Volatile Organic Compounds in Exhaust Gas from Diesel Engines under Various Operating Conditions

Abstract

The volatile organic compounds (VOC) from diesel engines, including formaldehyde and benzene, are of concern and remain as unregulated harmful substances. These substances are positively correlated with total hydrocarbon (THC) emissions, but the VOC and aldehyde compounds at light load or idling conditions are more significant than THC. When coolant temperatures are low at light loads, there are notable increases in formaldehyde and acetaldehyde, and with lower coolant temperatures the increase in aldehydes is more significant than the increase in THC. With ultra-high exhaust-gas recirculation (EGR) suppressing in-cylinder soot and NO _x formation, VOC increase drastically with intake oxygen content below 14 per cent. These trends correlate well with the drastic increase in THC emissions. Oxidation catalysts are effective for reducing some VOC emissions, including aldehydes and some unsaturated hydrocarbons. However, aromatics and methane generated from ultra-high EGR, low-temperature smokeless combustion, are hardly reduced with the catalysts, particularly under overall rich conditions.