Effect of 2-Ethylhexyl Nitrate Cetane Improver on NOxEmissions from Premixed Low-Temperature Diesel Combustion

Production implementation of premixed low-temperature diesel combustion (LTC) is highly attractive because it can lead to low engine-out particulate matter (PM) and NOx emissions. It is important for LTC strategies to yield acceptable emissions while consuming commercially available fuel, whose properties vary substantially and which contains various additives. The chemical reactions of 2-ethylhexyl nitrate (2-EHN), an additive used to increase the cetane number of a diesel fuel, show potential to increase the NOx emissions of a diesel engine. While 2-EHN has been widely shown to not affect the emissions of conventional diesel combustion, few results are available for LTC, which features different combustion characteristics and significantly lower NOx emissions. This paper demonstrates the effect of using a fuel doped with 2-EHN cetane improver in a direct-injection, diesel-fueled LTC operating mode. Testing was conducted at a light-load condition on a modern single-cylinder engine, fueled with two sets of test fuels at matching cetane numbers (47 and 53), with some test fuels using 2-EHN cetane improver. The addition of 2-EHN to the fuel increases the engine-out NOx for the tested LTC operating condition. Decomposition of the nitrate cetane improver forms NO and NO2 in significant quantities relative to the low engine-out NOx emissions from LTC.