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 NO_x 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 bar. It is expected that NO_x will have to drop significantly (down to 20% or even below 10% of the amount based on TA Luft) while engine BMEP is supposed to be increased above 30 bar. 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., NO_x level, BMEP level, control means, ambient conditions) on both ICE performance and turbocharger operation while comparing classical 2-stage system with 2 electrically assisted ones (e-turbo, e-booster) – 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. The main conclusion is that the potential to improve BSFC when e-assisted turbocharging is applied under the steady-state operation is low and it makes sense only under specific conditions. On the other hand, e-assistance significantly improves engine transient response.