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,

Due to the need for clean and efficient automobile propulsion systems, this paper models an important process in the enabling of homogeneous charge compression ignition (HCCI) engines. The need for a deep understanding of charge-residual mixing in residual-affected HCCI engines requires a model of the chemical composition during the mixing process. In this paper, a chemical composition model is developed specifically for a two-zone mixing model to account for important phenomena such as the presence of unburned fuel in the residual exhaust gas. The model is developed as a control-oriented model that can be used for real-time decision making and control. This paper develops the composition model for the major species present, and also presents the method that would be used to include other minor species. The model is simulated for variations in residual gas fraction equivalence ratio, a misfire situation, and its effects on air/fuel ratio.

Increasing need for clean and efficient energy conversion devices in the automotive sector has pushed technologies such as homogeneous charge compression ignition (HCCI) to the forefront of research. While it offers a number of major advantages in terms of efficiency and emissions, HCCI has significant challenges to overcome before it can be used in a production setting. Among those challenges is the need to control the start of combustion, and one method for doing that is to use variable valve timing to utilize hot, residual exhaust gas. Critical to these residual-affected methods is the role of mixing on the thermodynamic state. This work presents a method for validating a control-oriented two-zone mixing model for HCCI using CFD software. A method of discretizing, extracting, and analyzing the results of the CFD simulation is described, and it is compared with the two-zone model. There is strong correlation, but there is also evidence that the twozone model needs to be further developed to fully capture the dynamics of mixing.