Lean Homogeneous combustion for SI-Engines

Licentiate thesis, 2015

This thesis is about the application of lean homogeneous combustion in SI engines using a passive SCR after treatment system. By implementing this concept a decrease in fuel consumption and engine out NOx is expected. The data and results are obtained through engine experiments. Under lean conditions the ignition system faces harder conditions, in order to reliably ignite a lean fuel/air mixture an advanced ignition system is necessary. A literature study revealed that among, standard ignition, dual coil ignition, laser ignition, corona ignition and pre-chamber ignition the pre-chamber ignition system was capable of igniting the highest diluted mixture. The corona system however was second best and does not require a modification to the engine. The dual coil ignition system was installed on a multi-cylinder engine. This system uses a standard spark plug but by firing two coils in consecutive order a long duration spark is created. By applying this system and optimizing the timing of the existing adjustable cam shafts for lean conditions, substantial decreases in fuel consumption and NOx were achieved. Another part of this thesis is about the after treatment system. An ammonia formation catalyst produces ammonia under rich engine conditions and stores it. The ammonia in its turn reacts with NOx when the engine operates lean. The ammonia formation catalyst was tested under lab-scale and real engine conditions. It was shown that taken the differences in set-up into account the lab-scale tested catalysts showed good similarities with the engine-scale tests.