Understanding the infiuence of valve timings on controlled autoignition combustion in a four-stroke port fuel injection engine

Abstract

Controlled autoignition (CAI) combustion, also known as homogeneous charge compression ignition (HCCI), was achieved through the negative valve overlap approach by using small- lift camshafts. Three-dimensional multicycle engine simulations were carried out in order better to understand the effects of variable intake valve timings on the gas exchange process, mixing quality, CAI combustion, and pollutant formation in a four-stroke port fuel injection (PFI) gasoline engine. Full engine cycle simulation, including complete gas exchange and combustion processes, was carried out over several cycles in order to obtain the stable cycle for analysis. The combustion models used in the present study are a modified shell ignition model and a laminar and turbulent characteristic time model, which can take high residual gas fraction into account. After the validation of the model against experimental data, investigations of the effects of variable intake valve timing strategies on the CAI combustion process were carried out. These analyses show that the intake valve opening (IVO) and intake valve closing (IVC) timings have a strong infiuence on the gas exchange and mixing processes in the cylinder, which in turn affect the engine performance and emissions. Symmetric IVO timing relative to exhaust valve closing (EVC) timing tends to produce a more stratified mixture, earlier ignition timing, and localized combustion, and hence higher NO x and lower unburned HC and CO emissions, whereas retarded IVO leads to faster mixing, a more homogeneous mixture, and uniform temperature distribution.

Variable Valve Timing Scheduling in a 4-Stroke Internal Combustion Cylinder Utilizing Artificial Neural Networks

“…Caufield S. [6] reported that VVT can decrease fuel consumption in small sparkignition (SI) engines through accurate fluid path simulations. The VVT issue has been shown to be of even more benefit for auto-ignition diesel engines by Cao L. [4], who discussed its effect on gas composition and combination.…”

Analysis of Controlled Auto-Ignition/HCCI Combustion in a Direct Injection Gasoline Engine with Single and Split Fuel Injections

“…Nevertheless, as shown in Fig.1, the prediction of heat release prior to the main combustion with the modified Shell model has been improved over the original model. More detailed model validations under different operating conditions were given in earlier publication (Cao et al, 2005).…”

“…It has been demonstrated that gasoline CAI combustion can be promoted by using either an increased compression ratio (Ryan III et al, 1996;Christensen et al, 1999) or heating of the intake charge (Aoyama et al 1996, Oakley et al 2001, Yang. et al 2002, Zhao. et al 2005.…”

Modeling the Effect of Variable Timing of the Exhaust Valves on SI Engine Emissions for Greener Vehicles

“…Cao et al [9] have investigated the influence of valve timings on controlled auto-ignition (CAI) combustion in a four-stroke engine. The analysis shows that the intake valve opening (IVO) and intake valve closing (IVC) timings have a strong influence on the gas exchange and mixing processes in the cylinder, which in turn affect the engine performance and emissions.…”