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Multi-dimensional computations were made of spark-ignited premixed-charge combustion in two engines having pent-roof-shaped combustion chambers and two intake valves per cylinder, one with a central spark plug and the other with dual lateral spark plugs. The basic specifications for the two engines were the same except for differences in the number of spark plugs and exhaust valves. The effects of swirl and equivalence ratio on combustion, wall heat transfer, and nitric oxide emission characteristics were examined using a global combustion model that accounts for laminar-kinetics and turbulent-mixing effects. The initial conditions on both mean-flow and turbulence parameters at intake valve closing (IVC) were estimated in order to simulate engine operation either with both intake valves active or with one valve deactivated. The predictions were compared with experimentally derived pressure-time, heat loss, and nitric oxide emission data.

Homogeneous Charge Compression Ignition (HCCI) combustion is known for its significant fuel economy benefit with near-zero NOx and particulate emissions. Stable HCCI combustion relies on a well-controlled temperature and composition of the cylinder charge at the intake valve closing that in turn requires a precise coordination of all engine inputs. In this paper, the HCCI combustion is realized by retaining hot residual from the previous combustion event using the recompression valve strategy. The recompression valve strategy closes the exhaust valves before the top dead center and opens the intake valves at an angle symmetric to the exhaust valve closing. Depending on the engine load, different valve open/close timings with respect to the crank position are used to trap different amounts of residual gases. It is critical to coordinate the change in the valve open/close timings with the change in the injected fuel quantity during load transients in order to maintain stable combustion.