Analysis of Different Internal EGR Solutions for Small Diesel Engines

Although the use of Exhaust Gas Recirculation (EGR) is nowadays mandatory for automotive diesel engines to achieve NOx emissions levels complying with more and more stringent legislation requirements, electronically controlled EGR systems still represent an expensive technology, often unsuitable for small diesel engines for off-road applications or for two/three wheelers. An interesting option for these categories of small diesel engines is the so-called “internal EGR”, which is obtained by modifying the intake or the exhaust valve lift profile, in order to increase the fraction of exhaust residuals at the end of the intake stroke. Different valve lift profiles were therefore evaluated for a 2 cylinders, 700 cc, Lombardini IDI diesel engine, equipping a light 4 wheelers vehicle. Firstly, the load and speed operating points of the engine over the ECE-40 driving cycle were evaluated and a set of 5 operating points, representative of more than 60% of total engine emissions were identified. Afterwards, by means of a 1D fluid dynamic model of the engine, the fraction of internal residuals that could be obtained with different valve lift profiles was evaluated, and the more promising lift profiles were selected for the following experimental tests. Finally, the lift profiles selected through the previous analysis were experimentally tested on the 5 operating points representative of the ECE-40 driving cycle, highlighting a potential for appreciable (up to 13%) reduction of NOx emissions without remarkable detrimental effects on fuel consumption.