THE EFFECTS OF ENGINE VARIABLES AND EXHAUST GAS RECIRCULATION ON EMISSIONS, FUEL ECONOMY, AND KNOCK - PART III 770192

Steady-state engine mapping data were obtained from a 400 CID V-8 spark-ignition engine at compression ratios of 8.0 and 9.3:1 to determine the effect of compression ratio on fuel consumption and octane number requirement at various exhaust emission levels. The results indicate that increasing compression ratio from 8.0 to 9.3 decreases BSFC without changing BSNO_x emissions, but increases BSHC emissions. Additionally, when BSHC emissions are maintained at the constant levels considered in this study, the minimum BSFC decreases with increasing compression ratio and is obtained at A/F ratios of 16 to 18:1. Since this trend of decreased fuel consumption with increasing compression ratio at fixed HC and NO_x emission levels is the opposite of that indicated by earlier studies using a single-cylinder RDH engine, some possible explanations for these differences are presented. In actual vehicle operation, octane requirements would generally increase with increasing compression ratio. Other studies, however, have shown that the energy savings due to improvement in engine efficiency with increased compression ratio may be more than offset by refinery losses incurred in producing higher octane fuels.