Statistical Quantification of Knock With Spark Ignition and Pre-Chamber Jet Ignition in a Light Duty Gasoline Engine

Knock is a major challenge for high load operation of spark ignited gasoline engines with higher compression ratios, since the end-gas undergoes higher temperature and pressure trajectories during combustion. Pre-chamber combustion creates long-reach ignition jets that have the potential to mitigate knock due to their rapid consumption of end-gas. However, conventional pressure oscillation-based knock metrics may not accurately capture the end-gas autoignition severity in pre-chamber systems due to differences in ignition and combustion behavior. This work investigates the knock behavior of both traditional spark ignition and pre-chamber combustion (including different nozzle designs) in a high compression ratio engine fueled with regular octane certification gasoline. The data was analyzed using statistical methods to show the random nature of knock events. Detailed analysis was used to explain the pressure oscillations of both knocking and non-knocking cycles of pre-chamber jet combustion and show that conventional pressure oscillation-based knock metrics may not adequately quantify end-gas autoignition severity. A novel knock metric is introduced to avoid consideration of the non-knock related pressure oscillation and better quantify the end-gas autoignition severity. The new metric was used to explain the knock mitigation mechanism for pre-chamber jet combustion and demonstrate an additional pre-chamber jet ignition benefit of reduced combustion variability during engine operation with cooled exhaust gas circulation within its dilution limit.

Furnace Design for Improved Exhaust Gas Circulation and Heat Transfer Efficiency

In the aluminum production industry, metal furnaces are operated by diffusion flame over the metal surface to maintain the aluminum metal at the set point temperature for alloying and casting. Heat is transferred from the flame and its exhaust gases to the metal surface via radiation and convection. The exhaust gases leaves through the furnace’s chimney carrying a significant amount of waste heat to the atmosphere. Furnace efficiency could be improved by enhancing the heat transfer inside the furnace. In this study, a validated full-scale 3-D CFD model of a natural gas fired aluminum furnace is developed to investigate the effect of flue gas ventilation configurations and burner operating conditions on the heat transfer inside the furnace. Onsite measurements are carried out for the fuel and airflow rates as well as flue gas temperature. Four flue ventilation configurations are considered with eight furnace’s operation modes. The flue-gas’s waste-heat varies from 49–58%, with the highest value occurring at the high-fire operating mode. This indicates a significant room for improvement in the furnace performance. Results suggest that a symmetrical positioning of the exhaust duct favors effective exhaust gas circulation within the furnace and hence, increases hot-gases’ heat-transfer effectiveness inside the furnace. These results provide some guidelines for optimal aluminum reverberatory furnace designs and operation.

Gas circulation rate and medium exchange ratio as influential factors affecting ethanol production in carbon monoxide fermentation using a packed-bed reactor

A packed-bed reactor (PBR) which has recyclable internal gas and medium exchange functions for carbon monoxide (CO) fermentation was operated using an ethanol producing acetogen, Clostridium autoethanogenum DSM 10061.