The influence of fuel injection timing on precombustion mixing of diesel fuel and air, combustion, and emissions at early-injection conditions similar to homogeneous charge compression−ignition (HCCI) engine conditions was investigated experimentally in an automotive-size compression−ignition engine and a constant-volume vessel. The injection timing was controlled by electronic fuel injection equipment. In-cylinder pressure measurements, engine-out emission measurements, and imaging of the spray development were used to analyze the ignition delay period and fuel distribution. The ignition delay period was measured over a wide range of injection timings as well as at various compression ratios and engine speeds. With advancing fuel injection timing, the ignition delay increased and the engine-out nitrogen oxides (NO x ) decreased, suggesting that increased premixing time results in a lean mixture and low flame temperature. It was also found that the ignition delay period to decrease NO x emissions to a negligible level was almost the same under any compression ratio or engine speed. From the emissions measurements, a drastic decrease in smoke, hydrocarbon (HC), and carbon monoxide (CO) emissions was observed at specific early-injection timing. To clarify the source of the observed behavior, the diesel spray impinging on the surface of a combustion chamber was visualized in a constant-volume vessel simulating in-cylinder environments under early-injection conditions. The images show that diesel spray should target the bowl-lip area to enhance precombustion mixing, which would be desirable for reducing incomplete combustion products.

No abstract

No abstract

The effects of operating factors on a gasification system were reviewed by comparing a computational simulation and real operation results. Notable operation conditions include a conveying gas/coal ratio of 0.44, an oxygen/ coal ratio of 0.715, a reaction temperature of 1,000 o C, and reaction pressure of 5bar in the case of Adaro coal; based on this, the cold gas efficiency was estimated as 82.19%. At the point of the reaction temperature effect, because the cold gas efficiencies are more than 80% when the reaction temperatures are higher than 900 o C, the gasifier inner temperature must remain over 900 o C. At high reaction temperature such as 1,400 o C, the reaction pressure shows little effect on the cold gas efficiency. The addition of steam into the gasifier causes an endothermic reaction, and then lowers the gasifier outlet temperature. This is regarded as a positive effect that can reduce the capacity of the syngas cooler located immediately after the gasifier. The most significant factor influencing the cold gas efficiency and the gasifier outlet temperature is the O 2 /coal ratio. As the O 2 /coal ratio is lower, the cold gas efficiency is improved, as long as the gasifier inner temperature remains over 1,000 o C. With respect to the calorific value (based on the lower heating value, LHV) of produced gas per unit volume, as the N 2 /coal ratio is increased, the calorific value per syngas unit volume is lowered. Decreasing the amount of nitrogen for transporting coal is thus a useful route to obtain higher calorific syngas. This phenomenon was also confirmed by the operation results.

No abstract