Effects of Diesel Hydrocarbon Components on Cetane Number and Engine Combustion and Emission Characteristics

Abstract

Commercial diesel consists of hundreds of hydrocarbons such as alkanes, cycloalkanes, and aromatics. The components of the fuel’s composition are what determine its physical and ignition properties, and their variations affect engine performance. In this study, n-heptane, n-dodecane, tetralin, and decalin were chosen as typical additives to blend with commercial diesel according to the China VI standard (Heavy Duty Diesel Vehicle Pollutant Emission Limits and Measurement Methods) in 20% and 50% volume fractions, respectively. The physical properties of the fuel blends, such as viscosity, density, cetane number (CN), and distillation range, were measured first. Then, the commercial diesel’s lower heat value was measured, and blended fuels were calculated accordingly. The CN of the blended fuel is tested by an Ignition Quality Tester (IQT), which is known as the derived cetane number (DCN). The results show that adding n-dodecane increases the value of DCN, while tetralin reduces the DCN, and n-heptane and decalin have negative effects. This study uses a type of WP12 diesel engine made by Weichai that meets China’s emission regulation 6. During the tests, the fuel injection strategy was kept as a pure diesel operation without any modifications. Compared with pure diesel operation, the bench test results show the following characteristics: the maximum torque output increased with increased decalin, followed by tetralin and n-dodecane, while n-heptane has a side effect compared to pure diesel operation. The addition of n-dodecane and n-heptane can reduce fuel consumption, while tetralin will increase it, and decalin has no obvious effect on fuel consumption. It was found that n-heptane increases HC and NOx emissions significantly. Furthermore, n-dodecane slightly increases CO, HC and NOx emissions. Decalin increases CO and HC emissions when mixed in a large proportion. In addition, tetralin causes a substantial increase in HC, CO and NOx emissions at medium and high loads.