Design of a high-efficiency, high-BMEP, small car powerplant 841283
An inline, three-cylinder engine was designed to serve as a basis for comparative studies of alternative engine subsystems and features with ultimate application in a research fuel economy concept car. The objective was to provide a fuel-efficient gasoline powerplant with high BMEP, good packageability and a high degree of manufacturing commonality for DI Diesel convertibility. The selected configuration has a square bore/stroke ratio with vertical inline valves offset 5.5 mm from the cylinder centerline.
Two basic chamber configurations were designed, a bowl-in-piston/near-central plug and an open-chamber/dual-plug geometry. Intake ports having high swirl and no swirl were provided for each configuration. High port flow coefficients were achieved, permitting low overall specific head loss in the induction system.
A multi-piece experimental cylinder head structure was conceived, to permit testing of two alternate valvetrains: direct-acting “bucket” tappets and roller-finger followers. This iron/aluminum concept offers an advantageous balance of cost and weight.
For balancing of the primary rocking couple, a balance shaft was provided. A low-friction oil pump design was evaluated and included in the engine program.
Test results to date are summarized, covering induction system optimization, camshaft selection, valvetrain friction studies, and combustion evaluation of the first (bowl-in-piston/swirl port) combustion system alternative. The BIP/helical intake port geometry with optimized, timed sequential fuel injection provided excellent dilute operating capability and thermal efficiency. Unburned hydrocarbon levels were somewhat high.