A computational system optimization was conducted to explore the potential benefits of diesel reforming in dual-fuel combustion strategies. A comprehensive CFD model, validated against syngas (50/50 /CO by mole) metal engine experiments, was used to simulate the engine combustion process. The engine CFD solver was coupled with an equilibrium solver for the reformer process and three different reforming processes were investigated: Partial oxidation, steam reforming, and autothermal reforming. A system level approach was used to evaluate the impact of thermochemical recovery of exhaust energy and reformer losses. A design of experiments of simulations was conducted to explore the combustion system design space and a genetic algorithm was used to search the resulting response surface and find the optimal operating conditions. It was found that fuel reforming can increase engine net indicated efficiencies by as much as 9% due to a shorter combustion duration and reduction in heat transfer losses. The partial oxidation reforming system resulted in the lowest system efficiencies at 44% due to its exothermic nature, while steam reforming and autothermal reforming were able to achieve over 48% system efficiency, an improvement in global efficiency of 8% compared to a diesel baseline due to exhaust heat recovery.

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Due to growing interest in utilizing natural gas as an alternative fuel in internal combustion engines, a study on the use of natural gas for dual-fuel combustion strategies in a heavy-duty engine was performed to examine the diesel pilot ignition (DPI) and reactivity controlled compression ignition (RCCI) combustion strategies. In Part 1 of this work, the transition between the DPI and RCCI combustion regimes was studied via the direct control of the SOI timing. At the relatively rich condition of ϕ = 0.72, the performance of both combustion strategies was comparable. In Part 2 of this work, the effect of the equivalence ratio on each combustion regime was examined. It was observed that at richer conditions the performance of each combustion regime was similar. However as the conditions became leaner, the performance improved for RCCI combustion and was degraded for DPI combustion. In Part 3 of this work, the effect of fueling rate was explored at a relatively lean operating condition (ϕ = 0.52). It was seen that the fueling rate has little effect on the combustion performance as the engine load was increased. The strong influence of the equivalence ratio on the combustion performance of the RCCI and DPI combustion strategies indicates the both combustion regimes are recommended to engine applications with air handling systems which generate relatively rich in-cylinder conditions; for engine applications with air handling systems which allow for relatively lean in-cylinder conditions, the RCCI combustion regime is recommended.

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