The Effect of Spark Timing on Engine–Out Hydrocarbon Speciation and Hydrocarbon Trap Performance

The performance of zeolite based, catalyzed hydrocarbon (HC) traps were evaluated with different inlet HC species and warm up profiles. Five different settings of cold–start spark timing were used each on separate FTP75 vehicle emission tests with constant neutral engine idle speed and fueling schedule. A test vehicle aftertreatment system that consisted of two converter assemblies, close-coupled and underbody, was modified by exchanging the bricks in the latter assembly with HC traps. With increasing spark retard from 9° BTDC to −17° BTDC, exhaust temperature increased, engine–out non–methane hydrocarbon (NMHC) emissions decreased, the concentration of large chain (C₆₊) HC species decreased and the small chain (C_2–3) HC species increased. Lab flow reactor experiments showed that HC traps do not effectively manage small chain HC species with efficient adsorption or retention to conversion. The vehicle test with the 9° BTDC spark timing showed the HC trap adsorbed NMHC emissions at an efficiency of 81% and converted it at 35%. The vehicle test with the –17° BTDC spark timing showed the HC trap adsorbed NMHC emissions at an efficiency of 68% and converted it at 36%. Engine operation at 9° BTDC spark timing minimized small chain HC species but caused the aftertreatment to warm up slowly and increased the HC emissions into the trap and out of the tailpipe. An optimal spark setting for HC trap adsorption efficiency and warm up was chosen and other cold start parameters were recalibrated, which yielded an NMHC adsorption efficiency of 75% and conversion efficiency of 51%.