Application of Concentric Cam Shafts to a Passenger Car Diesel Engine to Significantly Improve the NO _x /Soot Tradeoff

Trying to improve the modern diesel engine's NO_x/soot tradeoff without giving up fuel economy continues to be a core target for the engine development community. One of the options not yet fully investigated for the diesel is applying variable valve events to the engine breathing process. Already used in some heavy-duty applications, late intake valve closing has long been regarded as a possible strategy for small diesel engines. Single-cylinder tests applying fully variable valve events have demonstrated potential but also raised doubts about VVA benefits on automotive size diesel engines. Full engine testing using realistic valve train technology is seen as key to judging its true performance because it covers not only combustion benefits but also influences like engine pumping on emissions and CO₂.

Different to past publications, this paper focuses on testing a production feasible variable valve train technology on a fully instrumented modern Common Rail diesel engine. Applying a concentric intake cam in the described way to increase valve event duration allows running an over expanding combustion cycle (Miller Cycle). The benefits on the NO_x/soot tradeoff as well as other effects are described.