Abstract
The fuel consumption characteristics of spark ignition engines with direct and port fuel injection forms of fuel delivery have been compared. The comparisons are based on model predictions of engine behaviour, and design and performance parameter values selected to be representative of system type in each case. Stratified and homogeneous charge operating strategies at various air/fuel ratios are considered for direct injection. Lean burn, stoichiometric with exhaust gas recirculation, and, as a baseline, stoichiometric without exhaust gas recirculation are the operating strategies examined for port fuel injection. The calibration maps for mixture air/fuel ratio and exhaust gas recirculation rates have been defined for each case based on limits imposed by gas/fuel ratio and intake air restrictions. Spark timing is assumed to be optimised at MBT for all operating conditions. Brake specific fuel consumption maps are presented. Comparisons of fuel used over the NEDC drive cycle are made for each of the generic engines.