocharging was tested with propane, and a knock limited BMEP of 12.5 bar was reached.
The truck has been operating on propane since the beginning of 1990. The naturally aspirated 7.4 litre engine gives a maximum power output of 130 kW. Results from tests carried out, both on the road and in laboratory conditions, are given.
The MAN bus is also running on propane and uses stoichiometric air-fuel mixture. The technology is similar to the one used in the city of Vienna. The displacement of the engine is 12 litres, and the maximum power output is 177 kW. The bus has been operating since the beginning of April 1991. It is covered with an extensive follow-up program including exhaust emission measurements. This paper describes these procedures and presents results of the first tests.