Extension of the Lean Limit of Gasoline Engines Under Part Load by Using Hot Surface Assisted Spark Ignition (HSASI)

Charge dilution by lean-burn is one way to increase the efficiency of spark ignition engines while reducing NO_x emissions. This work focuses on increasing the flammability of lean mixtures inside a passive pre-chamber spark plug by elevating its temperature with the help of a controllable hot surface integrated into the pre-chamber. Thus, an extension of the lean limit under part load is aimed for. A pre-chamber spark plug prototype with an integrated, controllable glow plug was developed, called Hot Surface Assisted Spark Ignition (HSASI). Experimental investigations were conducted on a single-cylinder engine at the Karlsruhe University of Applied Sciences. Operating modes with an active glow plug (HSASI) and a non-active glow plug were compared. The lean limit for both operation modes were determined under part load. NO_x, CO and THC emissions were measured for different air-fuel equivalence ratios λ. The lean limit is extended by more than 0.1 in λ at low loads with HSASI operation. At constant λ, lower CO and THC emissions are achieved under HSASI operation than in operation with a non-active glow plug. NO_x-emissions are higher with an active glow plug at lower λ and align with higher λ. HSASI operation shows higher combustion stability, as combustion in the pre-chamber is accelerated and flame quenching in the pre-chamber is reduced.