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Future LEV-III tailpipe (TP) emission regulations pose an enormous challenge forcing the fleet average of light-duty vehicles produced in the 2025 model year to perform at the super ultralow emission vehicle (SULEV-30) certification levels (versus less than 20% produced today). To achieve SULEV-30, regulated TP emissions of non-methane organic gas (NMOG) hydrocarbons (HCs) and oxygenates plus oxides of nitrogen (NOx) must be below a combined 30 mg/mi (18.6 mg/km) standard as measured on the federal emissions certification cycle (FTP-75). However, when flex-fuel vehicles use E85 fuel instead of gasoline, NMOG emissions at cold start are nearly doubled, before the catalytic converter is active. Passive HC traps (HCTs) are a potential solution to reduce TP NMOG emissions. The conventional HCT design was modified by changing the zeolite chemistry so as to improve HC retention coupled with more efficient combustion during the desorption phase.

In the development of HC traps (HCT) for reducing vehicle cold start hydrocarbon (HC)/nitrogen oxide (NOx) emissions, zeolite-based adsorbent materials were studied as key components for the capture and release of the main gasoline-type HC/NOx species in the vehicle exhaust gas. Typical zeolite materials capture and release certain HC and NOx species at low temperatures (<200°C), which is lower than the light-off temperature of a typical three-way catalyst (TWC) (≥250°C). Therefore, a zeolite alone is not effective in enhancing cold start HC/NOx emission control. We have found that a small amount of Pd (<0.5 wt%) dispersed in the zeolite (i.e., BEA) can significantly increase the conversion efficiency of certain HC/NOx species by increasing their release temperature. Pd was also found to modify the adsorption process from pure physisorption to chemisorption and may have played a role in the transformation of the adsorbed HCs to higher molecular weight species.

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 (C2–3) 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 majority of unburned hydrocarbon emissions from vehicles occur during cold start operation of the vehicle before the catalyst system has heated to the point where it has reached high operating efficiency. One promising technology to reduce cold start hydrocarbon emissions is the catalyzed hydrocarbon trap. This paper presents the results of a vehicle, laboratory, and modeling study of the performance of this relatively new type of catalyst. A procedure to evaluate trap performance in the laboratory is presented that correlates well with trap performance on a vehicle. Additionally, a mathematical model of the catalyzed hydrocarbon trap is presented. This model utilizes laboratory determined parameters to calibrate the model for specific catalyzed hydrocarbon trap formulations to simulate the performance of that formulation on a vehicle. Data is presented that shows the model agrees well with vehicle data during the bag 1 portion of the Federal Test Procedure.