Theoretical Study of Electrically Assisted Two-Stage Turbocharger Boost System Applied to Large-Bore Gas SI ICE

Large-bore gas SI ICEs are supposed to operate under more strict conditions in terms of NOx level and potentially using new generation of fuels (e.g, hydrogen, ammonia) in the near future. Currently, the TA Luft norm is being considered while typical BMEP levels are between 22-28 bars. It is expected that NOx would have to drop significantly (down to 50% or even 20% of the amount based on TA Luft) while engine BMEP is supposed to be increased above 30 bars. The paper is based on 0-D/1-D simulations while using the experience gained from older research projects concerning similar engines. The main goal is to study the influence of different operating conditions (e.g., NOx level, BMEP level, control means, ambient conditions, fuel composition) on both ICE performance and turbocharger operation while comparing classical two-stage system with electrically assisted one – steady state performance is of the main focus while transient one is also considered. Complex optimizations were carried out to achieve optimal solution for every considered operating case. General conclusions are drawn while focusing on the limits of two-stage turbocharging concept.