Development of a New Light Stratified-Charge DISI Combustion System for a Family of Engines With Upfront CFD Coupling With Thermal and Optical Engine Experiments

A new Light Stratified-Charge Direct Injection (LSC DI) spark ignition combustion system concept was developed at Ford. One of the new features of the LSC DI concept is to use a ‘light’ stratified-charge operation window ranging from the idle operation to low speed and low load. A dual independent variable cam timing (DiVCT) mechanism is used to increase the internal dilution for emissions control and to improve engine thermal efficiency. The LSC DI concept allows a large relaxation in the requirement for the lean after-treatment system, but still enables significant fuel economy gains over the PFI base design, delivering high technology value to the customer. In addition, the reduced stratified-charge window permits a simple, shallow piston bowl design that not only benefits engine wide-open throttle performance, but also reduces design compromises due to compression ratio, DiVCT range and piston bowl shape constraints.

The design, analysis, and experimental testing efforts in developing the combustion system are reported in this paper. A combustion system development methodology was developed and adopted. The methodology features vehicle target cascading, upfront CFD-based design optimization and single-cylinder thermodynamic and optically accessible engine testing for design validation and verification. Application of the methodology allowed a significant reduction of hardware iterations, reducing development time and cost. The LSC DI combustion systems were developed for a family of Ford engines with displacement variants of 0.5, 0.42 and 0.38 liter per cylinder. The systems retained substantial design and component commonality between the DI and PFI variants and among the displacement variants. Significant gains in engine output and fuel economy were demonstrated over the baseline PFI design.