This paper presents the first results of an experimental study into a hybrid combustion concept for next-generation heavy-duty diesel engines. In this hybrid concept, at low load operating conditions, the engine is run in Pre-mixed Charge Compression Ignition (PCCI) mode, whereas at high load conventional CI combustion is applied. This study was done with standard diesel fuel on a flexible multi-cylinder heavy-duty test platform. This platform is based on a 12.9 liter, 390 kW heavy-duty diesel engine that is equipped with a combination of a supercharger, a two-stage turbocharging system and low-pressure and high-pressure EGR circuitry. Furthermore, Variable Valve Actuation (VVA) hardware is installed to have sufficient control authority. Dedicated pistons, injector nozzles and VVA cam were selected to enable PCCI combustion for a late DI injection strategy, free of wall-wetting problems. The decision to use a multi-cylinder configuration instead of a single cylinder research engine was taken because this allows to assess the impact of limitations in operating range of current turbocharger equipment and that of cylinder interaction. It also allowed to assess control issues relevant for future production engines. First results are shown for four low load ESC operating points. Injection timing, EGR rate and effective compression ratio are varied to find suitable PCCI operating conditions with this equipment. The effect of these control parameters on combustion phasing, heat release, emissions (NO_x, HC, CO, smoke), and fuel consumption is presented. Similar trade-offs are determined for conventional CI combustion at higher loads. From the experimental results, it is concluded that PCCI combustion is successfully realized up to 25% load, corresponding to 5.6 bar BMEP. Further optimization of TC matching and combustion is needed to improve PCCI fuel efficiency and especially high load CI operation.

Presenter
Erik Doosje, TNO Science & Industry