A 1-D GT-Power model based investigation has been carried out to identify the impact of late intake valve closing (LIVC) on fuel economy and emission reduction of a modern small bore diesel engine. The diesel engine examined employed a variable turbine geometry (VTG) turbocharger with air-to-air charge cooler, cooled low pressure exhaust gas re-circulation (LP-EGR), and cooled high pressure exhaust gas re-circulation (HP-EGR). The LIVC system investigated varied the closing time of the intake valve by increasing or decreasing the dwell at the maximum valve lift point.
This paper describes how the fuel economy and NOx emission of the diesel engine were affected by varying the intake valve closing time. The intake valve closing time was delayed by as much as 60 degrees. The intermediate speed, low load 3000 rpm, 5 bar BMEP, 10% HP - EGR, and 2000 rpm, 4 bar BMEP, 10% LP - EGR operation points were chosen as the engine running conditions, since turbocharger potential at these conditions can be greatly explored to investigate the variable valve timing effect. By combining variable valve timing technology with VTG turbocharger, engine out NOx emission can be greatly reduced by 24% without sacrificing fuel economy. For some LIVC, BSFC can even be decreased by 1%.
The reason for the better fuel economy was investigated. It was found that LIVC coupled with the VTG turbocharger moved the operating point to a more efficient region, reducing the fuel consumption. At the same time, the NOx reduction caused by the lower in-cylinder temperature from late intake valve closing was also analyzed in detail. In another investigation, O2 level was found to be important in understanding the NOx reduction benefit.