Experimental Investigation on the Effects of Design and Control Factors on the Performance and Emissions Characteristics of a Boosted GDI Engine Using Taguchi Method

Abstract

Mixture formation and combustion dynamics are the primary contributors to the performance and emission characteristics of direct-injected spark ignition (SI) engines. This requires assessing the benefits and tradeoffs of the design and control factors that influence mixing and the subsequent combustion event. In this study, Taguchi's L18 orthogonal array design of experiment (DoE) methodology has been applied to assess contributions and tradeoffs of varied compression ratio, piston bowl design, intake port tumble design, injector spray pattern, injection timing, injection pressure, exhaust gas recirculation (EGR) rate, and intake valve closing timing in a single-cylinder boosted gasoline direct injection (GDI) SI engine. This multiparameter study has been carried out across three speed-load conditions representative of typical automotive application operating ranges. Analysis of signal-to-noise (S/N) ratio responses yielded an understanding of positive and negative contributions of each control factor at each speed-load condition, and the predictions obtained using the Taguchi DoE approach were validated using confirmation tests with the chosen settings. Analysis of variance (ANOVA) on S/N responses was performed to identify the relative significance of the design and control factors on chosen response factors that included engine output, combustion stability, and emissions. For the specified ranges of each factor tested, compression ratio, intake port design, injection timing, EGR rate, and intake valve closing (IVC) timing were identified as significant contributors to the chosen response parameters. The Taguchi method was found to be an effective technique to perform a multiparameter investigation that could identify the best trade-off of design and control factors to meet a given performance target.