Modeling and experimental studies of a large-bore natural gas engine operating on homogeneous charge compression ignition

The Homogeneous Charge Compression Ignition (HCCI) engine is under widespread investigation due to its potential to lower NOx and particulate emissions while maintaining high thermal efficiency. Nevertheless, HCCI operation presents several challenges as the combustion event is very unstable under certain conditions. Furthermore, the HCCI combustion mode typically suffers from reduced power density and high-unburned hydrocarbon emissions (∼15 g/kW-hr).; Accurate and yet computationally expedient HCCI engine models are necessary to evaluate approaches and guide experiments for improving power density, pollutant emissions, and controllability. Therefore, the objectives of this work are twofold: (1) develop a fundamentally-based quasi-dimensional model that can be used to evaluate HCCI engine performance and emissions tradeoffs over a range of conditions and configurations; (2) experimentally characterize HCCI performance, emissions, and gas-side boundary conditions under large-bore, turbo-charged configurations.; In this study, natural gas was used as the fuel, primarily because its characteristics complement the HCCI process. A full-cycle simulation was developed to model the HCCI engine process under turbo-charged operation. The quasi-dimensional model couples a core gas zone to boundary layer and ring-pack crevice regions. The thermal boundary layer model is derived from energy considerations. The ring-pack model accounts for both ring position and flow exchange within its subvolumes.; Two engine platforms were utilized in this study for model validation and ultimate confirmation of HCCI operating strategies. Two-component fuel data, collected at Lund University on a Volvo TD100 engine, were used to evaluate the predictive capability of the C-4 chemical mechanism for different fuel-mixtures. In parallel, experimental data were acquired on a large-bore, Caterpillar 3500 single-cylinder engine that was operated in a turbo-charged configuration under a range of thermodynamic conditions, engine speeds and compression ratios.; The study has shown that a physically based quasi-dimensional model has the ability to accurately predict both HCCI engine performance as well as unburned hydrocarbon (UHC) emissions. Experiments confirmed that the engine could be operated in a stable configuration up to equivalence ratios of 0.32. The NOx emissions were on the order of .05g/kW-hr while the combustion efficiency ranged from 85–92%. Nevertheless, the engine thermal efficiency ranged from 30–39%, well below what was expected for HCCI operation.