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Natural gas and hydrogen enriched natural gas has been tested as fuels together with diesel oil and RME in a single cylinder Scania research engine. The gas was introduced as port injection while the diesel was introduced as early direct injection. Because the gas was premixed with air before combustion and the diesel was injected early in the compression stroke, the engine ran close to HCCI mode. However, a more precise description of the combustion would be PPC (Partially Premixed Combustion) as the diesel oil was not expected to be totally premixed. The experiments revealed that the combustion phasing could successfully be controlled by the amount of diesel oil injected for loads between 3.5 and 7.5 bar IMEPg at 1200 rpm. For a given combustion phasing, the hydrogen was not found to influence the required amount of diesel noticeable. However, a large difference between the RME and diesel oil could be seen by the necessity to inject more RME to obtain the same combustion phasing.

To investigate possibilities for reduction of particulate matter emission from diesel engines, experiments with hydrogen, methane and propane mixed to the inlet air were performed in a Euro 2 Scania diesel engine. The base fuels were marine gas oil (MGO, a diesel oil quality) and biodiesel (80 vol% rape seed methyl ester and 20 vol% soy bean methyl ester). Up to 40 % of the fuel energy was replaced by gas at three different load conditions. The emission of particulate matter (PM) was evaluated through particle mass measurements as well as filter smoke number (FSN) unit. The biodiesel resulted in higher PM emissions at low load, but considerably lower PM emissions at high load compared to MGO. The FSN was much lower for biodiesel than for MGO at all loads. Fumigation was not found to be exclusively advantageous with respect to PM emission.