(487t) Controlling CO and HC Emissions From High Efficiency Clean Combustion

Advanced diesel combustion regimes such as High Efficiency Clean Combustion (HECC) offer the benefits of reduced engine out NOX and particulate matter (PM) emissions. HECC combines high exhaust gas recirculation (EGR) rates to reduce the flame temperature (to lower NOX formation) and high fuel rail pressure with advanced injection timing to create near homogeneous air-fuel mixture prior to combustion (to reduce PM formation). Lower engine out emissions remove some burden from aftertreatment devices. Specifically, lower PM emissions during advanced combustion reduce the demand on diesel particulate filters (DPFs). Similarly, lower NOX emissions reduce the performance requirements of NOX control devices. While delivering low NOX and PM emissions, HECC produces much higher levels of carbon monoxide (CO) and hydrocarbons (HC) than conventional diesel combustion modes.

In this work, diesel oxidation catalysts with different platinum (Pt) loadings were investigated as means of controlling higher CO and HC emissions from HECC. The Pt loading varied from 40 to 100 g/ft3. Each DOC was evaluated on a 1.7-liter 4-cylinder diesel engine operating in high efficiency clean combustion under various operating conditions; for comparison, emission data was also collected from the engine operating at conventional combustion modes with and without EGR. Five steady-state operating conditions were evaluated. Each steady-state speed and load point represents typical operating conditions that vehicles may encounter during the Federal Test Procedure (FTP) driving cycle.

None of the DOCs evaluated were able to reduce CO at the low load settings during HECC mode, and 20 to 40% conversion was achieved during conventional combustion modes. The temperature of the exhaust entering the DOC was 130°C for HECC and 160°C for conventional modes. Complete reduction of CO was achieved at other load points when DOC operating temperature was above 230°C. Similar results were obtained for HC conversions. At the lowest load point, HC conversion varied from 30-60% for all of the combustion modes. At least 90% HC conversation was achieved at higher load points. It was found that light off temperatures (temperatures at which at least 90% conversion of CO and HC was achieved) when engine operated in HECC were 140°C and 148°C for DOCs with 100g/ft3 and 40g/ft3, respectively, which explains the inability of the DOCs to reduce HC and CO emissions at the lowest load point when temperatures were 130°C.