Simulation and Thermodynamic Analysis of High Pressure Lean Burn Engines.

High Pressure Lean Burn (HPLB) engines have the potential to achieve high load with high efficiency and low emissions compared to currently available powertrains. Various HPLB concepts have been experimentally studied in the literature, focusing on the combustion event but often neglecting the techniques required to provide appropriate cylinder boundary conditions. This dissertation investigates the interactions between the combustion event, in this case Homogeneous Charge Compression Ignition (HCCI), and engine processes occurring externally to the cylinder that are critical for HPLB operation. For that reason, multi-cylinder boosted HCCI engines were simulated and analyzed based on energy and exergy flow considerations. The multi-cylinder engine model included several submodels the most critical of which were the HCCI combustion and heat transfer modules. Both of these were evaluated based on different experimental datasets and their capability to simulate wide range operation was assessed. The calibrated models were subsequently used to explore the synergies between boosting, Variable Valve Actuation (VVA), Exhaust Gas Recirculation (EGR) and different compression ratio levels for high load HCCI. It was found that utilizing hot intake air is highly beneficial for boosted operation. Hot air can reduce dependence on residual gas for mixture composition and temperature control; it also allows manipulation of the valve strategy so that boosting performance is optimized. In fact, it enables use of regular high lift valve events for improving engine efficiency and suppressing pressure rise rates. It was found that the combination of advanced boosting systems with VVA strategies offers significant efficiency benefits and renders HCCI technology more accessible for future powertrain applications. Energy and exergy analysis showed that advanced boosting and VVA enhanced dilution levels, suppressed cylinder temperatures and lowered pumping work. The outcome was high levels of thermal and gas exchange efficiencies. These benefits were enough to outweigh drawbacks from increased cylinder irreversibilities and reduced exhaust flow exergy, both resulting from low temperature combustion. Low heat rejection was also explored and was found to be very beneficial for HCCI. Overall, the engine simulation and analysis framework provides a useful tool for exploration and assessment of HPLB engines employing current or future technology.PHDMechanical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/96073/1/smamalis_1.pd