Internal Exhaust Gas Recirculation for Efficiency and Emissions in a 4-Cylinder Diesel Engine 2016-01-2184
The application of stringent requirements on emission reduction and higher fuel economy in diesel engines has led to the need for efficient energy extraction in the cylinders and reductions in exhaust gas temperatures, as well as posing challenges for energy availability for emission control systems. Internal exhaust gas recirculation (I-EGR) can increase the exhaust gas temperature and reduce engine-out gaseous emissions. The secondary opening of exhaust valves in a diesel engine produces an efficient recirculation of exhaust gases from the previous engine cycle to the cylinder mass charge during the intake stroke. However, I-EGR alone can increase exhaust gas temperature only up to a limit determined by the resulting increase in soot emissions. To obtain higher exhaust gas temperatures, I-EGR can be combined with multiple injections after the main injection event, thereby altering the heat release rate and the exothermic reactions in the exhaust stroke. Based on experimental observations, it is feasible to maintain or reduce engine-out emissions of nitrogen oxides while achieving simultaneous reductions in hydrocarbons and carbon monoxide. In this paper, one-dimensional computational methods combined with experimental bench tests are applied to analyze the performance of a four-cylinder diesel engine using I-EGR. The impact of I-EGR on transient test cycles is determined for different valve event configurations. One, two, or continuously selectable exhaust valve profiles are applied for phasing and lift variation in the recirculation flow area.