Evaluation of Direct-Injection Burn Rates for Future Mixing-Controlled Combustion Engines

Autoren

Chad Koci, Dr. Advitya Patyal, Caterpillar Inc., Mossville, IL, USA

Zusammenfassung

Current and future mixing-controlled combustion engines need to continue down the path of increased efficiency, power density, and reduced emissions. The origin of the engine’s efficiency stems from the chemical heat release and burn rate during the expansion phase of the cycle. The present work evaluates burn rates generated from direct-injection combustion systems with respect to Gross Indicated Efficiency, Brake Indicated Efficiency, and engine system boundaries. Tens of thousands of 1D engine cycle simulations performed in DYNASTY™, Caterpillar’s dynamic and thermo-hydraulic systems simulation code, explored both theoretical and realistic burn rates using Wiebe functions and predictive mixing-controlled combustion models, respectively. It was found that when limited by peak cylinder pressure constraints, increasing the burn rate beyond a certain level is detrimental. The specific engine load influences when
the cycle is constrained by peak cylinder pressure, and therefore what qualities of the burn rate are desirable. Efficiency was insensitive to the shape of the burn rate when the burn duration was sufficiently short (<30 CAD). Many combinations of fuel injector flow rate and injection pressure were found to produce suitably fast burn rates. However, efficiency improvements were generated by injection mass flow rates up to 2-3 times today’s levels and additionally were driven by high BMEP requirements (20-40 bar). 3D CFD simulations conducted in CONVERGE™ link the 1D predictions of direct-injection burn rates to the specific injection and geometry design aspects of a mixing-controlled combustion system. A discussion and comparison of the 3D CFD with the 1D burn rate simulation direction concludes with combustion system recommendations.

Mitglieder-Login