Control-oriented mixing model for Homogeneous Charge Compression Ignition engines

Abstract

A tractable model for in-cylinder fluid motion during the intake stroke is developed with particular attention given to fluid flow through the intake ports. Due to innovations in valve timing strategies for the 4-stroke internal combustion engine, the fluid flow effects of different valve timings must be quantified.An asynchronous valve timing strategy for Homogeneous Charge Compression Ignition engines serves as the motivation for this model development. For the purposes of real-time engine control, the model is not a multi-zone CFD model. Rather, the model divides the cylinder into two zonesa mixed zone and an unmixed zone. The flow is modeled as an intake jet of fluid that determines the rate at which hot exhaust gas is transferred from the unmixed to the mixed zone. The size of the mixed zone at the end of the intake process determines how well the cylinder contents are mixed. The effects of the valve timings on the flow velocity through each intake valve, cylinder pressure, and temperature are also presented.M. J. McCuen is with the Mechanical Engineering Department,

A Control Oriented Charge Mixing and HCCI Combustion Model for Internal Combustion Engines

“…Furthermore, during the gas exchange process described in [1], a first order transfer function was used to approximate the in-cylinder pressure, which led to large errors compared with the actual pressure. In [7] and [8] a two-zone HCCI model was established taking into consideration of unmixed zone during combustion phase. Reference [7] developed a two-zone model based on thermochemistry and chemical kinetics, which ensures better combustion results, but the charge mixing process is not modeled.…”

“…As a result, the size of the unmixed zone cannot be determined in real-time. In [8] a pseudo-velocity method was used to predict the unmixed zone size during intake phase; however, for the negative valve over-lap (NVO) case the simulation error is fairly large between pseudo-velocity and actual intake flow velocity.…”

A Novel Method for CFD Analysis of a Two-Zone Mixing Model for HCCI Engines

“…In a previous work [8], the authors developed a controloriented model that quantified the amount of mixing based on charge inlet velocity for an asynchronous intake valve strategy [9]. This two-zone model was developed to predict how flow velocity would cause the fresh charge to mix with the residual exhaust gas.…”

A Control Oriented SI and HCCI Hybrid Combustion Model for Internal Combustion Engines

“…Also, to have smooth transition between SI and HCCI combustions, accurate intake flow with good mixing is the key. Reference [21] provides a two-zone intake mixing model that describes intake mixing process. References [14] and [15] present an intake strategy entailing opening the intake valves at different timings to improve the flow characteristics and provide better mixing.…”

“…To fully utilize this method, we must have accurate information about the system behavior, particularly, the fluid flow during the mixing process. The developed hybrid combustion model will be integrated with the intake mixing model described in [21] in future. The main goal of mode transition control is to ensure smooth and robust mode transition between SI and HCCI combustions to avoid engine misfire at low load and knocking at mediate load.…”