Ojapah, M., Zhao, H., and Zhang, Y., "Effects of Ethanol on Part-Load Performance and Emissions Analysis of SI Combustion with EIVC and Throttled Operation and CAI Combustion," SAE Technical Paper 2014-01-1611, 2014, doi:10.4271/2014-01-1611.
Internal combustion engines are subjected to part-load operation more than in full load during a typical vehicle driving cycle. The problem with the Spark Ignition (SI) engine is its inherent low part-load efficiency. This problem arises due to the pumping loses that occur when the throttle closes or partially opens. One way of decreasing the pumping losses is to operate the engine lean or by adding residual gases. It is not possible to operate the engine unthrottled at very low loads due to misfire. However, the load can also be controlled by changing the intake valve closing timing - either early or late intake valve closing. Both strategies reduce the pumping loses and hence increase the efficiency. However the early intake valve closure (EIVC) can be used as mode transition from SI to CAI combustion. In recent years, in order to develop more efficient and cleaner gasoline engines, a number of new engine operating strategy have been proposed and many have been studied on different engines but there is a lack of direct comparison between various operating strategies and alternative fuels at different SI and CAI modes. In this paper, the performance, combustion and emission were measured and compared between throttled SI, EIVC and CAI combustion with negative valve overlap (NVO) of gasoline and its mixture with ethanol (E15 and E85) were measured and analysed. At part-load condition, it is found that the CAI combustion produced the lowest fuel consumption and NOx emissions. The EIVC operation led to a moderate improvement in the fuel conversion efficiency over the throttled SI operation but it was characterised with the slowest combustion and worst HC and CO emissions. Less and smaller particles numbers were detected for EIVC E0 and E15 fuel blends. The particulate emission results showed that soot is the dominant particles in the exhaust, which could be reduced by leaner mixture combustion.