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Lean burn natural gas engines have high potential in terms of efficiency and NOx emissions in comparison with stoichiometric natural gas engines, and much lower particulate emissions than diesel engines. They are a promising solution to meet the increasingly stringent exhaust emission targets for both light and heavy-duty engines. Partially Stratified-Charge (PSC) is a novel concept which was conceived by prof. Evans (University of British Columbia, Vancouver). This technique allows to further limit pollutant emissions and improve efficiency of an otherwise standard spark-ignition engine fuelled by natural gas, operating with lean air-fuel ratio. The potential of the PSC technique lies in the control of load without throttling by further extending the lean flammability limit.

Conversion from diesel to dual fuel (diesel and natural gas) operation may represent an attractive retrofit technique to get a better PM-NOx trade-off in a diesel engine, with no major modifications of the original design. In the proposed paper, an Euro 2 heavy duty diesel engine, converted for dual fuelling, has been studied and tested to reduce pollutant emissions. Throttled stoichiometric with EGR and lean burn technologies have been selected as control strategies. A mixed experimental-numerical approach has been utilized to analyze the engine behavior by varying key operating conditions such as throttling, natural gas/diesel oil percentage and EGR. The model, based on a 3D approach, has been used mainly to understand the evolution of the distribution of the most important parameters in the combustion chamber.

A Large Eddy Simulation (LES) numerical study of the Partially Stratified Charge (PSC) combustion process is here proposed, carried out with the open Source code OpenFOAM, in a Constant Volume Combustion Chamber (CVCC). The solver has already been validated in previous papers versus experimental data under a limited range of operating conditions. The operating conditions domain for the model validation is extended in this paper, mostly by varying equivalence ratio, to better highlight the influence of turbulence on flame front propagation. Effects of grid sizing are also shown, to better emphasize the trade-off between the level of accuracy of turbulent vortex description, and their impact on the kinematics of flame propagation. Results show the validity of the approach that is evident by comparing numerical and experimental data.

The aim of this work is to carry out statistical analyses on simulated results obtained from large eddy simulations (LES) to characterize spark-ignited combustion process in a partially premixed natural gas mixture in a constant volume combustion chamber (CVCC). Inhomogeneity in fuel concentration was introduced through a fuel jet comprising up to 0.6 per cent of the total fuel mass, in the vicinity of the spark ignition gap. The numerical data were validated against experimental measurements, in particular, in terms of jet penetration and spread, flame front propagation and overall pressure trace. Perturbations in key flow parameters, namely inlet velocity, initial velocity field, and turbulent kinetic energy, were also introduced to evaluate their influence on the combustion event. A total of 12 simulations were conducted.

The aim of this work is to assess the accuracy of results obtained from Large Eddy Simulations (LES) of a partially-premixed natural gas spark-ignition combustion process in a Constant Volume Combustion Chamber (CVCC). To this aim, the results are compared with the experimental data gathered at the University of British Columbia. The computed results show good agreement with both flame front visualization and pressure rise curves, allowing for drawing important statements about the peculiarities of the Partially Stratified Combustion ignition concept and its benefits in ultra-lean combustion processes.