Evaluation of Gasoline PPC in a Multi-cylinder Engine : Capabilities & Challenges

Sammanfattning: Internal combustion engines have been the most used engine design when it comes to vehicle propulsion and transportation. But as the number of vehicles increase, new problems arise as well. Engine emissions such as carbon dioxide that has an effect on a global scale and other harmful emissions that affect on a local scale such as soot and nitrogen oxides are on the rise, forcing the countries to take measures on controlling and reducing them.Gasoline Partially Premixed Combustion (PPC) is an alternative combustion concept that can offer both high indicated efficiency and low exhaust emissions in terms of NOx and soot, compared to conventional diesel combustion (CDC). Previous research has shown that this concept can work well with gasoline fuels of different octane ratings and can be used both in light and heavy duty engines. Although PPC has been tested substantially in research engines, results from engine designs that are closer to production are limited.In this thesis, PPC is evaluated in a multi-cylinder light duty diesel engine. Results show that while it can perform well with both low octane RON75 and higher octane RON90 gasoline, the available load range is limited compared to similar diesel operation. Despite that, efficiency is high, with gross indicated numbers of around 48 %, while brake efficiency reaches up to 41 %. Soot emissions are improved compared to diesel while NOx emissions are in similar numbers. A reason for that is the limited use of EGR compared to previous studies. This was deemed necessary to improve the upper achievable load of the engine.As the use of EGR was a limiting factor, an evaluation of the two possible EGR routes was performed, to investigate the possible gains compared to single route operation. Results show that by combining routes possibility for a 4 % gain in efficiency could be found. Also, low load operation is limited due to the type of combustion and the fuel that is used. A minimum amount of temperature is necessary to promote combustion at lower loads and that is not always possible. By utilizing the glowplugs of a diesel engine, combustion stability can be improved, helping reducing the low load limit.Finally these engine results are evaluated on a simulation model of a hybrid PPC powertrain. Even with an unoptimized diesel engine under PPC conditions, fuel consumption and emissions are comparable to a similar diesel powertrain from a production vehicle, showing that with further development, PPC can become a future possibility that can replace the less efficient SI engine.