Effects Of Doc And/or Poc On The Exhaust Emissions From Diesel Engine

As an important aftertreatment way to meet Euro IV standard emissions regulation, diesel oxidation catalyst (DOC) and particulate oxidation catalyst (POC) have presently been applied on several diesel engines in the world. To provide fundamental database for the further acceptance, tests for five different DOC and/or POC aftertreatments were conducted on a common–rail heavy-duty diesel engine, coupled with AVL partial flow dilution channel system and Horibar exhaust gas analyzer. Meanwhile, the polycyclic aromatic hydrocarbons (PAHs) in soluble organic fraction (SOF) were measured by gas chromatography-mass spectrometry (GC-MS). The effects of DOC and/or POC on the regulated emissions and unregulated emissions were investigated and the main research conclusions of this dissertation are as follows:1. At the European steady state cycle (ESC), the presence of DOC+POC on the diesel engine led to a maximum decrease of 98% in the brake specific emission of carbon monoxide (CO), 97.1% in the brake specific emission of hydrocarbon (HC) and 60.4% in the brake specific emission of particulate matter (PM), respectively. However, a slightly change was observed for the brake specific emission of nitrogen oxides (NOx), with a less than 10% reduction. At the European transient cycle (ETC), the application of DOC+POC on the diesel engine resulted in a maximum decrease of 97.1% in the brake specific emission of CO, 94.2% in the brake specific emission of HC and 65% in the brake specific emission of PM, respectively. However, a slightly change was also observed for the brake specific emission of NOx, with a less than 10% reduction.The engine dynometer test result showed that the diesel engine with DOC+POC could meet the Chinese phaseⅣemissions regulation.2. Under steady operating conditions, the brake specific emissions of formaldehyde, acetaldehyde and nitric oxide (NO) showed obvious decreases when the DOC+POC were used. The higher the catalytic activity of DOC and the lower air speed were, the more noticeable reductions for formaldehyde, acetaldehyde and NO were obtained. The maximum decreases were 82% for formaldehyde, 98% for acetaldehyde and 62% for NO, respectively. The brake specific emission of sulfur dioxide (SO2) also gave a decrease when the DOC+POC were used. The lower brake specific emission of SO2 and resistance of DOC+POC to sulfide were attained in the case of the higher catalytic activity of DOC and the lower air speed.3. With DOC+POC on the diesel engine, the brake specific emissions of PAHs and SOF presented pronounced decreases.Under the ESC and ETC conditions, the maximum decreases of SOF were 75% and 40%, respectively. The higher catalytic activity of DOC and POC and the lower air speed resulted in a more effective oxidation of PAHs. The maximum decreases of PAHs were 28% for the ESC and 55% for ETC, respectively.4. The brake specific emissions of 2, 3 and 4 aromatic rings in PAHs showed noticeable decreases with DOC+POC on the diesel engine, where the decrease for 4-ring PAHs was the most significant. The higher the catalytic activity of DOC and POC and the lower the air speed, the more effective the oxidation of 4-ring PAHs. Under the ESC and ETC conditions, the maximum reductions of 4-ring PAHs were 61% and 81%, respectively.