Hydrogen Assisted Jet Ignition (HAJI) is a novel method of maintaining combustion stability during ultra-lean operation of conventional, homogeneously charged, SI engines. When operating with HAJI above λ=2, CO and NOx emissions fall to low levels while HC emissions rise to approximately double their stoichiometric value.
HC emissions were investigated by operating a HAJI equipped, optically accessible, four-valve single cylinder engine at 600 r/min, wide open throttle (WOT), and from λ=1 to λ=2.4. A fast flame ionisation detector was used to collect real time hydrocarbon concentration data from behind one of the exhaust valves, inside the HAJI pre-chamber, and from near the combustion chamber wall. Flame images were also obtained.
Exhaust port sampling shows that the HC concentration during blowdown and early exhaust is increased, but the concentration at the end of exhaust is decreased. Sampling from within the HAJI prechamber indicates that the prechamber is not acting as a HC storage mechanism, or ‘large crevice’. In-cylinder sampling near the wall shows that a thicker wall quench layer forms and is maintained throughout the cycle. This wall layer is markedly reduced in the region where the HAJI jet impinges on the wall. The structure and shape of the HAJI flame images support these findings.