Regulated emissions and speciated hydrocarbons from smokeless low-temperature combustion diesel engines with ultra-high exhaust gas recirculation and exhaust oxidation catalyst

Abstract

Abstract

With ultra-high exhaust gas recirculation (EGR) suppressing the in-cylinder soot and nitrogen oxides (NO _x ) formation as well as with the exhaust oxidation catalyst removing the engine-out total unburned hydrocarbon (THC) and carbon monoxide (CO) emissions, clean diesel combustion in terms of low regulated emissions (NO _x , particulate matter, THC, and CO) can be established in an operating range up to 50 per cent load. However, unregulated emissions such as aldehydes, aromatics, and 1,3-butadiene, which are seen as a severe threat to human health, are concerned when operating the engine with ultra-high EGR. In this study, the THC emissions from a diesel engine operated with ultra-high EGR low-temperature combustion were speciated using Fourier transform infrared spectroscopy. Some unregulated toxic emissions including aldehydes, aromatics, 1,3-butadiene, and some low molecular hydrocarbons dramatically increase in the ultra-high EGR low-temperature combustion regime. The exhaust oxidation catalyst is effective to remove aldehydes and some unsaturated hydrocarbons, but aromatics and methane generated from the ultra-high EGR operation are hardly reduced, particularly at higher loads.