Combustion Modeling of Spark Assisted Compression Ignition for Experimental Analysis and Engine System Simulations.

[摘要] Advanced combustion strategies provide significant efficiency and emissions benefits compared to conventional spark ignited (SI) combustion, but challenges related to combustion control and load limits have made these technologies difficult to implement in practical systems. Until now, low cost reduced order models necessary for large parametric and multi-cycle studies capable of accurately capturing the full range of combustion modes from homogeneous charge compression ignition (HCCI) and spark-assisted compression ignition (SACI) to SI have not been available. This important computational gap for advanced combustion engine research was the primary motivation for this doctoral work. The outcomes of this study include powerful new tools to evaluate advanced combustion strategies as well as novel methods to incorporate important advanced combustion characteristics into reduced order models. A reduced order thermodynamic model of advanced SACI combustion was first proposed. The model was used with available experimental data and previous high fidelity simulation results to develop a new empirical auto-ignition burn rate model that captures the effects of ignition timing, composition, temperature, pressure, engine speed, stratification and flame propagation.A complete engine model was then developed and incorporated into the commercial simulation software GT-Power. The model included chemical kinetics for low temperature heat release and auto-ignition detection and the empirical burn rate model for post-ignition heat release, as well as a new flame propagation model with improved physical groundings. The calibrated engine model showed good agreement with experimental trends of HCCI, SACI and SI combustion modes.The engine model was then used to assess practical strategies for accessing the advanced combustion regime and improving engine efficiency. The results showed HCCI and SACI provide a pathway for significant efficiency benefits compared to throttled SI, with efficiency improvements between 15-25% across a range of loads from 1-7 bar BMEP. Further efficiency gains appear possible beyond the experimentally observed SACI limit.As a further exercise, the load extension potential of boosted SACI combustion was conceptually investigated using a simple thermodynamic framework incorporating the empirical burn rate model and practical operating constraints. The results indicate boosted SACI can nearly double the maximum engine load compared to naturally aspirated operation.

[发布机构] University of Michigan

[效力级别] Saci

[关键词] Spark Assisted Compression Ignition;Saci;Homogeneous Charge Compression Ignition;Hcci;Spark Ignition;Si;Knock;Advanced Combustion Engines;Combustion Modeling;Engine Simulation;Efficiency;Fuel Economy;Load Extension;Load Expansion;Mechanical Engineering;Engineering;Mechanical Engineering