The Secondary Organic Carbon (SOC) Formation from a CRDI Automotive Diesel Engine Exhaust 2011-01-0642

Condensed soot coming out of vehicular exhaust is commonly classified as organic carbon (OC) and elemental carbon (EC). OC can be directly emitted to the atmosphere in the particulate form (primary carbon) from the tailpipe or can be produced by gas-to-particle conversion process (secondary organic carbon, SOC). Under typical atmospheric dilution conditions, most of the semi-volatile material is present in the form of soot. SOC holds wider implications in terms of their adverse health and climate impact. Diesel exhaust is environmentally reactive and it has long been understood that the ambient interaction of exhaust hydrocarbons and NO_x results in the formation of ozone and other potentially toxic secondary organic carbon species.

The current emission norms look at the primary emissions from the engine exhaust. Also, research efforts are geared towards controlling the emissions of primary carbon. However the secondary organic carbon produced as a result of gas-to-particle conversion upon mixing of gaseous tailpipe emissions with the ambient air in presence of sunlight is also of significant importance. Therefore evaluation of gaseous emissions from engine exhausts using an artificial photochemical chamber mimicking the atmospheric conditions can serve as an important tool to assess the potential adverse health impact of secondary engine emissions. A modern common rail direct injection engine has been chosen as the emission source for the current investigation using mineral diesel. The main objective of this study was to look at the ratio or percentage change between the primary and secondary tailpipe emissions with focus on SOC using diesel fuel at different engine load conditions using an optimized photochemical chamber. Through these experiments, an attempt has been made to investigate the SOC yield from diesel-fuelled CRDI engine under fairly moderate ageing conditions for different load conditions at rated engine speed. The ageing of exhaust emission was done for RH varying from 40-60% and temperature range of 35-40°C. Primary emissions of OC, EC and PAHs increased in diesel exhaust with increasing engine load. With increase in engine load, rate of primary EC emissions is higher than rate of increase of OC emissions. Particle bound PAHs increases by an order of magnitude after ageing, which indicates that the toxic potential of diesel engine exhaust might increase an order of magnitude even under moderate ageing conditions.