The present paper describes the results of a cooperative research project between GM Powertrain Europe and Istituto Motori - CNR aimed at studying the impact of both fresh and highly oxidized RME at two levels of blending on spray formation and combustion in modern automotive diesel engines. The tests were performed on an optical single-cylinder engine sharing combustion system configuration with the 2.0L Euro5 GM diesel engine for passenger car application.
Two blends (B50 and B100) blending were tested for both fresh and aged RME and compared with commercial diesel fuel in two different operating points typical of NEDC (1500rpm/2bar BMEP and 2000rpm/5bar BMEP). The experimental activity was devoted to an in-depth investigation of the spray density, breakup and penetration, mixture formation, combustion and soot formation, by means of optical techniques.
The optical engine results have confirmed that, from a combustion point of view, there is no appreciable difference between fresh and aged RME. Furthermore, the tests highlighted the higher spray penetration of RME with respect to regular diesel fuel as well as a differences in density distribution across the spray, breakup angle and soot formation The soot evolution was lowered due to lack of aromatics precursors and the high oxygen concentration in the fuel.