Combustion and Emissions of a Common-Rail Diesel Engine Fueled with HWCO

Hydrotreated vegetable or waste cooking oils (HVOs or HWCOs) are considered second-generation biofuels and are regarded as a promising alternative to current market diesel because they mainly consist of paraffinic hydrocarbons. This paper presents an experimental investigation conducted in order to examine the potential of HWCO as a substitute of diesel fuel. The HWCO used was produced from waste cooking oils through a catalytic hydrotreatment process. The main target of the study was the investigation of the emissions and combustion characteristics of the HWCO in comparison with conventional diesel. To that aim, a light-duty common-rail Euro 5 diesel engine, running on neat HWCO, was tested over the New European Driving Cycle (NEDC) at the engine test bed. The results showed lower CO2, CO, and hydrocarbon emissions, but increased NOx emissions. Combustion analysis, performed at specific steady-state operating points, revealed the differences in the combustion mechanism between HWCO and market diesel, forming a basis for the interpretation of emissions results.